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Biological Control and Pest Control Science

Integrated Pest Management (IPM)

Biological Control Research Organization

Pest-Upset Versus Pest Resurgence

Expansion of Biological Control into New Study Areas

Drawbacks of Chemical Control

Important Factors Affecting Research in Biological Control

Selective Pesticides

The Political Economy of Biocontrol Research & Research Needs

Factors Determining Physical Selectivity

Socio-Economics of Biological Control

Van Driesche & Bellows (1998) Account


Conditions Favoring the Adoption of Bicontrol Strategies

Classical Biological Control

Political and Economic Framework For Biological Control

Augmentative Biological Control

The Importance of Defining Biological Control

Conservation     Habitat Alteration

Difficulties Encountered in the Measurement of Biocontrol


Resource Allocation For Research


Size of Research Effort

[Please refer also to Selected Reviews 

            &  Detailed Research ]



I. The phenomenal development and increased use of organic pesticides in agriculture after 1945 has been a mixed blessing and has led to heated contemporary debates.

A. An attitude of unreserved optimism became prevalent among most entomologists with demonstrations of the spectacular effectiveness of DDT.

B. Failures of synthetic organic insecticides to control all pests have changed this attitude to a more rational but somewhat pessimistic one.

C. Development of insecticide resistant populations, resurgence of treated pest populations, evaluation of secondary pests (or in some cases previously innocuous species) to a status of primary importance, deleterious effects on populations of nontarget organisms, and general pollution of the environment with measurable residues of persistent chemicals have posed increasingly critical problems.

II. It is not surprising, then, that considerable interest has been shown in recent years in Integrated Pest Management (IPM). or the ecological approach.

III. The term "Integrated Control" apparently was first proposed by Dr. Blair Bartlett, University of California, Riverside in 1956, although the first actual demonstration of the technique was by the Swiss entomologist, F. Schneider in Sumatra in the 1940's and working on gambir plantations.

A. Bartlett used the term to designate applied pest control that combines and integrates biological and chemical measures into a single unified pest control program.

B. Chemical control is used only where and when necessary, and in a manner that is least disruptive to beneficial regulating factors of the environment, particularly naturally occurring arthropod parasitoids, predators and pathogens.

    IV. In the early 1960's the first suggestions arose for broadening the concept to include the integration, not only of chemical and biological control method, but of all practices, procedures and techniques relating to crop production, into a single unified program aimed at holding pests at subeconomic levels. Thus, the concept evolved from a two-component system (chemical and biological control) to the much broader concept of pest management.

V. All the proposed definitions have one common theme: the system must be based on sound ecological principles.

VI. Terms frequently used in discussions of integrated pest management:

A. Each species of arthropod pest occurring in our various agricultural ecosystems falls into one of three categories: key pest, occasional pest, or potential pest.

B. Usually one or two key pest species are common to each agricultural ecosystem, these being those serious, perennially troublesome species that dominate control practices.

C. Occasional pests, in contrast to key pests, are those arthropods that only cause economic damage in certain places in certain years. Such pest are usually under adequate biological or natural control which is disrupted occasionally or fails for various reasons.

D. Potential pests are those species which normally cause no economic damage, but as a result of chemicals or cultural practices are allowed to realize their potential for damage.

1. Basic to the concept of integrated pest management is the notion that most potential pests have effective natural enemies. All but the most sterile human-made environments have some biotic agents that influence pest populations; and due consideration should be given to the conservation or augmentation of these agents during the development of pest control programs insufficient ( Legner 1970, 1987 , Legner & Olton  1968,  1970 ,  Legner & Sjogren  1984, 1985; Legner et al. 1974, 1975, 1981 ; Oatman 1962).

2. Also basic is the concept that the ability of natural enemies to effect only partial control of a pest should not invoke chemical control practices that disrupt either this partial control or the controlling action of natural enemies of other potential pests in the agricultural ecosystem.

VII. Pest-Upset versus Pest Resurgence.

A. Pest-Upset.

1. cotton leaf perforator, a lepidopterous cotton defoliator, apparently native to the Southwestern United States, was inconspicuous until about 1965.

2. it became a cotton pest coincident with the massive blanket application of insecticide in the lower Sonora Desert cotton-growing areas, for the eradication of the newly introduced pink bollworm.

B. Pest Resurgence.

1. represents a rapid return to economic prominence of a pest whose abundance was initially suppressed by a pesticide that, however, destroyed its natural enemies.

2. this type of outbreak commonly results whenever pesticides destroy the partially effective natural enemies of a pest species.

3. pest resurgences often generate a need for increasingly frequent pesticide applications as the effects of additional natural enemy destruction accumulate with each treatment.

VIII. Sole reliance on chemicals for pest control has the following drawbacks:

A. Selection of resistance to insecticides in pest populations. Cross resistance also is hastened.

B. Resurgence of treated populations.

C. Outbreaks of secondary pests.

D. Residues, hazards and legal complications.

E. Destruction of beneficial species, including parasitoids, predators and pollinating insects.

F. Expense of pesticides, involving recurring costs for equipment, labor and material.

IX. Selective Pesticides.

A. "Selectivity" defines the capacity of a pesticide to spare natural enemies while destroying their pest host.

B. Two types of selectivity:

1. physical: arises from differential exposure of pests and natural enemies to a pesticide.

2. physiological: arises from a differential inherent susceptibility on the part of the pest and its natural enemies to a pesticide.

X. Factors that can determine physical selectivity.

A. Preservation of natural enemy reservoirs during treatment, either within treated areas or within easy migrational distances from them.

1. maintain adjoining untreated crop areas or stands of untreated alternate host plants.

2. recolonizing treated areas with mass-reared natural enemies.

3. staggering chemical treatments of portions of large plantings.

4. employing spot or strip treatments of chemicals.

B. Timing pesticide treatments to allow for the differential susceptibility and seasonal occurrence of the various developmental stages of natural enemies.

1. the pupal and prepupal stages of parasitoids are relatively immune to pesticides.

2. the eggs of many predators are laid in protected spots or are otherwise inherently unsusceptible.

3. adult parasitoids and predators are generally the most susceptible stages.

C. Physical selectivity may also be conferred by the feeding habits of various natural enemies.

1. internal parasitoid larvae are protected within their hosts from contact poisons.

2. adult entomophagous insects vary in susceptibility to stomach poisons in relation to their propensity to ingest insecticide contaminated hosts, plant exudates or honeydew.

D. Physical selectivity also can be conferred by manipulating the dosage and persistence of pesticides.

XI. Physiological selectivity is conferred by a pesticide that is more toxic to a pest species than to its natural enemies. But, unfortunately, the reverse is usually true.

A. A few pesticides have been developed that are fairly specific against certain groups or species of arthropods.

B. Physiological selectivity is a costly achievement. The costs involved in the research and development of pesticides are tremendous, well in the range of 20-40 million dollars per compound. If more of the highly specific pesticides are to be developed for integrated control, something probably will have to be done to offset those tremendous developmental costs to industry, for obviously the marketing potentials of selective and specific pesticides are much less than those of broad-spectrum compounds.

C. To make matters worse for industry, successful integrated control programs have resulted in smaller demands for pesticides and a reduced demand for broad-spectrum compounds. The continuation of this trend could deter industry from trying to find additional specific compounds with limited market potentials.

XII. Pest Management Conflicts (See Discussion)


Van Driesch & Bellows (1998) Account (Selective Pesticides)



Physiologically Selective Pesticides

Ecologically Selective Ways of Using Pesticides

Reduced Dosages

Selective Formulation & Materials

Treatment Area Limitation

Application Time Limitation

Redesigning the System

Creation and Use of Pesticide-Resistant Natural Enemy Populations

Conservation Philosophy


Physiologically Selective Pesticides. Van Driesche & Bellows (1999) observed that these pesticides are discovered by systematic testing to identify which of those available and effective for the control of the pests of the crop are also relatively harmless to the natural enemies to be conserved. Because populations of natural enemy species collected from different locations may differ in their susceptibility to a pesticide (Rosenheim and Hoy 1986; Rathman et al. 1990; Havron et al. 1991), susceptibilities must be measured for the local populations of natural enemies actually of interest. Also, information about effects of one pesticide is often not useful in predicting the toxicity of other pesticides to a given natural enemy or to other natural enemies (Bellows and Morse 1993). These facts dictate that only comprehensive local testing of pesticide-major natural enemy combinations can fully define which materials may be safely used in a crop (for spiders and brown planthopper on rice in the Philippines, see Thang et al. 1987). In western Europe, all pesticides are tested against eight standard species of natural enemies to partially characterize their likely risk to natural enemies (Van Driesche & Bellows 1999).

Test methods are sensitive to the precise conditions selected for the assay. Careful attention is given to standardizing the source, age, sex, and rearing history of the natural enemies used in tests, as well as the temperature, relative humidity, and degree of ventilation of the test environment, and the formulation, purity, and dosage of the test material (Croft 1990). The use of standardized assay conditions, such as those developed by the IOBC (International Organization for Biological Control) is critical if studies are to be compared (Hassan 1977, 1980, 1985, 1989a; Hassan et al. 1987; Morse and Bellows 1986). Basic to many such tests is the simultaneous testing of the pest organism under the same conditions as the natural enemies to determine whether differences in susceptibilities exist. Usually, pests are less susceptible to pesticides than are their natural enemies.

Methods for such screening range from laboratory tests, through semi-field tests to field studies. Laboratory methods include treatment of natural enemies through ingestion of pesticide or pesticide-treated materials, topical application, and placement of natural enemies on freshly dried pesticide residues on surfaces on which natural enemies are forced to rest. The slide-dip technique in which organisms are immersed in a pesticide solution is commonly used for tests with mites. Exposure to residues on test surfaces can involve glass, sand, or leaves as the test surface. Foliage may be sprayed in the laboratory or field, and used either immediately after drying, or after aging for various lengths of time under field or standardized laboratory conditions. Semi-field tests involve confining test organisms on parts of plants or whole plants, after treatment of foliage with pesticides. Field tests involve assessing impacts on natural enemy populations when whole fields or plots are treated with pesticide. In field tests, the use of small, replicated plots is often unsatisfactory because natural enemies are mobile and poor separation of treatment effects occurs. The use of large unreplicated plots, with repetition over time, often gives more satisfactory results (Brown 1989; Smart et al. 1989).

Methods used to express degrees of susceptibility to pesticide include the size of the dose that kills half of a sample of the test organisms (LD-50). Where organisms are not orally or topically dosed, but rather confined on a treated surface, the measure LC-50 is used, which is the concentration of solution applied to a treated surface that kills half of the test organisms in a defined period of time (usually 24 or 48 h), Tests which incorporate measurement of effects of pesticide residues of various ages (aged under either natural or defined environmental condilions) are especially helpful in defining the period of risk that particular species of natural enemies experience after a pesticide application (Bellows et al. 1985,1988,1992a, 1993; Morse et al. 1987; Bellows and Morse 1988). The ratio of the LC-50 values of the natural enemy and the pest, or that of the natural enemy to the recommended application rate for a pesticide is a useful comparative measure of the selectivity of a pesticide (Morse and Bellows 1986, Bellows and Morse 1993).

Assessment of natural enemy performance (ability to encounter and subdue prey successfully or, for parasitoids, to locate and oviposit in hosts) is a better indicator of the total effect of pesticide residues than is mortality because it also incorporates the sublethal effects of pesticides on natural enemies.

Ecologically Selective Ways of Using Pesticides. Pesticides can be used in various ways that reduce contact with natural enemies (Hull and Beers 1985).

Reduced Dosages. Effects of pesticides on natural enemies can be decreased by reducing the dosage applied (Poehling 1989). Use of half or quarter rates of pesticides often provides adequate pest control while reducing natural enemy mortality.

Selective Formulation & Materials. The physical characteristics of pesticide formulations influence their impact on natural enemies, Granular formulations applied to the soil, for example, do not contact natural enemies on foliage or in the air and hence many natural enemies are unaffected by such applications (Heimbach and Abel 1991). However, such materials are often designed for the purpose of producing pesticide residues in the topsoil and, in that zone, contact with natural enemies may be prolonged and extensive; such applications would be expected to significantly reduce susceptible natural enemy populations that live in the soil or forage on its surface (Van Driesche & Bellows 1999). Systemic pesticides do little direct damage to natural enemies which do not consume plant sap and thus do not contact the pesticide (Bellows et al. 1988). Pesticides that kill only if ingested, rather than by mere contact with the integument, are less likely to harm natural enemies (Bartlett 1966). Stomach poisons such as some pathogen-derived materials, plant-derived materials or mineral compounds are usually not damaging to predators and parasitoids which do not eat plant tissues. Nevertheless, even stomach poisons can be harmful to natural enemy populations if they cause drastic reductions in host or prey densities (Van Driesche & Bellows 1999).

Treatment Area Limitation. The extent of the area treated with pesticides can be adjusted to reduce exposure of natural enemies. For instance, the treatment of alternate rows instead of entire blocks in apple orchards controls mobile orchard pests, but allows greater survival of the coccinellid mite predator Stethorus punctum (LeConte) (Hull et al. 1983). DeBach (1958) successfully controlled purple scale, Lepidosaphes beckii (Newman), in citrus by applying oil to every 3rd row on a 6-month cycle. This provided satisfactory control of the pest without destroying natural enemies of other citrus pests. Velu & Kumaraswami (1990) found that treatment of alternate rows in cotton to provide effective pest control and, for some of the chemicals tested, enhanced parasitism levels of key pests. Contrarily, Carter (1987) found that strip spraying of cereals in Great Britain did not provide satisfactory control of aphids when strips were 12 meters wide because the natural enemies did not colonize the sprayed strips in time to suppress aphid resurgence.

Application Time Limitation. Contact between pesticides and natural enemies can be limited by using either nonpersistent materials, making less frequent applications, or applying materials in periods when natural enemies are not present or are in protected stages. Using nonpersistent pesticides reduces damage to natural enemy populations because natural enemies that emerge after toxic residues have declined (from inside protective structures such as cocoons or mummified hosts) can thus survive. Also, natural enemies that arrive from untreated areas can recolonize treated fields sooner. Persistence of pesticides varies greatly. Materials such as diazinon or azinphosmethyl leave residues on foliage and other surfaces for more than one week at levels that kill natural enemies. Some herbicides, such as the triazines, applied to soil last for months. Other materials, such as the insecticide pyrethrin, degrade in hours or days. Weather conditions affect persistence of pesticide residues. Rain is most important as it can wash residues off surfaces, and temperature may influence both the toxicity of the pesticide and the rates of dissipation and degradation of residues.

Adjustment of timing of pesticide applications to protect natural enemies is a matter either of reducing overall spray frequency so that there are times when the crop foliage is not toxic to natural enemies, or changing the exact timing of particular applications to avoid periods when natural enemies are in especially vulnerable life stags. Gage & Haynes (1975), e.g., used temperature-driven models of insect development to time pesticide applications against adult cereal leaf beetle, Oulema melanopus, treating after beetles had emerged, but prior to emergence of the parasitoid Tetrastichus julis (Walker). This system conserved the parasitoid, while the previous approach of direct pesticide-applications at the first generation of cereal leaf beetle larvae (the stage attacked by the parasitoids) did not. Efforts to redirect pesticide applications to periods when natural enemies are less vulnerable may require that natural enemy populations be monitored to determine when susceptible natural enemy stages are present, with the goal of creating pesticide-free times around critical periods. Monitoring methods have been employed to detect adults of some parasitoids to aid in their integration into crop management systems as, for example, with parasitoids of California red scale, Aonidiella auranti, on citrus in South Africa (Samways 1986) and parasitoids of San Jose scale, Quadraspidiotus perniciosus (Comstock), in orchards in North Carolina (U.S.A.) (Mc Clain et al. 1990). If many pesticide applications are required, it becomes increasingly difficult to avoid periods when natural enemies are in vulnerable life stages.

Redesigning the System. Options for the conservation of natural enemies are increased when the need for repeated use of broad spectrum pesticides is eliminated through the development of nontoxic pest control methods (such as use of natural enemies or other methods including traps, mating disruption with pheromones, and cultural methods). Reduced frequency of pesticide use in a crop is likely to greatly increase the survival and population densities of natural enemies, as in pear (Pyrus communis L.) orchards in Oregon, when mating disruption (based on pheromones) was substituted for organophosphate pesticides for control of codling moth, Cydia pomonella (L.). This substitution raised the densities of the predacious hemipteran Deraeocoris brevis piceatus Knight and the lacewing Chrysoperla carnea (Stephens), resulting in an 84% drop in densities of the pear psylla, Psylla pyricola F6rster, and a reduction of fruit contamination by honeydew from 9.7% to 1.5% (Westigard and Moffitt 1984).

Creation and Use of Pesticide-Resistant Natural Enemy Populations. Where pesticides are applied to crops and no sufficiently selective material or method of application can be discovered, attempts have been made to release and establish pesticide-resistant strains of key natural enemies. The intent of such releases is to permanently establish the pesticide-resistant form of the natural enemy so that pesticides may continue to be applied for other pests, while not disrupting control of the pest suppressed by the resistant natural enemy (Van Driesche & Bellows 1999).

Pesticide-resistant strains of several species of phytoseiid mites have been developed by laboratory selection or recovered from field populations, including Metaseiulus occidentalis (Nesbitt) (Croft 1976; Hoy et al. 1983; Mueller-Beilschmidt and Hoy 1987), Phytoseiulus persimilis (Fournier et al. 1988), Typhlodromus pyri and Amblyseius andersoni (Chant) (Penman et al. 1979, Genini and Baillod 1987), and Amblyseius fallacis (Whalon et al. 1982). Resistant strains of parasitic Hymenoptera have also been isolated from field populations and resistance levels to some pesticides further augmented by laboratory selection. Species have included an aphid parasitoid (Trioxys pallidus Haliday, Hoy and Cave 1989), a leaf miner parasitoid (Diglypbus begini [Ashmead], Rathman et al. 1990), and some scale parasitoids (Aphytis holoxanthus DeBach, Havron et al.and Aphytis melinus DeBach Rosenheim & Hoy l988).

Studies of these organisms have demonstrated that for many natural enemies genetic variability exists that permits the development of pesticide-resistant populations under field or laboratory selection. In several instances, it has been demonstrated that these strains can establish and survive for one or more years in commercial fields or orchards where pesticide applications are made (Hoy 1982b; Hoy et al. 1983; Caccia et al. 1985). initial establishment of resistant strains is fostered by prior destruction through pesticide application of any existing susceptible population of the same species (Hoy et al. 1990). Long term persistence of the resistant strain is needed if economic costs of strain development are to be offset by prolonged benefit. In some cases, such as the use of Phytoseiulus persimilis for mite control in greenhouse crops, no susceptible strain is present, and it is sufficient merely for the resistance to last for the life of the crop (usually 3-6 months), because new predators will be released in future crops (Fournier et al. 1988). In outdoor crops, maintenance of the resistant strain may require regular pesticide application. Where such applications are employed, introductions of pesticide resistant natural enemies can lead to their replacement of existing, pesticide-susceptible species (Caccia et al. 1985). In the absence of such ongoing pesticide usage, the introduced strain of resistant natural enemy may be displaced by other, pesticide-susceptible species (Downing and Moilliet 1972). The importance of the level and sustained nature of pesticide selection to the establishment of resistant strains of natural enemies in the field has been pointed out by Caprio et al. (1991). In some cases, the need for continued treatments in the field to retain resistance in natural enemies may be met by pesticide treatments made for other pests in the crop system, Trials in Great Britain with an organophosphate-resistant strain of Typhlodromus pyri showed survival of the predator in orchards treated with organophosphate insecticides at levels sufficient to control Panonycbus ulmi (Koch) and Aculus schlechtendali (Nalepa). In a pyrethroid-treated orchard this strain of T. Pyri was scarce and did not suppress pest mites (Solomon et al. 1993)

Conservation Philosophy. Effective conservation of natural enemies through either physiological or ecologically selective pesticides involves changes by growers in outlook as well as technological changes in procedure (Van Driesch & Bellows 1999). Crop production systems based on biological control seek to use pesticides as supplements to natural enemies, not substitutes for them. Emphasis on obtaining a high level of pest control from pesticide application is likely to be detrimental when biological control agents are part of the system. Pesticides can be integrated more effectively with natural enemies when used so as to inflict only moderate levels of mortality (30-600/o) on unacceptably high pest populations, when natural enemy action has been insufficient ( Legner 1970, 1987 , Legner & Olton  1968,  1970 ,  Legner & Sjogren  1984, 1985; Legner et al. 1974, 1975, 1981 ; Oatman 1962). If pesticides, of whatever degree of physiological or ecological selectivity, are used at rates and frequencies designed to provide the first and basic means of control, natural enemy populations are likely to be too disturbed by loss of their host or prey to provide any significant level of control in the system.




The social and economic factors which affect research and implementation of biological control were examined by Perkins & Garcia (1999). They state that the ability to predict and control organisms in a socially and economically desirable way is central to successful biological control strategies. Two considerations in biological control work are (1) a proposed biological control scheme manageable in a biological sense; that is, do the organisms behave in predictable and reliable ways; (2) can the organisms be manipulated in ways that are socially and economically feasible. This question raises issues in social sciences, politics and philosophy.

Although biological control researchers have had a history of successful practice, advocates of this approach to pest control believe their knowledge has not been fully utilized. Since the discovery of DDT's insecticidal properties in 1939, researchers in biological control have been sensitive to the competition with chemical control. They feel that the failure of biological control to be more widely adopted originates from social and economic issues rather than from a failure of biological knowledge. To explore how social and economic factors affect biological control it is necessary to define the meanings and scope of social and economic factors. Perkins & Garcia (1999) do this by outlining the political economic framework of biological control science. The definition of biological control itself is contested, and it is important to state clearly the definition used in an analysis.

Political and Economic Framework For Biological Control

Political economy examines the interactions between how resources are created, distributed and used, and the exercise of power and control. One can see the links between economic and political power that derive from ownership of factories and machines. The owners, either individuals or corporations, decide what will be made, how the product will be distributed and how the proceeds from the sales will be allocated. The power of ownership is not absolute, but compared to the work force the owners have more power within the boundaries of the manufacturing plant. This power and wealth can be used to influence the general political process of a country and is more influential than that exercised by the non-owner groups. Similarly, ownership of land creates power to make economic decisions that affect the welfare of the work force and of consumers of the lands' products. Owners of land tend to be wealthier than non-owners, and they exercise influence in the political process that is not available to non-owners (Perkins & Garcia 1999).

The creation and use of scientific and technological knowledge have attributes similar to the creation of other forms of wealth. Research and development occurs in laboratories and field stations that are owned and controlled by corporations, government agencies or universities. The researcher has more autonomy than a factory work, but this should not obscure the employer-employee relationship that exists between the working scientist and the laboratory administration. The ability of a researcher to work depends critically on convincing the administration that proposed research would yield a useful product, or knowledge that the administration wants to have created. Once developed, the scientific or technical knowledge may be owned and controlled by the administration. On the other hand, the knowledge may become part of the public domain and transfer to economic decision makers who have interest in and influence with the laboratory administration.

Pest control has been developed principally in agricultural research stations, public health laboratories and the private chemical industry. Biological control has been developed almost exclusively within agricultural research stations, which are supported by government and universities. Biological control information is largely non-proprietary and in the public domain. Although since 1980 some aspects of biological control knowledge have been developed by private, profit-seeking firms, the contributions of these companies are small.

Despite the free appearance of biological control knowledge, it would be wrong to assume that issues of power and control were not involved in the creation of this expertise or that future developments in biological control will be remote from questions about the exercise of political power. The allocations of budgets for agricultural research are highly politicized events (Guttman 1978, Rose-Ackerman & Evenson 1985). Some lines of research are favored over other, and political leaders in legislatures, executive branches and university administrations are sensitive to the demands of powerful constituents (Perkins & Garcia 1999).

Commercial agriculture is becoming increasingly competitive, and farmers, particularly in North America, have had productive capacities in excess of markets. The result is that farmers have been in an economic race to use the best technology to lower production costs and increase profits. Biological control must be applied to this highly competitive farm industry. Some research has addressed problems of urban, forest and public health issues, and such are expected to expand in the future. But, much of the political fortune of biological control will continue to be based on an ability to serve the farming industry. Individuals, partnerships, corporations, cooperatives or the state may control farming; but in each case they must behave as profit centers and atomistic entrepreneurs competing against other farm firms (Perkins & Garcia 1999). Other forms of pest control technology compete with biological control in the sense that farmers usually have options among several technical practices. Farm managers, legislators, executives and university administrators will be attuned to the abilities of biological control expertise to function commercially. The exercise of political power around biological control research will revolve about the abilities of the expertise to function within the economic framework of agricultural enterprise that produces for a competitive, global market.

Perkins & Garcia (1999) suggested that a political economic analysis of the creation of biological control technologies must examine several issues and events as follows: (1) Resources for scientific investigation must be allocated before scientific knowledge can be developed. Part of understanding how social and economic factors affect biological control involves understanding the resource allocation process for biological control research. The allocation process is political and influential parties try to direct research resources in ways that will protect and enhance their interests. (2) Once knowledge is articulated, questions arise about its usefulness. These questions center on the goodness of fit of the new technical knowledge to the complex of operations involved in agriculture. Is the technology cost effective? Can the user receive training and advice on how to use it? Is the new technology compatible with the user's other production practices? Does the new practice fit within the user's traditional activities. Does the new practice fit the habits of how the user relates to government authority, presumptions and traditions? Does the new user have to adopt new assumptions about nature or the state to feel positive about trying the new knowledge?

The Importance of Defining Biological Control.--Harry Smith (1919) defined biological control as follows: "The biological method of insect pest control... embraces the use of all natural organic checks, bacterial and fungous diseases as well as parasitic and predacious insects... From a practical stand point, the biological method may be arbitrarily divided into two sections: First, is the introduction of new entomophagous insects which do not occur in the infested region; and second, the increasing by artificial manipulation, of the individuals of a species already present in the infested region, in such a way as to bring about a higher mortality in their host than would have occurred if left to act under normal conditions."

Since 1919, researchers have expanded and refined the definition of biological control. Recently the scope and content of the definition have become important public policy issues. In 1987, the Committee on Science, Engineering and Public Policy (COSEPUP) of the National Academy of Sciences, National Academy of Engineering and the Institute of Medicine, advocated an expanded definition of biological control: "...the use of natural or modified organisms, genes, or gene products to reduce the effects of undesirable organisms (pests), and to favor desirable organisms such as crops, trees, animals, and beneficial insects and microorganisms." (COSEPUP 1987). This expanded definition has not been accepted by the Division of Biological Control, University of California, Berkeley, because the COSEPUP definition fails to provide essential and clear distinctions between different pest control technologies (Garcia et al. 1988), which are (1) self-sustaining control compared to control requiring continual input, and (2) density-dependent action characteristic of true biological control compared to the density-independent action of other suppression technologies. It was suggested that the essence of biological control was best described in a definition by DeBach (1964): "...the action of parasites, predators, or pathogens in maintaining another organism's population density at a lower average than would occur in their absence."

Difficulties Encountered in the Measurement of Biological Control.--It is impossible to know how social and economic factors affect research and implementation in biological control without knowing how these activities have fared in the past. Unfortunately, the ability to trace research and implementation in biological control are limited, especially when attempting to quantify the trends, as is discussed in other sections. It is possible to make quantitative estimates of research output and personnel levels in biological control for some periods and world areas. Quantitative estimates of research output, levels of research support and number of scientifically trained personnel engaged give only partial insights into the success of a scientific enterprise. Qualitative considerations are important to assessing a research area. Prominent governing factors are the goals and methods involved, the quality of training, morale, the location of the institutional base within the framework of power and the relationships between scientific personnel and their clients (pest control decision makers) who must ultimately use the knowledge generated.

The number of scientific papers published, personnel and amounts of funds expended on biological control research do not always indicate the quality of a research operation. Complex considerations surround our ability to understand the fate of biological control at the implementation stage. Biological control researchers have periodically issued compilations of "successes" sometimes as part of an effort to generate social and political support for their programs (DeBach 1974, Huffaker & Messenger 1976, Commonwealth Agricultural Bureaux 1980, Legner 1987 ). Unfortunately, social and economic information gathered in listing successful biological control events is limited to the amount of damage done by the pest before and after the biological agent was introduced. The difference between the before and after damages are then considered to be the value of the biological control agent. Such figures are often impressive, because some examples of biological control show enormous returns for small amounts of money invested.

Insights into the factors affecting the use of biological control, however, are difficult to draw from such studies because the behavior of all the organisms involved is not established and the interests of the pest control decision makers are often confounded with those of the biological control researcher. Such confusion is understandable because in classical biological control the researcher and the implementor are often the same person. If classical biological control were the only valuable mode of biological control then we would not be concerned with factors affecting decision makers such as farmers. Only the forces governing the amount of research in biological control would be considered because farmers would be the recipients of a new technology that is delivered to them without their having to take positive action. Augmentative and conservatory biological control, however, are now substantially shifting the form of biological control technology. Implementation of biological control through augmentation and conservation of natural enemies is virtually certain to require changed behaviors on the part of a pest control decision maker who is different from the researcher. In such cases the behavior and interests of the implementor must be distinguished from the scientist, or it will be impossible to analyze the factors affecting implementation. It must be known, for example, how the decision maker formulates long term goals. What sort of knowledge inputs are likely to appeal to the aspirations, experience and constraints within which the decision maker works? To what extent do economic factors interact with more subtle social, political and philosophical considerations? Failure to understand the actions of decision makers will lead to frustration for researchers and policy makers who believe that biological control offers substantial benefits.

Resource Allocation For Research

Trained personnel, supportive institutions and funds are required for research. Sources of public and private funds are primary social and economic factors affecting the research enterprise in biological control. Past performance indicates that the biological control research community is a vigorous and vital group generating new results, conceptual and methodological tools and successful control schemes. These indicators include (1) the output of literature in biological control, (2) the staffing levels in research organizations, (3) the signs of intellectual vigor in institutions essential to biological control research and (4) the introduction of exotic species in programs of classical biological control (see section on case histories).

Size of Research Effort.--It is difficult to estimate the size of the biological control research community and its productivity, as there is not tracking the number of scientists involved, their levels of productivity, the levels of funding provided and the number of projects completed. Some educated guesses may be obtained, however.

Abstracts of scientific papers, reports and books in biological control are published in Biocontrol News and Information (BNI), a publication of CAB International Institute of Biological Control (formerly the CIBC or Commonwealth Institute for Biological Control). BNI has been published regularly since 1980, and the number of abstracts published per year is the only global estimate available for the size of the worlds's biological control literature. The number of abstracts may be constrained more by budget limitations of CAB than by the number of literature entries available. The BNI database provides a minimal estimate of scientific activity in biological control. Since 1980 the average number of abstracts per year in BNI has been 2,421. (please see Anonymous 1985b, Perkins & Garcia 1999).

The some 2,400 literature messages which are produced in biological control per year is of interest because it allows a rough estimate of the number of scientist years involved in the biological control research enterprise. If it is assumed that one full time efficient scientist can produce 1-4 messages per year, then a production of 2,400 messages per year implies that the world has at least 600-2,400 scientist years working in biological control. Many personnel involved are part time in their research activities, so more individuals are involved than scientist years. In addition the estimate of 1-4 messages per year for the average scientists cannot be verified and some work in biological control does not result in publication. Judd et al. (1987) estimated the global resources for agricultural research to be 148 thousand scientist years in 1980. Research in biological control is thus about 0.4-1.6% of the total research in agriculture in terms of manpower allocations.

Agricultural science resources are not evenly distributed over the world, and historically agricultural research was conducted primarily in industrialized countries. In 1959, 19% of the manpower and 76% of the funds for agricultural research were spent in Europe, the U.S.S.R., North America and Oceania. By 1980, more rapid increases in third world agricultural research caused the proportion of resources expended by the industrialized world to drop to 57% of the manpower and 69% of the funds. Agricultural research is still an activity dominated by developed countries (Judd et al 1987, Perkins & Garcia 1999). It is not unexpected, therefore, that biological control researchers are concentrated in certain areas. A recent report of the U. S. Department of Agriculture estimated that ca. 190 scientist years were devoted to biological control work in the USDA laboratories and agencies (USDA 1985).

Biological Control and Pest Control Science.--A recent renaissance has been experienced in the biological control of insects. Perkins & Garcia (1999) suggest that biological control enjoyed a wave of rising popularity among researchers from 1920 to 1945 and then went into a decline, probably as a result of enthusiasm for research on the newly introduced synthetic organic insecticides. After a low in 1955, the fashion of doing research in biological control began to climb again, and the proportion of entomological papers now devoted to biological control is ca. 25%, which is about equal to the previous high of ca. 28% in 1940 (Anonymous 1981, Perkins & Garcia 1999).

Confirmation that enthusiasm for research on insecticides eclipsed biological control work was also noted by Price-Jones (1973) who sampled articles from the Journal of Economic Entomology. Similar conclusions were reached by Perkins (1978) in a study on how the introduction of DDT to the United States affected research by American economic entomologists. Perkins (1982) analyzed the changes in direction of one American research entomologist in the 1940's and 1950's and concluded that the technical capabilities of insecticides were responsible for a strong shift in research interests away from biologically based means of control towards chemically oriented technologies.

Biological Control Research Organization.--The proportion of entomological papers devoted to biological control has increased markedly since 1960 to over 2,000 per year (Anonymous 1985b). Before this time there were no more than 400 papers in biological control in any one year.

Developments in organizations and research also indicate that biological control is gradually being vitalized. The CAB International Institute for Biological Control is the largest multinational network of scientists engaged in biological control research. It was reorganized in 1985 to make it more useful to a wider range of clients (Anonymous 1985a). The Institute currently operates on ca. 1 million British pounds sterling per year (US $1.7 million), up 240% from its 1979 levels (CAB 1985). Many of the funds are expended for projects in developing countries and in Canada (CAB 1986, Perkins & Garcia 1999).

The U. S. Department of Agriculture is the world's largest agricultural research organization. It has made substantial changes in its biological control effort during the past 50 years. It had an active program of foreign exploration that was reduced during World War II. For 15 years no effort was made to revive the former program, but in 1955 plants to expand the work, primarily in augmentative biological control, were made. A major laboratory began operations in 1963 (Perkins 1982), and the USDA in the 1980's began a comprehensive effort to rationalize and coordinate biological control work (USDA 1984, 1985).

Another example of continuing vitality in biological control is seen in the number of publications appearing in Entomophaga, which has been published in France by the International Organization for Biological Control since 1956. This journal is supplemented by publications such as the Chinese Journal of Biological Control (since 1985) and Biocontrol News and Information (since 1980).

Expansion of Biological Control into New Study Areas.--There have been completely new industries and new areas of study begun since 1980 which increases the breadth of biological control. Some of the new companies supplying biological control agents are oriented towards the production and sale of long recognized biological control agents, such as Bacillus thuringiensis Berliner and Trichogramma spp. Other companies search for new agents and modify existing agents by genetic engineering (Anonymous 1985a, 1985c, 1985d, 1986, 1987, Hussey 1985, Perkins & Garcia 1999). Microbial agents now take less than 1% of the worlds's pesticide market (Anonymous 1985c), but interest shown by new companies suggests a bright future.

Three new areas of study have increased the scope of biological control research. In 1960 biological control research was almost entirely confined to the use of insects to control insect pests and, in a few cases, to control noxious plants. The methods used were largely those of classical biological control: foreign exploration for exotic natural enemies, importation of natural enemies, and release in the field followed by evaluation.

A few useful cases were known of the uses of pathogens to combat noxious plants (Andrés et al. 1976) and animal species (Weiser et al. 1976). Additionally, work before World War II had demonstrated the utility of indigenous natural enemies. Rudimentary ideas began to emerge during the 1930's and 1940's concerning the need to use insecticides in ways that would not interfere with the suppressive power of insect natural enemies. Nevertheless, the field of biological control was largely classical and research was oriented toward finding new natural enemies that would provide dramatic suppression of a pest comparable to that shown by the Vedalia beetle against the cottony cushion scale.

At least three new areas of research have developed since the 1950's: biological control of plant pathogens, use of pathogens for the suppression of weeds and insects, and integrated pest management (IPM). Plant pathogens to control weeds are an active area of research. A landmark monograph on the subject was published (Charudattan & Walker 1982), which unites the study of plant pathology, weed science and plant physiology. There were 55 projects cited involving the use of pathogens, including bacteria, fungi, nematodes and viruses. Five of these projects were considered operational. Control of skeleton weed in Australia by the rust fungus, Puccinia chondrillina Bubak & Syd, from the Mediterranean area, returned an estimated annual savings of $25.96 million. Water hyacinth control by Cercospora rodmanii Conway reached the stage of pilot tests by the United States Corps of Engineers in 1982.

A second new field is the use of biological control for the control of plant pathogens. A recent work by Cook & Baker (1983) noted that 20 years earlier only three examples of the use of antagonistic organisms to control plant pathogens could be cited, and 10 years earlier only six examples could be cited and only two were used commercially. The 1983 monograph had 1,081 references, 60% of which were post-1974. At the time of publication Cook & Baker had 15 key examples of successful applications of biological control of plant pathogens that could be illustrated in detail. The expansion of biological control into the field of plant pathology represents a new arena for biological control.

Integrated pest management which heavily involves biological control, is a promising approach. IPM as a pest control strategy was profoundly influenced by classical biological control (Perkins 1982), but it is doubtful that IPM's roots helped encourage research in biological control between 1960-1980. The U. S. National Science Foundation removed classical biological control from the large research project, "The Principles, Strategies and Tactics of Pest Population Regulation and Control in Major Crop Ecosystems," in favor of research on the ecological theory of why and how biological control works (Huffaker 1985). Thus, the first major research effort in IPM was handicapped by not building one of the component techniques for pest suppression into the basic design of the new research. Systems analysis and computer modeling were favored instead.

Combining biological control with pesticide use was the cornerstone on which the concept of integrated control was founded (Perkins 1982), but later definitions of IPM obscured the importance of biological control. The current definition of IPM does not mention biological control, or any other specific control technology explicitly: "Integrated pest control is a pest population management system that utilizes all suitable techniques in a compatible manner to reduce pest populations and maintain them at levels below those causing economic injury. Integrated control achieves this ideal by harmonizing techniques in an organized way, by making control practices compatible, and by blending them in a multi-faceted, flexible, evolving system;" (Smith & Reynolds 1967, Frisbie & Adkisson 1985).

In recent years, researchers have begun to ask whether biological control ought to be seen as fundamental to IPM, and to receive the funding levels appropriate to such a critically important technology. Some of these researchers believe biological control is fundament al to IPM but funding for biological control research is less than 20% of the total given to IPM. Most funds support pesticide timing, modeling of plant/pest interactions, defining the economic threshold, and predicting the size of pest populations (Hoy & Herzog 1985). Work on biological control must be built into IPM research from the beginning if biological control practice is to be successful. Tauber et al. (1985) state, "In many, if not most cases, biological control by itself, does not provide economically acceptable pest suppression in agricultural cropping systems. Therefore, biological control must be developed and implemented as a component of IPM. However, if it is to be an integral part of IPM (along with plant resistance, cultural methods and pesticidal controls) biological control must be nurtured to become a strong vital entity."

Important Factors Affecting Research in Biological Control.--There are many indications that biological control research of the mid to late 1980's is healthy and vibrant. Such indicators suggest that whatever factors govern the research in biological control, they are moving in favor of biological control. Complex social phenomena are impossible to attribute precisely to clear causes, but several seem particularly relevant since the early 1980's. Some arise from events removed from the activities of the biological control workers, but others are due to the activities of the research community.

Scientific research requires resources, so it is not surprising that the amount of research in biological control is highly correlated with the gross domestic product (GDP) of a country. Perkins & Garcia (1999) presents the GDP of 58 countries, each of which produced at least one paper in biological control, of which an abstract was published during the 1984-86 period. The data suggests that countries with an annual GDP of $10 billion will publish about 9.5 papers in biological control every three years, or 3.2 papers per year. Alternatively, for $2.3 billion of annual GDP, it would be expected to see one paper in biological control published each year. Productivity of research in biological control correlated with GDP indicates that this form of research is similar to others in the sense that wealthy countries do more of it. Correlation between a country's wealth and its research productivity does not, however, reveal everything about the ways in which each country may decide how much and what kind of biological control research to perform. Moreover, the data suggest that some countries are particularly high in their productivity of biological control research given their GDPs (e.g., Canada, Australia and India), while others may be low in output compared to their GDP's (e.g., Japan, Germany and France).

Explanations for why some countries are high producers compared to others are not obvious, but one possibility is that membership in an international network such as CIBC is conducive to productivity in biological control research. Therefore, countries such as Australia, India and Canada, all long term members of Commonwealth Institute of Biological Control, are comparatively high. Conversely, countries that are not in coordinated networks may have research productivities considerably below what the sizes of their economies might suggest. France and Japan have GDP's 2.5 and 4.4 times the size of Canada's GDP, respectively, but these two countries have research outputs of 0.67 and 0.79 the size of Canada's respectively. Canada's membership in CIBC may be the cause of its higher research output (Perkins & Garcia 1999).

Another possibility to explain high interest in biological control in countries like Canada and Australia is that both areas were subject to European invasion. European people brought their insect and weed pests (Crosby 1986). Much biological control work in these areas has been an effort to reassociate imported pests with natural enemies. Europe, in contrast, has had fewer invasive pests and therefore may be an area where classical biological control has less success (Perkins & Garcia 1999).

Environmental concerns about pollution potential from pesticides or from the failure of chemical control through resistance and destruction of natural enemies may also affect research allocations for biological control. Malaysia has recently shown interest in biological control for conservation purposes, despite some anxiety about introducing exotic pests (Perkins & Garcia 1999). Other positive experiences with integrated pest management in Malaysia nevertheless date to the 1960's (Conway 1972). Similarly Indonesia has an official government policy to encourage implementation of IPM and conservatory biological control, due to concerns about insecticide-induced outbreaks of the brown plant hopper on rice. Problems with shortage of foreign exchange to import chemicals has also been a factor in Indonesia and elsewhere (England 1987, Repetto 1985, Perkins & Garcia 1999).

Interest in environmental protection has created barriers to research in biological control. Ecologists and the public realize that the introduction of any new agent, even beneficial, can have undesirable outcomes. Capabilities of producing genetically engineered agents have complicated this issue further. Consequently biological control researchers must now contend with regulations from which they were previously exempt, such as the Endangered Species Act, the National Environmental Protection Act, and the Federal Food, Drug and Cosmetic Act (Coulson & Soper 1992, Waage & Greathead 1987).

The Political Economy of Biological Control Research & Research Needs

Studies are required to determine how social and economic factors affect the allocation of resources to biological control. Factors likely to be of importance are the philosophical world views prevalent in the research community, the political strength and organization of agriculturalists, the nature and size of the agricultural economy, the research activities of neighboring countries and the political currents favoring environmental protection. Judd et al. (1987) analyzed socio-economic factors determining research investments in agricultural science, but it is not possible to make predictions about the factors affecting research in biological control.

An examination of the agricultural research establishment of each country could indicate ways in which biological control research could be enhanced, given the specifics of the individual country. Factors affecting research, both positive and negative, need analysis on a country-by-country basis. Recent events offer challenges to increasing research in biological control, particularly on weeds. The basic conflict is that one person's weed may be another's valuable crop plant. To illustrate this, Australian court injunctions recently blocked the importation of insect control agents for the plant Echium plantegineum (L.). Livestock interests know E. plantagineum as "Patterson's Curse," but beekeepers call it "Salvation Jane." The popular names imply strongly differing attitudes toward the plant (Waage & Greathead 1987).

A commercial biological control industry based on release of mass-produced pathogens, parasitoids and predators, indicates other factors may be important in the future: patents, taxes, commercial policies and laws. Countries encouraging the entrepreneurship of biological control manufacturers, through policies favorable to their enterprises or through direct subsidies, may find that the manufacturers make significant additions to research in biological control.

Socio-Economics of Biological Control

               Investment.--There is a problem which stems from the fact that the actual or potential users of biological control products number in the hundreds of millions of individuals, including all the farmers of the world and other decision makers who have responsibilities for protecting society from pests. The research community in contrast is small with numbers limited to a few thousand individuals. Furthermore, researchers deliberately leave a trace of their activities via publication, but farmers and pest control decision makers usually leave no written record of their actions, certainly not a publica record that is easily accessible for review.

Pest control decisions are also complex, and are made for the private benefit of the decision makers. Some, however, are made by officials in public agencies for the public benefit. Therefore the social and economic factors affecting the choices made by the decision maker are complicated by the nature of the institution in which the decision maker works. Another complication in assessing the degree of implementation in biological control emerges from the complexity of the technology. Each of the three categories of biological control (classical, augmentative, conservatory) will probably have different factors affecting their respective implementations.

A theoretical model of the relevant social and economic factors may be constructed. The most useful perspective on the subject begins with the recognition that if someone decides to use biological control, then he has chosen a particular technology to achieve specific material ends. The choice is made in the context of alternatives ranging from doing nothing to selection of another way of mitigating the damage from the pest. A conscious decision to adopt biological control is an investment decision, i.e., an action based on choice in which the decision maker expects a return, presumably a return that is better than could be expected from other technology choices. The return could be monetary or have a high monetary component. Nonmonetized and nonmaterial returns could also be important to the decision maker.

When use of biological control is perceived as an investment decision, the factors affecting the use of the three categories of biological control appear different in terms of the risks accepted by the decision maker. Classical biological control is the lest problematic for the researcher and the farmer or public. If an introduced exotic control agent has been screened for adverse properties, the only monetary risks involved are the costs for exploration, shipment, quarantine and release. If the organism succeeds in its new context, then most likely it will return substantial rewards over a period of years for a relatively small investment. Moreover, most classical biological control is conducted by the state, so the individual pest control decision maker bears no personal financial risk. In many cases the individual grower may not be consulted about the decision to release an exotic agent because the research community bears full responsibility and power to identify pests, seek solutions and implement them as part of a research implementation program. The activities are all research until the introduced organism demonstrates its effectiveness. DeBach (1974) and Coulson & Soper (1991) argued that the returns from this sort of biological control research and development have been extraordinarily high compared to the amounts spent on biological control research, including expenses for those introductions that resulted in no significant suppression of the pest.

Classical Biological Control.--The close relationship between classical biological control and the research enterprise makes the factors affecting implementation of classical biological control likely to be identical to those affecting biological control research generally. The larger the economy the more likelihood that classical biological control research and implementation will be accomplished. However, size of the economy cannot be the sole determinant of the efforts invested in classical biological control. Decisions within the research community could lead to resources going into augmentative or conservatory biological control research rather than classical. Additionally, classical biological control requires either foreign exploration or collaboration with foreign scientists who agree to ship exotic organisms. Political relationships between countries therefore can influence the fortunes of classical biological control research.

Augmentative Biological Control.--Practical schemes for artificially releasing a large number of controlling organisms to attack a pest are inevitably dependent on the scale of industrial culture of the controlling organism. The agents are packaged, sold and dispersed much as a pesticide produce. Factors affecting use of such a produce are not different from those affecting the use of a pesticide: cost, ease of use, effectiveness, safety and ability of the agent to integrate easily with other parts of the operation.

Conservation.--The preservation of natural enemies present in the environment is a problematic investment from the viewpoint of the individual pest control decision maker. Perhaps the difficulties can best be explained by reference to a typical situation in IPM. A natural enemy present in the farmer's fields provides less suppression of a pest because pesticides or cultural practices destroy or otherwise disfavor expression of the natural enemies. If the grower would alter existing practices the natural enemy population might provide a higher level of suppression of the pest, perhaps enough to obviate the need for other pest control measures. Two events must occur to make use of the existing natural enemy complexes. First, the grower must stop destroying the effectiveness of the existing natural enemies. Unfortunately, alteration of existing practices may open the grower's entire mode of operation of risk or loss or severe disruption. Ending the use of a pesticide, for example, could expose the grower to losses from a pest which might be prevented by the preserved natural enemies. Therefore, the grower must have confidence that the foregone practice will not result in devastating losses. Secondly, the grower must monitor the pest and natural enemy populations to ensure the pests are suppressed.

Some studies have examined the inclinations and abilities of farmers to adopt IPM schemes, most of which have a component of conserving natural enemies (Wearing 1988). Peanut farmers in Georgia evidence reluctance to shift to IPM despite objective data indicating that the new technology was more efficient than conventional pest control (Musser et al. 1986). Georgia cotton growers received no increase in net returns from IPM (Hatcher et al. 1984), so the attractiveness of this technology for them was slight. Adoption of IPM by Iowa growers was related to opinion leadership an adoption orientation, and prior knowledge of IPM. In turn, these variables were positively related to income, education, farm size, and attitudes towards chemicals (Salama 1983). One citrus grove manner in California reported having saved $500-600/ha. by using IPM rather than chemicals alone (Hardison 1986). He reduced pest control costs from 35-40% and cash production costs to 8%

Marking studies have shown that lady beetles, lacewings, syrphid flies and parasitic wasps fed on nectar or pollen provided by borders of flowering plants around farms. Many insects were shown to have moved 250 ft. into adjacent field crops. The use of elemental marker rubium also showed that syrphid flies, parasitic wasps and lacewings fed on flowering cover crops in orchards and that some moved 6 ft. high in the tree canopy and 100 fleet away from the treated area. The use of nectar or pollen by beneficial insects helps them to survive and reproduce. Thus, planting flowering plants and perennial grasses around farms may lead to better biological control of pests in nearby crops (Long et al. 1998).

Risks for adopting conservatory biological control may be particularly high when the crop's price depends on cosmetic quality. Fenmore & Norton (1985) analyzed the economics of the production of English dessert apples and the potentials for adopting conservatory biological control rather than calendar-based chemical applications. They concluded that the recent price history of these apples is such that a farmer would be taking a grave risk to switch from automatic sprays to IPM. As little as a 1-2% shift of the crop from cosmetically perfect to damaged but usable fruit would be sufficient to eliminate all savings of the costs of insecticides obtained from IPM practices. This case study exemplifies the concept that pesticides provide cheap insurance against catastrophic economic losses, even when an argument can be made that the chemicals are not needed on biological grounds.

Crops that are not heavily dependent upon cosmetic quality may be better candidates for conservatory biological control. Masud & Lacewell (1985) analyzed adoptions of IPM in southern and southeastern United States cotton production. They concluded that various alterations in production practices, including IPM, could reduce insecticide use and produce significant savings at an acceptable level of risk. Burrows (1983) also concluded that IPM could reduce pesticide use in California cotton production by 31%.

These examples do not necessarily mean that biological control will have little utility on crops in which cosmetic quality is important. Examples from many countries demonstrate the success of biological control, usually classical, in fruits such as citrus, apples and olives (Huffaker & Messenger 1976, Hardison 1986). The critical factor may lie in the notion that if biological control is extremely effective, then it may be readily adopted. Cases in which the natural enemy is not as effective so that management is still required by the grower, may be more difficult to adopt. Entomological researchers may correctly argue that suppressive power is available from the natural enemy, but a grower less skilled in entomology and dependent upon each year's crop for his livelihood, will see the situation differently. Alternatively, biological control may be useful on crops in which cosmetic quality is important provided the pest does not attack the marketed portion of the plant directly (Perkins & Garcia 1999).

Under some circumstances factors transcending the individual decision maker may become of paramount importance. The attitudes and knowledge of the individual pest control decision maker may be immaterial to the ability of a particular biological control technology to function. examples of these transcendent considerations include how the pest control decision makers are organized and relate to each other and to their supporting scientists; the relationships between the decision makers and the authority of the state; and the nature of the market for the decision maker's produce. Swezey & Daxi (1983) argued that little headway could be made on the development of IPM practices for Nicaraguan cotton until after the Samoza government was overthrown in 1979. Earlier the political and economic structures of Nicaragua were conducive to overuse of pesticides.

The effectiveness of an IPM scheme may depend upon cooperation among farmers. When some farmers spray insecticides, the drift may destroy the natural enemies being conserved by other farmers. Under such circumstances an individual grower would be powerless to adopt biological control without convincing all growers in the area that they, too, should conserve their natural enemies by not spraying. This situation is probably well illustrated in the lower San Joaquin Valley of California where diverse cropping systems intermingle, and spray drift is a widespread occurrence.

Collaboration between growers may be more difficult to achieve than convincing individual growers to conserve their natural enemies. An apparently simple question of technological choice by a farmer may be a more complicated matter involving the question of social and political relationships among growers in a particular region.

Habitat Alteration.--  A notable case is the successful habitat reduction for houseflies that breed in decaying melons in the American Southwest (Legner & Olton 1975, Olton & Legner 1973).  The simple procedure of breaking-open culled melons at harvest accelerated decay of the breeding source and greatly reduced fly breeding.  Another example is the elimination of breeding sites for the Australian bush fly, Musca sorbens, in the Marshall Islands by reducing the number of unleashed dogs on the islands as well as the institution of an effective adult fly baiting procedure (Legner et al 1974. )


Pest Managment Conflicts -- See Discussion




Perkins and Garcia (1999) concluded that biological control has a place in the most modern and sophisticated of pest control technologies, but researchers and advocates of the technology must be sensitive to the factors working against an easy transition to more reliance on biological control. Failure to be realistic about the social and economic factors weighing against use of biological control might actually be detrimental to the research enterprise. Despite the problems, several biological and cultural trends could improve biological control technology. An understanding of these trends could promote research and use of biological control in many areas of the world.

Biological considerations of importance to biological control include problems associated with the use of pesticides, particularly insecticides: resistance, destruction of natural enemies accompanied by pest outbreaks, and damage to the health of humans and nontarget organisms. Rachel Carson's Silent Spring (Carson 1962) presented the first analysis of these problems, but many policy studies since her landmark work have confirmed the accuracy of her thoughts.

Pesticide resistance and destruction of natural enemies make chemicals technologically ineffective for the pest controller, thus providing an incentive to look elsewhere for relief from pest damages. Harm to non-target organisms leads to more stringent regulations, which places the pest controller under severe political pressure to find an alternative. In either case the biological control researcher can find an opportunity to provide a less dangerous mode of pest control, and the client audience of pest controllers will be a willing audience. Cultural factors affecting the fortunes of biological control are more complex than the biological considerations. The most important trends can be grouped into two main categories: regulatory and pricing.


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