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Dr. E. F. Legner, University of California, Riverside





Since 1900 the partial, substantial and complete biological control of a large number of insects, mites, weeds and mammals has been attained in over 70 countries.  As an adjunct to other methods, it is safe, effective and usually permanent.  Emphasis on the biological control method can act to restore the erosion of the human environment by deemphasizing such disruptive methods of pest control as some cultural practices, and notably the use of broad-spectrum pesticides.


California took an early lead and continues to be one of the major centers for biological control work.  By 1961, approximately 1/3d of all the beneficial insects established in the continental United States had been introduced by California-based organizations. --- During the 1980's and early 1990's UC Riverside and Berkeley have maintained a total of about 18 full-time professional staff plus several emeriti, and about 10 research associates, and graduate students that vary from 10-20.


On a national scale, the U. S. Department of Agriculture employs varying numbers (25-40) of entomologists in biological control work, depending on active programs.  On the world scene, it is estimated that there are aver 300 entomologists engaged in classical practical biological control work.  This does not include persons engaged in fundamental research only.




Some examples of individual projects give fairly accurate figures for the damage caused by a pest of and the cost of biological control work as follows:


Permanent control of the coconut scale, Aspidiotus destructor, on the Portuguese Island of Principe off the west coast of Africa was achieved by the introduction of the coccinellid predator Cryptognatha nodiceps from Trinidad in 1955.  Losses in copra production, the principal crop of Principe, caused by the coconut scale were estimated at 900 tons annually, which was then worth about #72,000 (English pounds).  At a cost of #200, Cryptognatha was collected and shipped to Principe by the CIBC, which also supplied an entomologist who for one year bred the predator, supervised its release, establishment and spread, etc. at an additional cost of #3,500.  The total cost of this project, therefore, was about #3,700.  The financial return from the complete control has been about #1,000,000 as of 1970, or a 1,800% return per annum.  Not a bad investment!


The sugar cane moth borers, Diatraea spp., have been very successfully controlled in certain areas of the West Indies and South America by introduced natural enemies.  For example, in Antigua the cost of liberations of Lixophaga diatraeae during 1931 and 1945 was about #8.500.  The case return from this project in terms of increased sugar at the factory and increased yields in the field has been about #16,000 annually since 1934, or about 200% per annum and about #552,000 to 1961.  The later acquisition of Apanteles flavipes Cameron from India further increased the magnitude of biological control so that savings soared beyond this level.  On the island of St. Kitts, where permanent control was achieved, the total cost of introducing Lixophaga in 1934 was #200.  The resulting benefits have accrued to about #50,000/annum or #1,700,000 by 1970, a return of 15,000% per annum!


There are many other examples where estimates are not so simple.  Evaluation of the worth of many of the successes listed in Chapters 23 & 24 of the DeBach (1964) text is, unfortunately, impossible.   Chapter 1 of the DeBach (1964) shows a rough balance for biological control work carried out in California for the interval 1923-1959.  Considering a total budget outlay of about $4,300,000 against about $115,800,000 benefits realized from just five successful biological control projects, the citrophilous mealybug, the black scale, the grapeleaf skeletonizer, the spotted alfalfa aphid and the Klamath weed, it is obvious that the economic returns from funds invested have been of the nature that any businessman would consider extremely satisfactory.  An estimate of the present benefits being derived from these five successes are running about $10,000,000 annually, not to mention the reduction of pesticidal threats to the environment.


It must be kept in mind that many more than five successes are registered, but economic data is difficult to derive.  However, this does indicate that biological control, though by no means a panacea for all our pest problems, can be a sound investment and extremely profitable venture.


Important Terms


Natural Enemies (predators, parasitoids, pathogens, parasites.  Organisms that prey upon other organisms, parasitize them, or cause disease).  Predators are organisms that consume more than one host individual or prey during the course of their development.  Predators are usually free-living in all stages except the egg stage.  They kill and consume their prey either immediately or within a relatively short period of time.  Some predators feed indiscriminately upon various developmental stages and kinds of prey; other are more selective.  Parasites are organisms that live within the body of their hosts without killing the host, but usually debilitating them to various degrees.  Parasitoids are insects that reach maturity by developing upon a single host individual, eventually killing same.  Three insect orders contain many species that have adopted the parasitoidal habit, namely Hymenoptera, Diptera and Strepsiptera, with Hymenoptera being the largest representative.  Pathogens include viruses, bacteria, protozoa, fungi and nematodes.  They cause diseases of arthropods.


Biological Control is a term that has been used both in a fundamental ecological sense and in the utilitarian sense to designate a field of human endeavor.  Originally, the term was defined for use in the applied sense.  Biological control can be considered a phase of natural control or limitation.  Natural Control is the balance of nature, natural balance, population balance or what Darwin called "the struggle for existence."  Natural control has also been considered as "The maintenance of a fluctuating population density of an organism with certain definable upper and lower limits over a protracted period of time, by the action of abiotic and biotic environmental factors."


If we plot the density of any organism (D) against time (T), we see that over a protracted period of time its population density will fluctuate within certain limits and about a characteristic mean density, that of its general equilibrium level.


Natural control is essentially permanent in the absence of gross permanent environmental changes.  It is characteristic of all plant and animal populations on the face of the earth.  Therefore, "biological control" can be considered as representing the action of natural enemies (biotic factors) in maintaining another organism's population density at a lower average level than would occur in the absence. 


In 1919, Harry Scott Smith <PHOTO> first used the term biological control to denote "the utilization of organisms for the control of population densities of animals and plants."  Since then many definitions have been offered, generating considerable discussion and argument.  Some expand the meaning to cover such things as breeding resistant plants and genetic engineering.


An extreme case was presented by Pollard in the 1966 Bulletin Entomological Society of America:  "Parasites, predators, viruses, bacteria, fungi, nematodes, pathogens, birds, mice, skunks, fish.....heat, light, sound, genetics, metabolism, X-rays, laser beams, chemosterilants, nutrition, attractants, sex lures, gamma irradiation, diapause and ecology.


The simplest definition was given by the International Biological Program:  "Using biota to control biota."  Jost M. Franz of the Institut für Biologische Schädlingsbekämpfung offered the following modification of Smith's definition in his 1961 text:  "Biological control denotes the active manipulation of antagonistic organisms by man to reduce pest population densities, both plant and animal, to non-economically important levels."


Autocidal Control is the mass release of artificially sterilized or genetically inferior individuals which are used to inundate and possibly eradicate geographically isolated pest populations.


Other Controls include chemical, cultural, resistant varieties of crops and legislative control (quarantine)


The modern approach to pest control considers, and in various ways utilizes, all of the eight kinds of control.  As a result we have gravely suffered in the execution of the classical approach in that only a fraction of the control research funds has been spent on it during the past several decades.  Hopefully we are entering a new era of awareness and will elevate the classical approach to a higher priority, since history shows that it nest the greatest permanent effects in pest control.


               Other texts and files in this series may be viewed by CLICKING on the following:


              Secrets of Science  <museum1.htm>

History of Biological Control  <museum2.htm>

Introduction and Scope of Biological Control  <museum3.htm>

National and International Organizations Active in Biological Control  <museum4.htm>

Economic Gains and Analysis of Successes in Biological Control  <museum5.htm>

Trends and Future Possibilities in Biological Control  <museum6.htm>

Beneficial Insects  <museum7.htm>

Case Histories of Salient Biological Control Projects   <detailed,htm>

Guide to Identifying Predatory and Parasitic Insects  <NEGUIDE.1>, <NEGUIDE.2>... etc.

Insect Natural Enemy Photos  <NE-2ba.PCX>, <NE-2bb.PCX>...  <NE-247ba.PCX>... etc.


          Special Reports

                Meal Worm Project  <project.3.htm>

             Ladybird Beetles  <ladybird.htm>

             Fruit Flies in California  <fruitfly.htm>

             Killer Bees  <killer.htm>

             Monarch & Viceroy Butterflies <31aug95.mus.htm>

             Everywhere is Home <9feb98.mus.htm>

             Familiar Butterflies of the United States & Canada <butterfl.htm>



References:   Please refer to  <biology.ref.htm>, [Additional references may be found at:  MELVYL Library]


DeBach, P. (ed.).  1964.  Biological Control of Insect Pests and Weeds.  Reinhold Publ. Co., New York.  844 p.


Franz, J.M.  1961.  Biologische Schädlingsbekämpfung.  Paul Parey, Berlin & Hamburg.  302 p.


Nicholson, A. J.  1933.  The balance of animal populations.  J. Anim. Ecol. Suppl. 2:  132-78.


Pimentel, D.  1966e.  Beneficial insects.  Ecology (1966).  p. 162-63.


Simmonds, F. J.  1967.  The economics of biological control.  J. Roy. Soc. Arts 115:  880-98.


Smith, H. S.  1919.  On some phases of insect control by the biological method.  J. Econ. Ent. 12:  288-92.


Smith, H. S.  1929.  Multiple parasitism:  its relation to the biological control of insect pests.  Bull. Ent. Res. 20:  141-49.


Smith, H. S.  1935.  The role of biotic factors in the determination of population densities.  J. Econ. Ent. 28:  873-98.