FILE:  <emt129.1.htm>    Comprehensive Account                                                                                                                  <Navigate to MAIN MENU>






I.  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.


A.  as an adjunct to other methods, it is safe, effective and usually permanent.


B.  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.


II.  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.


--- UC Riverside and Berkeley had a total of about 18 full-time professional staff plus several emeriti, and

about 10 research associates, and graduate students that varied from 10-20 until the 1980's.


III.  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.


IV.  On the world scene, it is estimated that there are over 300 entomologists engaged in classical

       practical biological control work.  This does not include persons engaged in fundamental research



V.  Economics


     Some examples of individual projects give fairly accurate figures for the damage caused by a pest of and the

cost of biological control work.  This subject is treated in greater detail in Section 14.


A.  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!


B.  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!


C.  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. 


D.  Chapter 1 of that text 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.


VI.  Important Terms


A.  Natural Enemies (predators, parasitoids, pathogens, parasites.  Organisms that prey upon other organisms,

     parasitize them, or cause disease).


1.  predators = 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.


2.  parasites = organisms that live within the body of their hosts without killing the host, but usually debilitating

     them to various degrees.


3.  parasitoids = 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.


4.  pathogens = viruses, bacteria, protozoa, fungi and nematodes.  They cause diseases of arthropods.


B.  Biological Control


1.  The text distinguishes biological control used in a fundamental ecological sense and in the utilitarian sense to

     designate a field of human endeavor.


2.  Originally, the term was defined for use in the applied sense.


3.  Biological control can be considered a phase of natural control or limitation.


4.  Natural Control = balance of nature, natural balance, population balance or what Darwin called "the struggle

     for existence."


a.  Natural control is "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."


b.  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.




| - - - - - - - - - - - - - - - - - - - - - - - - - - - - upper limit- -


        D    |_____________________________________ General Equilibrium Level



|- - - - - - - - - - - - - - - - - - - - - - - - - - - - -lower limit - -






c.  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.


5.  Therefore, "biological control" can be thought of 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. 


6.  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.


a.  Some expand the meaning to cover such things as breeding resistant plants and genetic engineering.


b.  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



c.  The simplest definition was given by the International Biological Program:  "Using biota to control biota."


d.  Jost M. Franz <PHOTO> 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."


C.  Autocidal Control = the mass release of artificially sterilized or genetically inferior individuals which are used to

     inundate and possibly eradicate geographically isolated pest populations.

D.  Chemical Control.


E.  Cultural Control.


F.  Resistant Varieties of Crops.


G.  Legislative Control (Quarantine).


VII.  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.





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.


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.