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INTRODUCTION AND SCOPE OF BIOLOGICAL
PEST CONTROL
Dr. E. F. Legner, University of California, Riverside (Contacts) 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. 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 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. 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. |