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
only.
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 - -
|
|________________________________________________________________
T
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
ecology.
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.
REFERENCES:
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.
