A SYNOPSIS OF THE PESTICIDE PROBLEM
B. PESTICIDES A S TOOLS FOR ECOLOGICAL RESEARCH
121
Most of the research which has involved the use of pesticides has
been done to discover their effects, but pesticides have potential value as
research tools in solving ecological problems unconnected with pesticide
use. For example total weed killers may be preferable to fire or mechanical methods for removing vegetation in studies on succession.
Pesticides which kill predatory insects have been used to kill predators in order to study their role in regulating the numbers of certain
prey species (Huffaker and Kennett, 1956). Satchel1 and Mountford
(1962) used phosdrin to discover the numbers of Tortrix larvae occurring
on oak trees. They injected the insecticide into the oaks and collected
the dead larvae which fell on to the sheets placed on the ground round
the trees. Selective pesticides are potentially the most ecologically useful tools, for they enable, or would enable, workers to “dissect” ecosystems; other methods of collecting out such as shooting, trapping or
collecting by hand are usually prohibitively expensive in time, labour
or money. The author and his colleagues have used dieldrin to test the
hypothesis that the millipede Glomeris is a key species in Brachipodium
pinnatum grassland (Davis et al., unpublished). Dieldrin was applied at
a level which killed all the Chrneris on the experimental plots but had
little or no effect on other arthropods of similar size or habit. So far
the elimination of the millipede has not led to any discernible changes
in the vegetation. Another millipede appears to have become commoner
since the treatment and so a possible explanation is that it has taken
over the role of the Glomeris. Alternatively it is possible that neither
Qlmeris not its successor are important in the maintenance of B. pinnatum grassland. Dieldrin, like most pesticides in common use, has
differential effects but it has a great disadvantage in that it is not
truly specific. A truly specific pesticide would have considerable value
as a research tool, especially in studying competitive relationships and
the ecological significance of key species.
In some instances pesticides could be used like radioactive tracers to
study food chains and preylpredator relationships.
IX. CONCLUSIONS ON PESTICIDE EFFECTS
A. COMPARISONS WITH OTHER FACTORS
We have seen that pesticides can have many different types of effect
but since these are usually independent of density they do not normally
control populations in the manner of density-dependent factors like
disease and availability of food. Total weed killers,-by killing the whole
flora and fauna, resemble fire in their general effect. Pesticides which
kill all animals resemble freak natural conditions like excessive cold
B. PESTICIDES A S TOOLS FOR ECOLOGICAL RESEARCH
121
Most of the research which has involved the use of pesticides has
been done to discover their effects, but pesticides have potential value as
research tools in solving ecological problems unconnected with pesticide
use. For example total weed killers may be preferable to fire or mechanical methods for removing vegetation in studies on succession.
Pesticides which kill predatory insects have been used to kill predators in order to study their role in regulating the numbers of certain
prey species (Huffaker and Kennett, 1956). Satchel1 and Mountford
(1962) used phosdrin to discover the numbers of Tortrix larvae occurring
on oak trees. They injected the insecticide into the oaks and collected
the dead larvae which fell on to the sheets placed on the ground round
the trees. Selective pesticides are potentially the most ecologically useful tools, for they enable, or would enable, workers to “dissect” ecosystems; other methods of collecting out such as shooting, trapping or
collecting by hand are usually prohibitively expensive in time, labour
or money. The author and his colleagues have used dieldrin to test the
hypothesis that the millipede Glomeris is a key species in Brachipodium
pinnatum grassland (Davis et al., unpublished). Dieldrin was applied at
a level which killed all the Chrneris on the experimental plots but had
little or no effect on other arthropods of similar size or habit. So far
the elimination of the millipede has not led to any discernible changes
in the vegetation. Another millipede appears to have become commoner
since the treatment and so a possible explanation is that it has taken
over the role of the Glomeris. Alternatively it is possible that neither
Qlmeris not its successor are important in the maintenance of B. pinnatum grassland. Dieldrin, like most pesticides in common use, has
differential effects but it has a great disadvantage in that it is not
truly specific. A truly specific pesticide would have considerable value
as a research tool, especially in studying competitive relationships and
the ecological significance of key species.
In some instances pesticides could be used like radioactive tracers to
study food chains and preylpredator relationships.
IX. CONCLUSIONS ON PESTICIDE EFFECTS
A. COMPARISONS WITH OTHER FACTORS
We have seen that pesticides can have many different types of effect
but since these are usually independent of density they do not normally
control populations in the manner of density-dependent factors like
disease and availability of food. Total weed killers,-by killing the whole
flora and fauna, resemble fire in their general effect. Pesticides which
kill all animals resemble freak natural conditions like excessive cold