A SYNOPSIS OF THE PESTICIDE PROBLEM
125
X. SUMMARY
The pesticide problem is essentially ecological and an interdisciplinary
approach to it is essential. Pesticides always affect ecosystems although
they are usually applied to control single or very few pest species. Conclusions about pesticide effects on populations must generally remain
tentative owing to the lack of information on population dynamics,
feeding habits and toxicology. Most pesticides are non-specific in their
action and their effects are density-independent. Pesticides vary greatly
in their toxicity and persistence and solubility. There are differences of
response to one chemical between species, sexes, age groups and individuals. Sublethal effects on reproduction and behaviour are likely to
be ecologically significant. Persistence and fat solubility cause organochlorine insecticides to become widely dispersed and concentrated in
food chains. Little is known about the ecological effects of pesticide
interaction (potentiation). Pesticides have been used for over 200 years
but they have only become an important ecological factor during the
past 20 years. Existing statistics are inadequate in assessing the amount
of pesticides in the environment. A pesticide may affect a species
directly by delayed effect and by affecting food species, habitat, competitors and predators. Pesticides usually reduce diversity and since
they have differential effects on taxa at different trophic levels they
may affect production. Pesticides, like all deleterious density-independent factors, are likely to have a particularly severe effect on predators.
This effect is enhanced in the case of organochlorine insecticides by the
food chain effect (see above). Pesticides are likely to affect freshwater
ecosystems more severely than terrestrial ones. Modifications of succession by pesticides are described. The natural selection of resistant strains
by pesticides can cause qualitative changes in species. Pest control and
pesticide control are both ecological factors. Some reasons for not taking
an ecological approach to pesticide problems are discussed. It is suggested
that future trends in pest control will polarize towards two types of
system, one involving complete control of very simple systems and
others involving integrated control of complex systems. The use of
pesticides is to some extent self-regulatory. Pesticides, particularly the
more selective ones, have value as tools in ecological research.
ACKNOWLEDQMENTS
I should like to thank Dr. J. P. Dempster, Dr. D. J. Jefferies, Dr. K.
Mellanby, Dr. F. Moriarty and my wife Dr. Janet Moore for valuable
criticisms of the manuscript. Discussions with my colleagues in the
Nature Conservancy's Toxic Chemicals and Wildlife Division were most
helpful in preparing this paper - I am most indebted to all members
E
'
125
X. SUMMARY
The pesticide problem is essentially ecological and an interdisciplinary
approach to it is essential. Pesticides always affect ecosystems although
they are usually applied to control single or very few pest species. Conclusions about pesticide effects on populations must generally remain
tentative owing to the lack of information on population dynamics,
feeding habits and toxicology. Most pesticides are non-specific in their
action and their effects are density-independent. Pesticides vary greatly
in their toxicity and persistence and solubility. There are differences of
response to one chemical between species, sexes, age groups and individuals. Sublethal effects on reproduction and behaviour are likely to
be ecologically significant. Persistence and fat solubility cause organochlorine insecticides to become widely dispersed and concentrated in
food chains. Little is known about the ecological effects of pesticide
interaction (potentiation). Pesticides have been used for over 200 years
but they have only become an important ecological factor during the
past 20 years. Existing statistics are inadequate in assessing the amount
of pesticides in the environment. A pesticide may affect a species
directly by delayed effect and by affecting food species, habitat, competitors and predators. Pesticides usually reduce diversity and since
they have differential effects on taxa at different trophic levels they
may affect production. Pesticides, like all deleterious density-independent factors, are likely to have a particularly severe effect on predators.
This effect is enhanced in the case of organochlorine insecticides by the
food chain effect (see above). Pesticides are likely to affect freshwater
ecosystems more severely than terrestrial ones. Modifications of succession by pesticides are described. The natural selection of resistant strains
by pesticides can cause qualitative changes in species. Pest control and
pesticide control are both ecological factors. Some reasons for not taking
an ecological approach to pesticide problems are discussed. It is suggested
that future trends in pest control will polarize towards two types of
system, one involving complete control of very simple systems and
others involving integrated control of complex systems. The use of
pesticides is to some extent self-regulatory. Pesticides, particularly the
more selective ones, have value as tools in ecological research.
ACKNOWLEDQMENTS
I should like to thank Dr. J. P. Dempster, Dr. D. J. Jefferies, Dr. K.
Mellanby, Dr. F. Moriarty and my wife Dr. Janet Moore for valuable
criticisms of the manuscript. Discussions with my colleagues in the
Nature Conservancy's Toxic Chemicals and Wildlife Division were most
helpful in preparing this paper - I am most indebted to all members
E
'