A SYNOPSIS OF THE PESTICIDE PROBLEM
117
other characteristics. These may be advantageous (but are more
likely to be disadvantageous).
At the present time it is quite impossible to predict what evolutionary
changes will take place as a result of pesticide pressures. In some cases
resistance to pesticides is linked with other favourable characters. But
in general when pesticide pressure is withdrawn the new genotypes do
not survive; in other words those selected by pesticides are less well
adapted in general than the original type. All that can be said is that a
powerful new type of selective factor is in operation throughout the
world and it might eventually have important qualitative effects.
In the course of evolution it has always been disadvantageous to
feed on some types of potential food -those that contain poisons and
those that transmit disease to the animal. The avoidance of toxic forms
is acquired instinctively or by learning. There is often a relationship of
reciprocal advantage between prey and predator (aposematic coloration). However, there is no evidence that any species has learnt to avoid
individuals which carry disease organisms, while preying on other individuals of the same species which do not carry such organisms. In
this respect animals which contain persistent pesticides are like those
that carry diseases - it is to the advantage of the predator to be able
to distinguish the prey with the pesticide residues and the prey without,
but there is no evidence that such discrimination has yet been evolved.
Far from avoiding animals showing sublethal effects of pesticides,
predators are more likely to prey upon them as they are upon all weak
and diseased individuals. A behaviour mechanism which caused the
animal to avoid contaminated prey would have to overcome an instinct
which under “normal” conditions is effective in preventing starvation.
It is unlikely to be evolved in the present pesticide situation.
VIII. APPLICATION OF AN ECOLOQICAL APPROACH TO PESTICIDES
Today, man is a key species in most terrestrial ecosystems. In the
preceding sections pesticides have been considered as a general type of
ecological factor equivalent to fire or disease. In this section the effects
are related to the human causes which determine their use. The extent
to which any pesticide is used and the manner in which it is used
depend on two types of human activity - pest control and control of
pesticides. Both are based on scientific research and attitudes about
the effectiveness and safety of pesticides, and so it is legitimate to
consider these also as “ecological factors” in a general sense.
The conclusions from the study of pesticide effects which are most
relevant to pest control are these:
1. Pest control problems are essentially about population ecology.
A. CONTROL O F PESTS AND PESTICIDES
E
117
other characteristics. These may be advantageous (but are more
likely to be disadvantageous).
At the present time it is quite impossible to predict what evolutionary
changes will take place as a result of pesticide pressures. In some cases
resistance to pesticides is linked with other favourable characters. But
in general when pesticide pressure is withdrawn the new genotypes do
not survive; in other words those selected by pesticides are less well
adapted in general than the original type. All that can be said is that a
powerful new type of selective factor is in operation throughout the
world and it might eventually have important qualitative effects.
In the course of evolution it has always been disadvantageous to
feed on some types of potential food -those that contain poisons and
those that transmit disease to the animal. The avoidance of toxic forms
is acquired instinctively or by learning. There is often a relationship of
reciprocal advantage between prey and predator (aposematic coloration). However, there is no evidence that any species has learnt to avoid
individuals which carry disease organisms, while preying on other individuals of the same species which do not carry such organisms. In
this respect animals which contain persistent pesticides are like those
that carry diseases - it is to the advantage of the predator to be able
to distinguish the prey with the pesticide residues and the prey without,
but there is no evidence that such discrimination has yet been evolved.
Far from avoiding animals showing sublethal effects of pesticides,
predators are more likely to prey upon them as they are upon all weak
and diseased individuals. A behaviour mechanism which caused the
animal to avoid contaminated prey would have to overcome an instinct
which under “normal” conditions is effective in preventing starvation.
It is unlikely to be evolved in the present pesticide situation.
VIII. APPLICATION OF AN ECOLOQICAL APPROACH TO PESTICIDES
Today, man is a key species in most terrestrial ecosystems. In the
preceding sections pesticides have been considered as a general type of
ecological factor equivalent to fire or disease. In this section the effects
are related to the human causes which determine their use. The extent
to which any pesticide is used and the manner in which it is used
depend on two types of human activity - pest control and control of
pesticides. Both are based on scientific research and attitudes about
the effectiveness and safety of pesticides, and so it is legitimate to
consider these also as “ecological factors” in a general sense.
The conclusions from the study of pesticide effects which are most
relevant to pest control are these:
1. Pest control problems are essentially about population ecology.
A. CONTROL O F PESTS AND PESTICIDES
E