A SYNOPSIS O F THE PESTICIDE PROBLEM
97
concentrations which were 11200 of the concentrations producing 96-hour
median tolerated limit (TLm). At higher doses changes in behaviour
could be related to a reduction in brain acetyl cholinesterase level but
at lower doses important changes could occur without demonstrable
reduction. Warner and his colleagues have shown that quantitative
measurements can be made of pesticide effects on many learned and
innate responses in aquatic anim.als, including sensitivity to light and
noise, habituation, conditioned reflexes and memory (Warner et al.,
1966).
The failure of a bird’s egg to hatch may sometimes be due to toxic
effects on the egg, but it may also be due to the effects of the pesticide
on the incubating behaviour of the adult bird (Genelly and Rudd,
1956). Many birds are known to smash and/or eat their own eggs
under stress. It has even been suggested that this is an innate population
regulatory mechanism (Wynne Edwards, 1962). Ratcliffe (1958) and
Prestt (pers. comm.) have reported on apparent increases in this habit
in the peregrine falcon and sparrow-hawk respectively. Ratcliffe (in
press) has suggested that in the case of the peregrine falcon the practice
is correlated with the use of organochlorine insecticides. If this hypothesis is correct it is an example of a pesticide affecting complex
instinctive behaviour in birds. Ogilvie and Anderson (1965) have shown
that DDT affects temperature selection by immature Atlantic salmon,
and suggested that this insecticide may interfere with the normal
acclimatization mechanism.
Selective pressure is so strong that any population whose average
learning ability is reduced or whose instinctive reactions are altered
will be likely to undergo a population change and its role in the
ecosystem may be profoundly altered.
c. PERSISTENCE A N D SOLUBILITY
Apart from its toxicity the most important characteristic of a pesticide from the ecological point of view is its stability. For most purposes
persistence is an undesirable characteristic in crop protection since
persistent compounds will leave residues on food; but against soil pests
and animal parasites some degree of persistence is essential. Stability
as observed in the field has both physico-chemical and biological
aspects. A further distinction must, be made between persistence in an
available and toxic form and harmless persistence ; herbicides of the
quaternary ammonium group (paraquat and diquat) are examples of the
latter: they are quickly inactivated on contact with the soil but remain
in the soil for many months. In this case it appears that persistence is
not hazardous (J. Newman, pers. comm.). Persistence in a toxic form
is important because it allows dispersal of toxic chemicals to places
97
concentrations which were 11200 of the concentrations producing 96-hour
median tolerated limit (TLm). At higher doses changes in behaviour
could be related to a reduction in brain acetyl cholinesterase level but
at lower doses important changes could occur without demonstrable
reduction. Warner and his colleagues have shown that quantitative
measurements can be made of pesticide effects on many learned and
innate responses in aquatic anim.als, including sensitivity to light and
noise, habituation, conditioned reflexes and memory (Warner et al.,
1966).
The failure of a bird’s egg to hatch may sometimes be due to toxic
effects on the egg, but it may also be due to the effects of the pesticide
on the incubating behaviour of the adult bird (Genelly and Rudd,
1956). Many birds are known to smash and/or eat their own eggs
under stress. It has even been suggested that this is an innate population
regulatory mechanism (Wynne Edwards, 1962). Ratcliffe (1958) and
Prestt (pers. comm.) have reported on apparent increases in this habit
in the peregrine falcon and sparrow-hawk respectively. Ratcliffe (in
press) has suggested that in the case of the peregrine falcon the practice
is correlated with the use of organochlorine insecticides. If this hypothesis is correct it is an example of a pesticide affecting complex
instinctive behaviour in birds. Ogilvie and Anderson (1965) have shown
that DDT affects temperature selection by immature Atlantic salmon,
and suggested that this insecticide may interfere with the normal
acclimatization mechanism.
Selective pressure is so strong that any population whose average
learning ability is reduced or whose instinctive reactions are altered
will be likely to undergo a population change and its role in the
ecosystem may be profoundly altered.
c. PERSISTENCE A N D SOLUBILITY
Apart from its toxicity the most important characteristic of a pesticide from the ecological point of view is its stability. For most purposes
persistence is an undesirable characteristic in crop protection since
persistent compounds will leave residues on food; but against soil pests
and animal parasites some degree of persistence is essential. Stability
as observed in the field has both physico-chemical and biological
aspects. A further distinction must, be made between persistence in an
available and toxic form and harmless persistence ; herbicides of the
quaternary ammonium group (paraquat and diquat) are examples of the
latter: they are quickly inactivated on contact with the soil but remain
in the soil for many months. In this case it appears that persistence is
not hazardous (J. Newman, pers. comm.). Persistence in a toxic form
is important because it allows dispersal of toxic chemicals to places