96
N. W. MOORE
DDT is concentrated in the spermatozoa as well as in the eggs of
oysters (Butler, 1966). DDT is known to affect sperm production in
the fowl (Albert, 1962). The relative importance to the offspring of the
contamination of male and female gametes is not known. In mammals
the young animal can receive pesticide residues from its mother's milk
(Laug et al., 1951).
Insect pests have been controlled by the release of male flies previously sterilized by radiation or by chemicals. For a review on chemosterilants see Bushland (1960). The use of chemosterilants is not
extensive. If it were to become so it could have serious ecological
consequences.
The potential importance of altering expectation of life is obviously
great. It is generally accepted that the number of young produced by
any species is an adaptation resulting from natural selection. Therefore,
any factor which alters the number which in fact survive is likely to
have an important effect, though the actual effect in any one instance
will depend on the particular circumstances of the breeding season in
question. In one particular season a reduction in the average number
of young produced might not be harmful, for example if food supply
were unusually low and inadequate to feed the young. Toxicological
work can show whether changes in breeding success are likely to result
from specific uses of a pesticide, but it cannot show whether the effects
will cause important changes in the population concerned.
Pesticides can affect growth; for example, Butler (1966) reports that
concentrations of 0.001 ppm of DDT cause a marked reduction in the
rate of oyster shell growth.
(ii) Behawiour. The only other type of sublethal effect which has been
studied intensively is the effect on behaviour. Increased activity, tremoring and lack of coordination are well-known symptoms of organochlorine insecticide poisoning in many animals. Dieldrin causes the fox
and other animals to seek water. These symptoms develop in animals
which are likely to die in any case. They are ecologically important in
prey species since abnormal movements make them more conspicuous
and therefore they are more likely to be taken by predators than are
animals not showing the symptoms. Too little is known about the effects
of low doses of pesticides on behaviour to say whether they cause
population changes; published work, however, is suggestive. Warner
et al. (1966) (see also Ludwig, 1965) working on fish have shown that
both organophosphorus and organochlorine insecticides can affect the
learning ability of these organisms. They demonstrated that extremely
'low concentrations (0.4 pg/l of toxaphene applied for 11 days and
21 pg/l of TEPP applied for 4 days) resulted in alterations in behaviour. Behavioural pathological symptoms were produced by TEPP
N. W. MOORE
DDT is concentrated in the spermatozoa as well as in the eggs of
oysters (Butler, 1966). DDT is known to affect sperm production in
the fowl (Albert, 1962). The relative importance to the offspring of the
contamination of male and female gametes is not known. In mammals
the young animal can receive pesticide residues from its mother's milk
(Laug et al., 1951).
Insect pests have been controlled by the release of male flies previously sterilized by radiation or by chemicals. For a review on chemosterilants see Bushland (1960). The use of chemosterilants is not
extensive. If it were to become so it could have serious ecological
consequences.
The potential importance of altering expectation of life is obviously
great. It is generally accepted that the number of young produced by
any species is an adaptation resulting from natural selection. Therefore,
any factor which alters the number which in fact survive is likely to
have an important effect, though the actual effect in any one instance
will depend on the particular circumstances of the breeding season in
question. In one particular season a reduction in the average number
of young produced might not be harmful, for example if food supply
were unusually low and inadequate to feed the young. Toxicological
work can show whether changes in breeding success are likely to result
from specific uses of a pesticide, but it cannot show whether the effects
will cause important changes in the population concerned.
Pesticides can affect growth; for example, Butler (1966) reports that
concentrations of 0.001 ppm of DDT cause a marked reduction in the
rate of oyster shell growth.
(ii) Behawiour. The only other type of sublethal effect which has been
studied intensively is the effect on behaviour. Increased activity, tremoring and lack of coordination are well-known symptoms of organochlorine insecticide poisoning in many animals. Dieldrin causes the fox
and other animals to seek water. These symptoms develop in animals
which are likely to die in any case. They are ecologically important in
prey species since abnormal movements make them more conspicuous
and therefore they are more likely to be taken by predators than are
animals not showing the symptoms. Too little is known about the effects
of low doses of pesticides on behaviour to say whether they cause
population changes; published work, however, is suggestive. Warner
et al. (1966) (see also Ludwig, 1965) working on fish have shown that
both organophosphorus and organochlorine insecticides can affect the
learning ability of these organisms. They demonstrated that extremely
'low concentrations (0.4 pg/l of toxaphene applied for 11 days and
21 pg/l of TEPP applied for 4 days) resulted in alterations in behaviour. Behavioural pathological symptoms were produced by TEPP