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N. W. MOORE
2. Pesticides act independently of the density of the pest against
which they are used. Therefore they cannot control pests in the
manner of predators.
3. Their effect on density-dependent factors is indirect: pesticides
are likely to alter preylpredator relationships to the detriment of
the predator and hence to reduce the effectiveness of control by
predators.
4. Pesticides are likely to produce resistant strains in pests.
A perusal of the pesticide literature shows that many workers still
think of pest resurgences and resistant strains as exceptional; toxicological data are still considered adequate to predict effects in the field.
Research on biological (or integrated) control still receives relatively
little support. These facts strongly suggest that pesticides are not yet
thought of primarily in terms of population ecology. It is important
to know why this is the case. Undoubtedly one of the reasons is that
chemical manufacturers can still make adequate profits by selling
chemicals as short-term pest eradicators. But I believe that there are
methodological reasons for discounting an ecological approach. Since
they affect pesticide investigations at many points, and have wider
implications, tentative explanations are given below.
The belief that toxicological tests are adequate to predict the effects
of a pesticide in the field may be taken as an example of a non-ecological
approach to pesticides. It appears to stem from two fallacies, namely:
1. Since studies a t lower levels of enquiry (biochemistry, physiology)
are more fundamental than those at higher levels (population
ecology) they are better guides for making all predictions.
2. Explanations at one level of enquiry can be transferred to another.
Toxicological studies can only tell one the proportion of individual8
which will die if they eat given amounts of contaminated food. The
actual effect of a pesticide on a wild population will depend on the
extent to which the pesticide affects its breeding stock as opposed to
surplus individuals. A pesticide might kill 90% of the individuals, but
if these were surplus to the breeding stock it might have very little
effect on the species. On the other hand a 10% reduction of the breeding
stock might have serious consequences. Toxicological information together with information on feeding habits is important in assessing the
initial kill, but by itself can tell one little about the long-term effects
on the population. Therefore, wherever possible, predictions of the effects
of pesticides on populations should be based on field experiments. Unfortunately these are impracticable in many instances and assessments
have to be based on circumstantial evidence. The validity of circumstantial evidence is sometimes doubted: there seems to be a tendency
to put more weight on the results of laboratory experiments, even if
N. W. MOORE
2. Pesticides act independently of the density of the pest against
which they are used. Therefore they cannot control pests in the
manner of predators.
3. Their effect on density-dependent factors is indirect: pesticides
are likely to alter preylpredator relationships to the detriment of
the predator and hence to reduce the effectiveness of control by
predators.
4. Pesticides are likely to produce resistant strains in pests.
A perusal of the pesticide literature shows that many workers still
think of pest resurgences and resistant strains as exceptional; toxicological data are still considered adequate to predict effects in the field.
Research on biological (or integrated) control still receives relatively
little support. These facts strongly suggest that pesticides are not yet
thought of primarily in terms of population ecology. It is important
to know why this is the case. Undoubtedly one of the reasons is that
chemical manufacturers can still make adequate profits by selling
chemicals as short-term pest eradicators. But I believe that there are
methodological reasons for discounting an ecological approach. Since
they affect pesticide investigations at many points, and have wider
implications, tentative explanations are given below.
The belief that toxicological tests are adequate to predict the effects
of a pesticide in the field may be taken as an example of a non-ecological
approach to pesticides. It appears to stem from two fallacies, namely:
1. Since studies a t lower levels of enquiry (biochemistry, physiology)
are more fundamental than those at higher levels (population
ecology) they are better guides for making all predictions.
2. Explanations at one level of enquiry can be transferred to another.
Toxicological studies can only tell one the proportion of individual8
which will die if they eat given amounts of contaminated food. The
actual effect of a pesticide on a wild population will depend on the
extent to which the pesticide affects its breeding stock as opposed to
surplus individuals. A pesticide might kill 90% of the individuals, but
if these were surplus to the breeding stock it might have very little
effect on the species. On the other hand a 10% reduction of the breeding
stock might have serious consequences. Toxicological information together with information on feeding habits is important in assessing the
initial kill, but by itself can tell one little about the long-term effects
on the population. Therefore, wherever possible, predictions of the effects
of pesticides on populations should be based on field experiments. Unfortunately these are impracticable in many instances and assessments
have to be based on circumstantial evidence. The validity of circumstantial evidence is sometimes doubted: there seems to be a tendency
to put more weight on the results of laboratory experiments, even if