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A Contribution to the Study of Biological Control and Parasite Introduction in Continental Areas

Published online by Cambridge University Press:  06 April 2009

W. R. Thompson
W. R. Thompson
Affiliation:
From the European Parasite Laboratory of the U.S. Bureau of Entomology, Hyères, France.
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Extract

1. The most striking successes with the method of biological control by the introduction of the parasitic and predaceous enemies of foreign pests, appear to have been obtained mainly in island areas; some doubt exists concerning the utility of the method in continental areas.

2. Three main objections may be raised to the use of the method of parasitic introduction in continental areas. The first is based on the similarity between the faunas and floras of such continental areas as Europe and North America, the second on the polyphagous habit of many parasites, the third on the behaviour of hyperparasites in relation to introduced primaries.

3. The studies made on the natural control of indigenous species in continental areas show that control is effected by complexes of many factors differing both quantitatively and qualitatively in the different parts of the habitat.

4. This fact appears at first sight to indicate the inutility of many of the factors involved, as, for example, the parasitic enemies.

5. The answer to this difficulty is to be found principally in the fact that the quantitative and qualitative fluctuations in the composition of the controlling complexes are much less important than they appear.

6. The effect of the disappearance of controlling factors of the two main types from controlling complexes of various kinds, is studied in detail in order to make this clear.

7. The action of many factors is thus shown to be much less important than it appears at first sight. Nevertheless, this action is real and to a certain degree indispensable in a given environment. The disappearance of a factor from a system in equilibrium will thus permit the increase and spread of the host.

8. The effects which follow the introduction of foreign pests in continental areas constitute a clear demonstration of their escape from control.

9. The evidence indicates that the factor whose absence has permitted increase and spread is the parasitic factor.

10. Equilibrium can be re-established in several ways. Mechanical methods must not be neglected and will normally interfere very little with the biological method; but it is to the latter method that we must turn for a hope of permanent and inexpensive control.

11. The practical results obtained by parasite introduction in continental areas tend in general to support the ideas defended in this paper, and justify the introduction of the native parasites and predators of foreign pests even in the case of exchanges between continental areas.

Type
Research Article
Information
Parasitology , Volume 20 , Issue 1 , April 1928 , pp. 90 - 112
Copyright
Copyright © Cambridge University Press 1928

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References

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1 For some parasites which feed on their hosts and thus also act as predators, this is not absolutely true: but it is sufficiently accurate for all practical purposes.

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