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On the Part played by Parasites in the Control of Insects living in protected Situations (1)

Published online by Cambridge University Press:  10 July 2009

W. R. Thompson
W. R. Thompson
Affiliation:
Imperial Bureau of Entomology.
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Extract

Among the injurious insects with which the entomologist attempting to utilise the methods of biological control has to deal, there are many which live in such a way that a considerable proportion of their population is practically inaccessible to parasites and predators, even during the stages when they are attractive to their enemies. Insects of this type are not infrequently transported in their animal or vegetable food materials into other territories, escape attention during the process of inspection, and develop in their new homes into devastating pests. The Mediterranean Fruit Fly, the Codling Moth, and the European Corn Borer are familiar examples of this class of pest.

Type
Original Articles
Information
Bulletin of Entomological Research , Volume 20 , Issue 4 , December 1929 , pp. 457 - 462
Copyright
Copyright © Cambridge University Press 1929

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References

* If two parasites acting in succession, attack exactly the same group of individuals and the second species is present in such numbers and so widely distributed that it is capable alone, of killing all the hosts in the group mentioned, then the action of the first species would be super-fluous, or, to put it more exactly, neither of the parasites, considered separately, would be indispensable as causes of destruction in relation to the individuals which either is capable of killing, so long as both are present. In this case, the first species might disappear without any change resulting. Thus, suppose that a certain insect is attacked in the egg stage by a Chalcid, and that the particular eggs attractive to the Chalcid, all develop into larvae attractive to an Ichneumonid, which is capable of killing all the individuals of this type including those which would be killed by the Chalcid if it were present. In such a case, the work of the Chalcid would be valueless. This seems to be the only case in which a parasite can definitely be considered as useless. For obvious reasons, such cases are not likely to occur very often.