Host selection by hymenopterous parasites of the moth Plutella maculipennis curtis

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Abstract
Criticism of the procedure of earlier exponents of biological control in introducing all primary parasites and predators of a given pest, has usually stressed the harm which might result from directly competing species. It has been suggested that a more cautious approach should be made in the form of introduction of the predacious species singly, later additions to follow if observation indicates the necessity (Thompson 1930; Sweetman 1936). While this method may be prudent, the usually slow nature of biological control work results in its rejection for financial reasons. There is, perhaps, some justification for this attitude, when one recalls instances such as that of the Hessian fly parasite, Pleurotropis metallicus , which, although introduced from England into the U. S. A. In 1894, was not recovered until twenty-one years later. It has since become one of the dominant parasites of this host in the eastern states. The thesis of selection from a group of primary parasites of a given host pest has been stressed by various authors, particularly Taylor (1937) and the Hawaiian workers, Pemberton, Willard and Bissell (1918, etc.). The theory has been criticized by H. S. Smith (1929) on the ground that slight multiparasitism and competition are more than counterbalanced by the diverse ecological requirements of several different species of parasites. Smith’s criticism would appear to be borne out by later results in the Hawaiian fruit fly investigations of Willard and Mason (1937). This latter paper reviews the work from 1914 to 1933 and does not repeat the claim of earlier papers that it was a mistake to introduce some of the Opiine species.

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