Orchard Studies on the Effect of Organic Insecticides on Parasitism of the Oriental Fruit Moth

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Abstract
Studies on the effect of organic insecticides on parasitism of the oriental fruit moth (Grapholitha molesta (Busck)) were made from 1948 through 1953 in peach orchards near Moorestown, N. J. In orchards not receiving such insecticides parasitism of twig-infesting larvae of the first two generations was as high as it was before they came into general use. It was highest in the orchard groups where there was no exposure and lowest in those having a heavy exposure to these insecticides. Significant reductions in parasite levels did not always follow heavy exposure to these insecticides, and after spray applications were discontinued for the season, both moth and parasite populations usually regained normal levels within a few weeks. The average reduction in parasitism, even in orchards heavily exposed, was usually less than 50%. Only the sprays applied before July 10 directly affected parasitism of the twig-infesting larvae. These included the early sprays used on peach, such as BHC, DDT, and the phosphorus insecticides used for control of the plum curculio or the oriental fruit moth, and similar sprays used on adjoining crops and orchards. There were instances in individual orchards of greatly reduced parasitism following moderate to heavy exposure to each of them.

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