Parasites of Rhyacionia buoliana and Their Occurrence at Different Crown Levels of Red Pine in Wisconsin1

Abstract

The native parasite complex associated with the introduced European pine shoot moth, Rhyacionia buoliana Schiffermüller), at Two Rivers, Wisconsin, includes 2 dipterous and 18 hymenopterous species. Data are presented on the percent parasitization effected by the parasite complex, the activity of each of the species involved, and the portion of the tree crown from which hosts parasitized by these species were collected. These data are used to define the area of crown-level activity in which host finding and subsequent parasitism occur. The commonest parasites reared were the primaries Hyssopusthymus Girault and Exeristes comstockii (Cresson), and the secondaries Eurytoma pini Bugbee and Habrocytus thyridopterigis Howard. Average parasitization from 1961 to 1963 was 8.34%. Based on the expected number of parasitized hosts per 1000 infested buds, Hyssopus thymus appears to be the most important parasite. It shows about equal preference for hosts in middle and lower crown levels. Effectiveness of Exeristes comstockii is limited because it is heavily hyperparasitized, requires an alternate host, and is a solitary form. Exeristes comstockii is most active in the middle crown. Eurytoma pini is the most active secondary parasite; it is equally active in the middle and lower crown levels.