Abstract
In May 1988, inoculative releases (≈6,000 adults per site) of a Japanese strain of the encyrtid Holcothorax testaceipes (Ratzeburg) were made in the center of two unsprayed and two sprayed Connecticut apple orchards infested by Phyllonorycter spp. The encyrtid became established only at unsprayed sites, killing between 1 and 35% of parasitized larvae of Phyllonorycter blancardella (F.) in generations examined between 1988 and 1991. The proportion of parasitized larvae killed by H. testaceipes was higher in the first and third generation than in the second generation, which was a pattern sometimes observed in the endoparasitic Pholetesor omigis (Weed). The relative amount of mortality caused by H. testaceipes differed between unsprayed sites. In all orchards, the braconid P. omigis or the eulophid Sympiesis marylandensis Girault tended to dominate parasitoid guilds both before and after the release. The total amount of parasitism was higher at unsprayed than at sprayed sites, and parasitism by H. testaceipes was higher in the first than in the second generation. The amount of parasitism by the encyrtid was distributed uniformly throughout orchards in four of six (66.7%)generational samples. After the first generation of 1988, the mean distance of progeny from the tree where adults initially were released was similar in each generation within an orchard. In unsprayed orchards, the density in the generation of the release was 1.0-1.7 mines per 100 leaves, and density never exceeded 6.1 mines per 100 leaves thereafter. Persistence at low mine densities, oviposition in leafminer eggs, and rapid dispersal after release are desirable attributes of H. testaceipes , but itswidespread establishment in commercial orchards will depend on modifying current chemical control programs or releasing a resistant strain.
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