Parasitism of the Apple Blotch Leafminer, Phyllonorycter crataegella , 1 on Sprayed and Unsprayed Apple Trees in Connecticut

Abstract

Parasitism of the apple blotch leafminer, Phyllonorycter crataegella (Clemens), was investigated over nine generations (3 years) at two sites in Connecticut. Twelve species of parasitoids, three of them recorded for the first time, attacked P. crataegella immatures, their primary parasitoids, or both in commercial apple orchards. Eulophid Sympiesis marylandensis Girault, a primary ectoparasitoid, dominated in 14/16 (87.5%) of samples reared from different areas or generations. Emergence of S. marylandensis and P. crataegella adults was synchronous; however, that of S. marylandensis preceded the appearance of hosts, 4th- and 5th-instar larvae of P. crataegella , by ca. one month. Number of species and abundance of adult parasitoids varied considerably between leafminer generations, although they usually rose sharply from second to third generation in sprayed orchards. In 1978 and 1979 percent parasitism was lowest in the second and highest in the third (last) generation during each year. In the third generation of 1977 and 1979, percent parasitism was higher at the edge than at the center of commercial orchards. Percent parasitism was higher on unsprayed than sprayed trees at Southington during the first generation of 1978–1980 and during the second generation of 1978–1979. Overall percent parasitism may have been influenced negatively by insecticides and positively by immigration of parasitoids and increased developmental period of hosts (i.e., longer exposure to parasitoids).