Spatial Distribution of Overwintering Eggs of the White Apple Leafhopper, Typhlocyba pomaria , and Parasitism by Anagras epos1

Abstract

Overwintering eggs of the white apple leafhopper (WALH), Typhlocyba pomaria McAtee, parasitized and unparasitized by the mymarid, Anagrus epos Girault, were randomly collected from apple twigs taken from within quadrants and levels of apple trees in 3 Michigan orchards. Subsamples included host eggs from twig bark of different age classes and at varying distances from the apex of the branch terminal. WALH eggs were most common on twig wood 3–4 yr old or 45–75 cm from the apex. In 2 of 3 orchards more dense populations were found in the upper tree canopy as compared to the lower. From ANOVA, variations in WALH densities more often were significantly different between trees (P ≦ 0.01 level) as compared to within trees in different quadrants and levels. The distribution of eggs parasitized by A. epos within trees and between trees was very similar to the distribution of the WALH, indicating that parasite search was well adapted to the ovipositional site preference of the host. Analysis of percent parasitization of WALH eggs per tree indicated a density dependent association between these 2 species in an orchard having the highest WALH density.