Field Comparison of Different Strains of Gypsy Moth Nuclear Polyhedrosis Virus Against Gypsy Moth (Lepidoptera: Lymantriidae) in Western Maryland in 1990

Gypchek, as the LD P226 strain of the nuclear polyhedrosis virus of the gypsy moth, Lymantria dispar (L.), was compared in small forest plots with the Abington isolate (Pass 10), each at three dosages. Also evaluated were one dose of virus produced in cell culture, one dose of Gypchek applied without sunscreen, and an untreated control. A dose-response was demonstrated for both the Abington and Gypchek strains. The Abington isolate killed significantly faster than the Gypchek strain, but no statistical difference was seen in virulence, as measured by larval mortality, between the two products. Virus produced in cell culture was found to be active in the bioassay of field-collected larvae. The presence or absence of the sunscreen Orzan did not affect results. Treatment effects as measured by late-season field parameters (larval mortality, defoliation, and egg mass population change) were obscured by forest-wide natural mortality factors.