Exploration into a mechanism of transgenerational transmission of nucleopolyhedrovirus in Lymantria dispar L. in Western Siberia

The mechanisms of nucleopolyhedrovirus (NPV) transmission through gypsy moth (Lymantria dispar L., Lepidoptera: Lymantriidae) populations in Western Siberia were investigated. Field and laboratory studies were carried out during 1992-1998 in a gypsy moth outbreak in the Novosibirsk Area (Western Siberia), Russia. The damaged trees were primarily two species of birch, Betula pendula Roth. and B. pubescens Ehrh. Investigations were performed at three stages of the outbreak: population increase (1992-1993), population peak (1994-1995) and population decline (1996-1998). Experiments on activation of occult virus by different stress factors were carried out in order to clarify the mechanism of transgenerational transmission of NPV. In both laboratory and field experiments NPV-caused mortality levels were low; most insects did not acquire a lethal dose of virus. Occult virus can provide an important route of transgenerational NPV transmission, particularly in Western Siberia where gypsy moths migrate by female flight and can move away from trees contaminated by virus from previous larval infections.