Effect of Starvation as a Population Stress-Factor on the Activation of Covert Baculovirus Infection in the Gypsy Moth

Abstract

The conditions of entomopathogen persistence in a host-insect organism and the mechanisms of their conversion to the acute form of infection is one of the most important questions for an understanding of epizootics functioning. Here, we estimate the dynamics of the physiological parameters of the gypsy moth (Lymantria dispar L.) responsible for insect protection from antivirals under stress (starvation) and their correlation with the activation of the latent form of L. dispar, multiple nucleopolyhedrosis. We find that starvation leads to an increase in the dopamine concentration in the larval hemolymph and a decrease in the total number of hemocytes, which is associated with the high necrotic cell death. The number of viral carriers in the studied population and their activation level with starvation are estimated to be more than 70%. Polymerase chain reaction analysis showed an increase in the number of virus-positive individuals starting from the first day of starvation. At the same time, the nonspecific mortality of insects began only after 7 days of starvation, whereas the mortality from an activated virus began after 2–3 days of starvation. Thus, we show that at high insect-population density, a lack of food resources plays the leading role in the activation of the covert form of baculovirus infection. When analyzing the dynamics of physiological parameters, we assume that the conversion of a covert baculovirus form into an acute infection can be triggered by necrotic processes induced by starvation.