The role of parasitoids and virus infections in the population dynamics of mass species of insects-phyllophages

Abstract

The role of parasites (parasitoids and infections) in the population dynamics of the gypsy moth (Lymantria dispar L.) and the nun moth (Lymantria monacha L.), which are prone to large-scale and panzonal periodic outbreaks, is discussed. The results of long-term research have shown that parasites are not the key regulators of the abundance of forest phytophagous insects with high biotic potential, even though they reduce its values, mainly because of the elimination of specimens with low viability. Outbreaks of these parasites are explained by the influence of stress abiotic factors (for example, of droughts) on cenopopulations of woody plants rather than by a delay in parasitic activity or insect escape. Plant reactions to stress under certain biotopic conditions cause changes in the biochemical composition of leaves and needles that are favorable for phyllophages with high biotic potential and rapid adaptation to new environmental and climatic conditions. For this reason, in the system of tree-phytophage interactions, the trophic factor is of primary importance. This role in the phytophage-parasite system is indirectly associated with a sharp decline in the immunity of insects and their increased sensitivity to parasites. It should be noted that this assumption is significant only for forest phytophagous insects having high biotic potential, which are subjected to large-scale and panzonal periodic outbreaks of their abundance.