Cascade form of process at arising of an aggressive biotype of the winter pine shoot moth (Rhyacionia buolianaschiff.)

Abstract

It has been considered the forming process of an aggressive biotype in the winter pine shoot moth. It consists of a number of consecutive in time the mechanisms and types of natural selection. The process is conditioned by existance in this region two species of pines (Pinus silvestris L. and Pinus pallasiana Lamb.) that have different level of resistance and are characterized by wide range of variability. The initial cause of the formative process was high density of the winter pine shoot moth in the stands of P. silvestris L. It stimulated growth of the aggressiveness and formation of initial aggressive group in the pest population. This group was initial one for gradual adaptation on P. silvestris L. and then on susceptible trees of P. pallasiana. The aggressive group which had been developing had a distinction by flight period in comparison with the normal population. This change served as a cause of its reproductive isolation from the normal population and led to the process of divergence. In so doing, the stabilized, directioned and disruptive types of natural selection acted step by step on different stages on the formative process.