Influence of the Density Dynamics Phase and External Conditions on the Manifestation of the Group Effect in Gypsy Moth Lymantria dispar (L.)

Based on the long-term laboratory rearing of gypsy moth larvae on an artificial diet with different modifications, which were taken from egg masses in the same forest area in different phases of the population dynamics, we have studied the effect of biotic and abiotic factors on the duration of the development and survival rate of larvae at younger instars in the group- and solitary-rearing regimes. It is shown that the duration of larval development at younger instars is influenced by the sum of effective temperatures at the early embryonic stage of development, as well as by the duration of embryo exposure to temperatures below the developmental threshold and by the food composition. The effect of the group rearing regime (group effect) on the rate of larval development is associated with the population dynamics phase; its most significant positive effect has been recorded in the eruptive period. It has been revealed that the response of larvae to the food composition through the development duration differs in different rearing regimes, depending on the population density phase. With respect to the food composition, the group effect can be determined both by the acceleration of larval development in the group regime and by the deceleration of larval development in the solitary rearing regime. The studied effects have been quantitatively assessed.