Influence of Biotic and Abiotic Factors on the Duration of Development of the Spongy Moth Lymantria dispar (L.) (Lepidoptera: Erebidae) in the West Siberian Population of Different Latitudinal Origin

The study of the effect of biotic and abiotic factors on the duration of development of the spongy moth (Lymantria dispar (L.)) and the establishment of thresholds for the development of stages in individuals of the West Siberian population of different latitudinal origins (56°33′ N, 76°37′ E) (northern part of the range) and (53°44′ N, 78°02′ E) (central part of the range) has been carried out. We analyze possible ways to accelerate the development of individuals of this species in the northern part of the range: reducing the number of instars, increasing the developmental rate of instars without reducing their number, and lowering the development thresholds. It is found that the reduction in the number of larval instars is not a significant factor of the analyzed effect in this population. The threshold of late embryonic development in the West Siberian population is significantly lower than that defined for populations of the European part of Russia, and a lower threshold for the development of individuals in the northern part of the population with a low sum of effective temperatures (SET) of early embryonic development is noted. The SET of early embryonic development has a significant impact on the acceleration of the development of active stages on the northern border of the area, and the smaller it is, the higher the impact. The high plasticity of the adaptation of the species to temperature conditions allows the spongy moth to become established in new, more northern regions. This plasticity is provided both by natural selection and the reduction in threshold temperatures of development and by epigenetic mechanisms that allow adjusting the rate of development depending on the temperature conditions of the habitat.