New Outbreak of Dendrolimus sibiricus Tschetv. in Siberia (2012–2017): Monitoring, Modeling and Biological Control

Abstract

The territory of the new mass outbreak of Dendrolimus sibiricius is northernmost Siberia. The present increase in the pest numbers started in 2011–2012, 14 years after the previous mass outbreak. As a result, the area of damage to dark coniferous forests exceeded 1.4 million ha. The reasons for the emergence of the pest population from a depressive state are insufficient moisture availability in May 2011, severe droughts in June–July 2012, and increased mean monthly temperature. A significant decrease in the vegetation index of SWVI occurred in 2011–2012. The hydrothermal regime of the spring–summer period in these years promoted the transition of most of the pest populations to development over 1-year generation. One exceptional feature of the current outbreak is low damage to D. sibiricus caterpillars by diseases and parasites. Favorable weather conditions and a low number of natural entomopathogens contribute to the rapid spread of the pest in northern and eastern directions. This creates a high risk of mass outbreak of D. sibiricus in dark coniferous forests, since the area of nearby dark coniferous stands suitable in structure, climatic, and forest-growing conditions for the pest dispersal is more than 2.7 million ha. Pure cultures of the entomopathogenic fungus Beauveria bassiana were isolated from dead caterpillars of D. sibiricus. Multistage screening made it possible to select a promising strain for the creation of a long-acting bioinsecticide for the preventive treatment of forests. The main selection criteria are high virulence, high entomopathogenic activity at low temperatures (7–10°C), and the ability for solid-phase fermentation of plant waste.