Genetic evidence of broad spreading of Lymantria dispar in the West Siberian Plain

Abstract

Gypsy moth Lymantria dispar L. 1758 (Lepidoptera: Erebidae) is one of the most dangerous forest pests of the Holarctic region. Outbreaks of gypsy moth populations lead to significant defoliation of local forests. Within the vast territory of the West Siberian Plain, we noted the outbreak front movement in the north-east direction with a speed 100–200 km per year. The reason for the outbreak’s movement is still unclear because L . dispar females are characterised by limited flight ability, which is not enough to support that movement per se . Herein, we analysed the mtDNA divergence pattern among L . dispar populations collected from the vast territory of the West Siberian Plain to determine the boundaries of populations and reveal the effect of the outbreak’s front movement on mtDNA patterns of populations. The 590-bp region of the cytochrome oxidase subunit I gene of the mitochondrial genome was sequenced for 220 specimens that were collected from 18 localities along a transect line (~ 1400 km). Our results clearly show that the gypsy moth populations of the vast Siberian territory are not subdivided. This result can be explained by extensive genetic exchange among local populations. Taking into account that the flight ability of L . dispar females is rather limited, we suggest that spreading occurs through ballooning of early instar larvae. This hypothesis was confirmed by the coincidence of the outbreaks’ movement direction with that of the dominant winds, complemented by the observation of ballooned larvae far from a forest edge.

Persistence and genetic diversity of Lymantria dispar multiple nucleopolyhedrovirus in soil during an epizootic

“…This is possibly because either genetically different LdMNPV strains survived in other soil samples within the study site and infected the larvae or new LdMNPV strains were introduced from the outside of the study site. In forest lepidopterans, the 1st-instar larvae can move several kilometers by ballooning [44], and L. dispar larvae move up to 15 km by ballooning on strong winds [45]. Considering the fact that the larvae disperse by ballooning during the early-instar stage and by crawling on the ground after the middleinstar stage [9], new LdMNPV strains could have been introduced into the study site by LdMNPV-infected larvae that can disperse in the early stage of virus infection and survive for about a week before virus-induced death.…”

Susceptibility of the Gypsy Moth Lymantria dispar (Lepidoptera: Erebidae) to Nosema pyrausta (Microsporidia: Nosematidae)

“…The progeny of approximately 200 females were collected as egg masses from two localities in the Novosibirsk region, corresponding to the two local populations. According to our recent mtDNA data, insects from both studied localities belong to same metapopulation [ 17 ]. The locality #1 originated from Bazovo, Novosibirsk Region, Russia (54.56° N, 81.21° E) and was at the phase of the rise in population density.…”

The Asian gypsy moth (Lymantria disparL.) populations: resistance of eggs to extreme winter temperatures

“…On the contrary, an early formation of snow cover (before severe frosts), along with other factors, can provoke a GM population outbreak, because most eggs will successfully overwinter. We believe that one of the causes of the observed asynchronicity of GM population outbreaks in the Asian part of its range (Martemyanov et al, 2019) may be fluctuations of weather conditions. It is in contrast to the European part of the GM range, where the outbreaks were synchronous (Liebhold et al, 2000;Esper et al 2007;Soukhovolsky et al, 2015) and where winter temperatures are usually not below -30 °С.…”

“…Gypsy moth Lymantria dispar L. 1758 (Lepidoptera: Erebidae) is a polyphagous insect and one of the most important pests in forestry, because periodical outbreaks can cover hundreds of thousands of hectares of forest areas (Qian, 2000;Ponomarev et al, 2012). The role of various factors determining the dynamics of gypsy moth (GM) population outbreaks remains debatable (Liebhold et al, 2000;Ponomarev et al, 2012;Martemyanov et al, 2019). Another issue is related to the observed climate changes (IPCC, 2013), which are particularly pronounced in the circumpolar regions of Siberia: how will the Siberian GM populations respond to warming?…”