The dependence of the morphological and physiological indices of Lymantria dispar (L.) (Lepidoptera: Lymantriidae) postembryonic stages from temperature conditions during embryogenesis

In the light of global climatic changes the urgency of refining the adaptive mechanisms of insect survival in the northern part of their range increases. Gypsy Moth Lymantria dispar (L.) is considered to be a spring-summer phyllophagous-insect species. Individuals of this species overwinter in the embryonic stage inside the eggshells. It is classically considered that summer-autumn development of the gypsy moth embryo requires about 300 grade days with a threshold above 7°С. The summer-autumn sum of effective temperatures (SET) that is received by embryos may significantly vary both with weather conditions of summer season and for different populations or inside the range of one population. The aim of this work was to determine the possible effect of this factor on development indices of gypsy moth larvae and to analyze the possible causes in case of such effect. In this work we used egg masses from the Trans-Ural and the Lower-Volga populations of gypsy moth.We collected clutches of the Trans-Urals population in Sverdlovsk oblast in birch plantations (56°28'16'N, 61°36'39"E) in late July 2011. Clutches of the Lower Volga population were collected in Volgograd oblast in poplar plantations of the Volga-Akhtuba floodplain near Repino village (48°33'22"N, 44°47'43"E) in early August 2012 and in early July 2013. The collected egg masses were divided into two variants for getting different sums of summer-autumn effective temperatures at +24°С, following which egg masses were placed in refrigerator at 0...+2°С for passing through the cold reactivation of diapause. After diapause completion we carried out laboratory rearing of larvae from these egg masses in climatic chambers at +24°С and humidity of 60% with using artificial diet for rearing. Under natural conditions we assessed the seasonal distribution of gypsy moth male flight in 2010-2013 using pheromone-baited milk-carton traps with dispensers that contained 500 mkg (+)-dusparlure (produced in the USA). For calculation of the sum of effective temperatures of natural populations' development we used weather stations' data of daily average temperatures in Yekaterinburg and in Volgograd. The biometric methods with using elementary descriptive statistics in the StatSoft STATISTICA 6.0 software package were used for statistical processing of collected data. We analyzed the effect of the sum of summer-autumn effective temperatures, received at gypsy moth embryonic stage of development, on larvae development duration after overwintering, depending on latitudinal origination of population (northern border of the area - the Trans-Ural population and the central part of the area - the Lower-Volga population). We showed that the lowest sum of summer-autumn temperatures had the most significant influence on gypsy moth development in the northern population. We suggested that a significant response of larvae of the Trans-Ural population to the decreasing of the sum of summer-autumn effective temperatures can exist due to the fact that it is highly probable that embryos receive the sum of summer-autumn effective temperatures which are not sufficient to complete the development on the northern border of gypsy moth area that can result in extinction and subsequent area reduction. From these positions we analyzed the results of a six-year monitoring of gypsy moth flight period on the northern border of the area - the Trans-Ural population, urban and rural micropopulations of Yekaterinburg, and laboratory rearing of larvae from these micropopulations. We concluded that findings do not contradict the previously stated assumption.

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