The experimental study on the occurrence of new probabletrophic links for Polygraphus proximus Blandf. (Coleoptera: Curculionidae, Scolytinae)in Western Siberia

Far Eastern species Polygraphus proximus Blandf. is the most dangerous invasivepest of fir forests, discovered in Western Siberia in 2008. This paper presents the resultsof experimental study of fir bark beetle breeding ability on the previously unrecorded ashost tree conifer species in the new habitat. The method of laboratory pests breeding onnon-colonized healthy logs, was used in this investigation. The logs of Siberian stonepine Pinus sibirica Du Tour, Siberian spruce Picea obovata Ledeb. and Siberian larchLarix sibirica Ledeb., collected from windfall. The beetles which used for colonizationwere obtained from naturally infested Siberian fir. For the control infestation of Siberianfir logs were used the beetles belonged to the second generation came from laboratorybreeding on the three species. The experiment lasted 110 days. Intensive boring wasobserved at 3-4 day, primarily with the end surfaces. On the surface of three speciestested, there is a thick bark, which probably can prevent males to push out the fecalpellets from nuptial chamber. Part of parental generation beetles moved out for thecreating new families at the 17-20 day. The active emergence of first beetles generationbegan at the 55-th day, and second generation of fir bark beetles appeared in 110 day.At the end of the observations the bark of infested logs was removed, and demographiccharacteristics of P. proximus were determined. At the fir logs that have been set later,there were found many young adults. The estimated demographic characteristicsobtained in lab on A. sibirica consistent with those observed in nature. Beetles thathave emerged before the setting of fir, continued development of free sites on Siberianstone pine, larch and spruce logs, from which they had moved out. Experimental dataconfirm the probability of occurrence of the second generation under Western Siberiaconditions.The data obtained in the laboratory, indicate a high offspring production ofP. proximus. The number of offspring produced on fir log exceed the parental generationat 6.97 times. At the same time on other conifers, according to the gradations ofperformance assessment of stem pests reproduction, high energy of breeding polygraphshowed during developing on Siberian larch (4.98) and on Siberian spruce (3.21)and also average (1.98) on Siberian stone pine. The laboratory tests confirmed theassumption of able the fir bark beetle developing on the Pinus sibirica Du Tour, Piceaobovata Ledeb., Larix sibirica Ledeb. and give fertile offspring, feeding on them. Thecomparison of demographics P. proximus, under experimental conditions showed thatafter the fir - the main host tree in Western Siberia, most favorable for the development -is a larch, and the least favorable - Siberian stone pine.

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