A New Outbreak of the European Spruce Bark Beetle, Ips typographus (L.) (Coleoptera, Curculionidae) in Leningrad Province

摘要

Abstract A new and potentially severe outbreak of the European spruce bark beetle Ips typographus began in Leningrad Province in 2021. The permanent presence of the species in considerable numbers in the spruce forests of the Karelian Isthmus has created a basis for a rapid increase of its abundance. The outbreak was provoked by sharply elevated temperatures in June–July 2021, which allowed two sister and two main generations to develop successfully. Mass appearance of two generations of I. typographus was recorded for the first time for spruce forests of the Karelian Isthmus. A part of the population developed by the bivoltine type: approximately 56% of the young adults produced the second generation that successfully completed development, and others diapaused. This feature of development ensures resistance of I. typographus populations to adverse weather conditions. The part of the second generation that started to develop earlier had a high value of reproductive energy (the offspring to parent ratio): 4.7, close to that of the first generation (6.0). The next group of the second generation was apparently mainly represented by the offspring of the sister generation. The development parameters in this group were significantly lower (reproductive energy 1.3), since many of its individuals failed to complete development and prepare to diapause before the onset of cold weather in autumn. The pest stock facilitating a rapid population increase under the conditions of the Karelian Isthmus can be estimated at 140–150 thousand ind./ha, or 10–12 infested spruce trees per 1 ha. In the case reported herein, the pest stock was greater, 187 thousand ind./ha; this led to the amount of offspring reaching 3 million ind./ha, i.e., a very high density resulting in a rapidly growing outbreak. The rapid and steady growth of temperature, the presence of extensive food supply for the European spruce bark beetle in Leningrad Province and southwestern Karelia, and preservation of the pest stock suggest that this outbreak will develop rapidly and will be repeated in the near future.