Distribution and population characteristics of the four-eyed fir bark beetle Polygraphus proximus in the north of the Tomsk Oblast

Abstract

Studies of Polygraphus proximus Blandf. (Coleoptera, Curculionidae: Scolytinae), the invasive pest of Siberian fir, conducted in 2013-2019 in the middle taiga forests of Kolpashevsky, Verkhneketsky, Parabelsky, Kargasoksky districts of the Tomsk Oblast. The alien bark beetle was found on the territory with geographical coordinates 58°20΄02″– 59°00΄24″ N, 80°39΄21″–84°44΄40″ E in the stands of different composition, age and health condition. P. proximus colonized fir in a complex with aboriginal species of stem insects, longhorn beetle Monochamus urussovi, bark beetle Xylechinus pilosus and Buprestidae. Very rarely it infested trees independently, using mainly thin-dimensional weakened trees, sometimes large undergrowth. The number of trees infested by P. proximus in stands is small, which is explained by its relatively recent penetration into the northern regions and the lack of favorable feeding and temperature conditions for reproduction. The population density of parent generation on most model trees was characterized by low (0.19–2.9 families/dm2) and average (3.2–5.0 families/dm2) values, and only on some trees reached high values (5.3–7.4 families/dm2).The number of the daughter generation on different trees varied from low (1.9–14.8 individuals/dm2) to medium (20.3–29.8 individuals/dm2) and high (34.3–64.9 individuals/dm2). The energy of reproduction ranges from low (0.9) to medium (1.3–2.9) and high (4.7– 22.9). The range of variability of P. proximus population indicators could be due to both different intensity of interspecific relationships with aboriginal stem dendrophages, and the weakening of intraspecific competition and the press of natural enemies during a low population density of invader.