Assessing the Flight Potential of the Four-Eyed Fir Bark Beetle Polygraphus proximus Blandford in Natural Conditions

Abstract

The four-eyed fir bark beetle Polygraphus proximus Blandford (Coleoptera, Curculionidae, Scolytinae) has become an aggressive invader in Siberia’s fir forests in recent decades. However, its spread in the invaded area is not yet complete; this species is absent so far in most of the Siberian fir Abies sibirica Ledeb. range. To predict this process, appropriate models are needed, including at the local level. One of the essential parameters for modeling is the flight characteristics of imago. To evaluate its flight potential, we placed slabs (sections of the bark with a thin sapwood layer) in an area without forests or with forests with an absence of fir at the end of May. The beetles overwintered under the bark in these slabs. We also placed short fir trap logs at distances ranging from 50 to 1500 m in the four cardinal directions from the release point to attract migrating beetles. After the beetles from the slabs had completed their migration, we evaluated the number of parental pairs (male and female) of the four-eyed fir bark beetle on the trap logs (p) and their number per dm2 (pS). The sole factor that affected the colonization of host objects in our experiment was the distance from the release point. The relationship between p and pS and the distance to the release point can be accurately represented by a negative exponential curve. This experiment established a flight distance of 1500 m, with calculated values of 4919 m for p and 2965 m for pS. However, an analysis of similar experiments and studies using flight mills suggests that these values may not be extreme in an environment with few and sparse host objects. In conditions of abundant food supply, the actual flight distance of P. proximus beetles is significantly less than the theoretically possible maximum.