The influence of silhouette color and orientation on arrival and emergence of Ips pine engravers and their predators in loblolly pine

Abstract

Insects that rely upon aggressive bark beetles (Coleoptera: Scolytidae) for generating appropriate habitats (natural enemies and associated species) must respond to a variety of stimuli used by bark beetles, including semiochemical and visual cues. In the southeastern US, Ips engraver beetles are non-aggressive bark beetles that exploit both standing and downed trees (vertically and horizontally oriented targets). The objective of this experiment was to evaluate whether changes in visual silhouettes (color and orientation) affected the colonization patterns of Ips engravers and their natural predators in loblolly pine logs. We found that the total number of Ips arriving at loblolly pine logs was significantly affected by color. About 48% fewer Ips were caught at logs painted white than those painted black, and 32% fewer than at unpainted. Of the predators arriving in sufficient numbers to evaluate, Medetera bistriata parent (Diptera: Dolichopodidae) and Platysoma spp. (Coleoptera: Histeridae) were significantly affected by color, with white logs catching fewer numbers in each case. Orientation of host logs (horizontal and vertical) affected both M. bistriata and Lonchea spp. (Diptera: Lonchaeidae) but not Ips. Lonchea were significantly and consistently more attracted to horizontal logs. M. bistriata, on the other hand, were inconsistently more attracted to vertical logs, i.e., the interaction between season and orientation was as strong as the main effect for orientation. Thanasimus dubius (F) (Coleoptera: Cleridae) and anthocorid bugs were not caught in sufficient numbers for valid analysis. Overall, these results are similar to those obtained by funnel trapping, suggesting that visual responses are robust across different environmental conditions. Further, our results suggest that color treatments could be used to manipulate behaviors of predators and prey somewhat independently. This may be important for research, to evaluate relationships at a range of densities, and management, to develop treatments that reduce losses of natural enemies when bark beetles are targeted.