Forest thinning affects reproduction in pine engravers (Coleoptera: Scolytidae) breeding in felled lodgepole pine trees

Reproduction in bark beetles (Coleoptera: Scolytidae) is known to be affected by abiotic factors, especially temperature, and by the quality of individual beetles. Both of these factors are affected by forest structure, yet the effects of forest structure on reproduction in bark beetles have not been widely shown in field studies. Here we investigate how changes in forest structure due to thinning of mature lodgepole pine, Pinus contorta variety latifolia Engelmann, stands affect reproduction in pine engravers, Ips pini (Say), breeding in felled trees. To do this, we excavated pine engraver gallery systems in thinned and unthinned stands at the end of the breeding season. Males in thinned stands attracted more females than in unthinned stands. Also, females in-thinned stands extended their egg galleries farther, laid more eggs, and had higher egg densities than in unthinned stands. These results are consistent with increased temperatures in thinned stands, but may also be attributable to differences in individual quality resulting from easier dispersal in thinned stands. Regardless, the observed increases in reproduction likely reflect higher reproductive success in thinned stands than in unthinned stands, and the effects of thinning on population dynamics of bark beetles should be further investigated.