Height Distribution of Adult Parasitoids of the Southern Pine Beetle Complex

Abstract

The height distribution of adult parasitoids of the Dendroctonus frontalis Zimmermann complex trapped on the boles of Pinus taeda L. trees was examined. The study was conducted within two active D. frontalis infestations in the Talladega National Forest in Alabama in July 1998. Stickem Special-coated 15 × 20 cm wire mesh (6 mm2) traps were placed on pines with late instar to adult D. frontalis and Ips spp. at 2 m intervals to a height of 16 m on 12 trees and at 4-m intervals to a height of 16 m on 6 trees. Traps were changed on alternate days for 14 d, and all adult parasitoids of the D. frontalis complex were identified and counted. There was a positive correlation between height and number of parasitoids. This is most likely due to the high proportion of Roptrocerus xylophagorum Ratzeburg and Heydenia unica Cook and Davis collected, because both of these species preferred the upper bole. Each parasitoid species had different height distributions. R. xylophagorum, H. unica and Dendrosoter sulcatus Muesebeck all preferred the upper bole, with a peak trap catch between 12 and 16 m. In contrast, Coeloides pissodis (Ashmead) and Dinotiscus dendroctoni (Ashmead) both preferred the midbole, with a peak catch at 6 m. Only Spathius pallidus Ashmead showed no height preference; however, this species also had the lowest trap catch. Although each parasitoid species had its height preferences, all species were distributed throughout the length of the infested bole.