SPATIAL AND TEMPORAL PATTERNS OF EMERGENCE FOR WITHIN-TREE POPULATIONS OF DENDROCTONUS FRONTALIS (COLEOPTERA: SCOLYTIDAE)

Abstract

AbstractSpatial and temporal patterns of Dendroctonus frontalis emerging from loblolly pine, Pinus taeda, were studied. Daily emergence was measured at 1.5-m intervals along the infested bole on nine trees Emerging beetles from three of the trees were collected and their sex identified. Topological estimates of daily emergence on all trees were computed and the spatial and temporal patterns of emergence were described using three and five parameter models. Emergence followed the same general pattern at each of the 1.5-m sampling intervals. Peak density of emergence occurred at ca. 0.25 of the process time span (day 7) and declined thereafter. Emergence density was highest at the 3.5-m interval and tapered gradually towards the top of the tree and abruptly towards the bottom. The process took ca. 28 days for completion. Emergence partitioned by sex followed the same general pattern as observed for the combined sexes. The cumulative sex ratio of emerging beetles was essentially 1:1 at each height interval.Since the curves at the various height intervals were similar, emergence was described as an average process for the entire tree. The essential features of the process were retained in the average analysis. A probability distribution function defined for emergence permits calculation of the distribution of beetles from host trees provided the cumulative density is known. A frequency histogram illustrating the range in observed emergence density over a three year period was also included.Adult populations of D. frontalis available for colonization were interpreted as a single process “allocation.” The allocation process was defined by two components, re-emergence and emergence, and had the following characteristics: (1) it is continous for each tree in the infestation, (2) it is distinct for each tree, (3) it is bimodal in intensity, and (4) the components may operate together or independently. The allocation concept was used to interpret the manner in which D. frontalis infestations have been observed to develop.