Graduate Thesis Or Dissertation
 

Diurnal and seasonal flight patterns of bark beetles (Coleoptera : Scolytidae) associated with Douglas-fir forests of western Oregon

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  • The study was undertaken to determine the seasonal and diurnal flight patterns of scolytid beetles inhabiting a second growth forest of Douglas-fir (Pseudotsuga menziesii (Mirb.)Franco) in western Oregon. Air temperatures, relative humidity, light intensity, and wind velocities were recorded for evaluation of their influence on flight activity. The insects were trapped in flight by six mechanically powered rotary nets. These devices were arranged 110 - 140 feet apart in shaded and relatively exposed positions reaching from the base to the crest of a small ridge. Flights were in some cases related to patterns of emergence from caged logs. The study was conducted during the spring and summer of 1963 and 1964, with some pertinent differences in seasonal flight activity noted. Due to an abundant host supply in 1963, greater numbers of many species were caught in 1964. Twenty-four scolytid species were identified from net collections in 1964, whereas only 15 species were collected the previous year. With the exception of a single species, Scolytus unispinosus LeConte, which overwinters in an immature stage, the initiation of seasonal flight depended on sufficiently high temperatures to induce flight. A wide range of air temperatures necessary to initiate flights of the respective species was observed. These differences in temperature thresholds resulted in a seasonal succession of species found in flight. While changes in relative humidity caused no apparent effects on flight, light intensity was especially influential for certain species. Of 11 species in sufficient abundance for detailed study, six (Pseudohylesinus nebulous (LeConte), P. grandis Swaine, Trypodendron lineatum (Olivier), Phloeosinus sequoiae Hopkins, P. punctatus LeConte, and Scolytus unispinosus) flew during the mid-day hours. The remaining five (Hylastes nigrinus (Mannerheim), H. ruber Swaine, Gnathotrichus sulcatus (LeConte), G. retusus (LeConte), and Dryocoetes autographus (Ratzeburg) ) exhibited crepuscular flight patterns, flying in greatest numbers when light intensities were below 1000 foot candles.
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