Graduate Thesis Or Dissertation
 

The biologies of predators (Coleoptera: Cleridae) of the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins (Coleoptera : Scolytidae), in western Oregon

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  • Six species of Cleridae, including Enoclerus spegeus Fabricius, E. lecontei Wolcott, E. schaefferi (Barr), E. eximius Mannerheim, Thanasimus undatulus Say, and an undescribed species of Enoclerus, were found on Douglas-fir in western Oregon. E. sphegeus was the only clerid of the six species studied which was primarily associated with the Douglas-fir beetle, as the other clerids occurred more often with Scolytus unispinosus or other small scolytids. E. sphegeus and T. undatulus each had a life span of two years, the first year of which was spent in the immature stages. E. sphegeus and T. undatulus adults emerged during the latter part of the summer, apparently overwintered in bark crevices, and appeared on Douglas-fir beetle-infested trees the following spring. Both species survived as adults approximately a year in the field, and E. sphegeus lived up to nearly a year and a half in the laboratory. E. lecontei adults emerged throughout the summer, survived no more than two months in the laboratory, and gave no indication of overwintering in the adult stage. Clerids mated frequently throughout their adult life. Mating appeared to be stimulated by a pheromone produced by the females. Two larval instars were found in E. sphegeus, three in T. undatulus, E. lecontei, and Enoclerus sp., and four in E. schaefferi, although none of the E. schaefferi larvae pupated. E. sphegeus larvae fed on all stages of Douglas-fir beetle brood during the first instar, and fed mostly on Douglas-fir beetles from the third instar to callow adult in the early part of the second instar. After the first few weeks, most second instar larvae did not feed, but left the Douglas-fir beetle galleries and remained relatively inactive throughout the winter and spring in pupal cells, constructed in the outer bark of infested trees or in chunks of partly decayed bark on the ground, until the following July or August when they pupated. A few prepupal larvae in the outer bark were parasitized by a species of Ichneumonidae. E. sphegeus adults apparently did not consume their potential of Douglas-fir beetles in the field due to lack of available Douglas-fir beetle adults throughout most of the year. E. sphegeus larvae were rather ineffective as predators, since they occurred mainly where Douglas-fir beetle gallery density was high, and merely reduced competition of Douglas-fir beetle brood rather than causing a decrease in the population.
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