Graduate Thesis Or Dissertation
 

The biologies of two dipterous predators of Dendroctonus pseudotsugae Hopkins (Coleoptera : Scolytdae) in western Oregon and Washington

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  • The objectives of this study were: 1) to learn the life history and habits of Medetera aldrichii Wheeler and a Lonchaea sp. in association with the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, in western Oregon and Washington; 2) to determine if the larvae of M. aldrichii were predaceous on the Douglas-fir beetle; and 3) to determine the effect of elevation and exposure on the emergence of M. aldrichii. Seasonal histories of M. aldrichii and the Lonchaea sp. in association with the Douglas-fir beetle in western Oregon and. Washington are presented. M. aldrichii was found to have only one generation per year while the Lonchaea sp. had one and a partial second generation. Third-instar larvae of M. aldrichii killed larvae and . pupae of the Douglas-fir beetle in the laboratory, but they would not kill adults, Third-instar larvae of the Lonchaea sp. would not kill any of the stages of the Douglas-fir beetle. The second instar of M. aldrichii is described for the first time, and all the immature stages of the Lonchaea sp. are described. Larval instars of M. aldrichii as well as the Lonchaea sp. may be separated by measuring the lengths of their cephalo-pharyngeal skeletons, which almost doubled with each succeeding instar. Emergence dates of M. aldrichii were affected by the elevation of infested trees as well as their degree of exposure to direct radiation, In an emergence study utilizing three field cages, emergence began first on May 23, 1963, in a field cage exposed to direct radiation at an elevation of 1400 feet, progressed to an unexposed cage at the same elevation, and commenced last on September 19 in an unexposed cage at an elevation of 2000 feet.
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