Graduate Thesis Or Dissertation
 

The biologies of two hemlock barkbeetles in western Oregon

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  • The objectives undertaken in this study were to investigate the biologies and potential economic importance of Pseudohylesinus tsugae Swaine and P. grandis Swaine in young coastal stands of western hemlock (Tsuga heterophylla (Rafn.) Sarg.). The life and seasonal histories of P. tsugae and P. grandis and the association of these two scolytids with the hemlock bark maggot (Cheilosia alaskensis Hunter) are presented. Both P. tsugae and P. grandis were found to have one generation a year with two broods. Both species had four larval instars. P. grandis overwintered either as a fourth instar larva or as a teneral adult. P. tsugae usually overwintered as a fourth instar larva. Within thinned stands of western hemlock P. tsugae preferred fresh stumps for breeding material, whereas P. grandis preferred fresh slash. The teneral adults of both P. tsugae and P. grandis fed in the inner-bark region of standing live host trees before initiating egg galleries in suitable breeding material. Within the thinned stands these feeding sites provided entry to the cambial region of the tree for the hemlock bark maggot. Both the number of maggot infestations and Pseudohylesinus spp. feeding sites within a stand increased after the stand was thinned. A potential method of control of both P. tsugae and P. grandis and the hemlock bark maggot was found.
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file details McGheheyJohnHoward1967.pdf 2017-08-14 Pubblico Scaricare