Abstract:
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.
