Dispersal of Pissodes strobi in putatively resistant white spruce in Vernon, BC

Abstract

White pine weevil Pissodes strobi behaviour was observed in a five-year-old plantation of white spruce in Vernon, British Columbia. Seasonal weevil-host interactions were monitored in four susceptible and four putatively resistant reciprocal cross family pairs in three of five replicates. Classification of susceptibility to weevil attack was based on previous weevil attack history. Performance of eight reciprocal cross pairs was ranked as a function of visitation, oviposition and brood establishment resulting in top-kill. The four putatively resistant family crosses ranked 1 to 4 for resistance to weevil attack, while the four susceptible crosses were ranked 5 to 8 and were consistently attacked. Seasonal and diurnal weevil movement was monitored using mark-recapture techniques. Diurnally, weevils moved within the tree. Feeding occurred at dawn in the leader and upper laterals after which weevils moved down the tree into the forest floor during the high mid-summer temperatures. Later in the season weevils fed in mid-morning on the leader and on the under-sides of lateral branches. A dispersal index was developed to describe seasonal movement. Weevils did not move far throughout the season. Overall dispersal index for both males and females was less than 0.24 m, suggesting that on average, weevils do not move further than the adjacent tree throughout the season after mating and oviposition. Key words: Dispersal, pest management, Pissodes strobi, resistance, silviculture, white spruce