Biology and behaviour of the white pine weevil pissodes strobi (Peck) in white spruce
Creators: name: McIntosh, Rory L.
Publisher: name: University of British Columbia
Year: 2009

description: The white pine weevil Pissodes strobi (Peck) (Coleoptera: Curculionidae) is a major pest in spruce plantations in western Canada. Larvae, mining down the axis of the tree, girdle the leader killing at least 2 and sometimes up to 4 years' growth. Existing knowledge of the biology and behaviour of P. strobi has been derived mostly from studies in eastern white pine and Sitka spruce hosts. Interior spruce (Picea engelmannii Parry, P. glauca Moench. Voss. and their hybrid swarms) are extremely important to the B.C. forest economy. Although no operational control exists, current research into genetic resistance is promising. Results of research at the Kalamalka Research Station in Vernon, B.C., suggest a substantial genetic variation exists in weevil preference to different spruce families. However, information of P. strobi bionomics on interior spruce host trees is seriously lacking. The major focus of this thesis was to determine detailed information of the bionomics of P. strobi on white spruce. Host-selection behaviour and host resistance mechanisms should be determined before an active breeding program to produce weevil-resistant trees can be initiated. At Kalamalka Research Station studies were initiated in a 9 year-old plantation of interior spruce which comprised 45 reciprocal cross pairs in five replicate blocks. Surveys were conducted in an additional 10 sites around B.C. The thesis addresses three main areas: Firstly, P. strobi biology, including development and population dynamics in white spruce; secondly improved knowledge of diurnal and seasonal dispersal behaviour; and thirdly, assess aspects of the interaction between P. strobi and its white spruce host. Leader dissections were conducted to monitor P. strobi development over time. Meteorological data were collected to test the accuracy of the existing degree-day model used to predict P. strobi development. Field studies showed that a 7.2°C threshold temperature gives a good estimate of weevil emergence if internal leader temperature was used to calculate heat sum. Diurnal and seasonal P. strobi movement was determined by mark-release-recapture techniques. Between 1994 to 1996, 1,463 P. strobi found at Kalamalka were captured, marked and returned to the plantation then tracked during the active season. Daily movement was investigated in a series of four diurnal studies. Seasonal movement was assessed by tracking marked weevils over time using regular systematic surveys. On average, peak dispersal occurred in the spring, and most of the time P. strobi remain very close to the tree where they were last seen. From 30 to 50% of overwintered weevils moved long-distances ("hoppers"), in some cases up to 100 m. Peak movement by these individuals occurs in the post-oviposition period in mid-June. Dispersal is hypothesized to occur mainly by crawling and through a series of long-distance hops to adjacent trees. Ground-based dispersal was monitored using Townes malaise traps. To assess immigration and emigration an existing malaise trap design was modified to collect weevils dispersing by flight. Weevils could be trapped individually in all four cardinal directions as well as those moving to the top and base of the trap. These traps were placed around the plantation at a height of 2 m and 3 m. It was concluded that flight is not a major form of dispersal since too few weevils were caught in the trapping study for analysis. No strong weevil flight was seen during the three years of study. Two groups of movement behaviours were identified, close range and those dispersing distances greater than 18 m ("hoppers"). Host-weevil interaction was surveyed in four putatively resistant and four susceptible reciprocal family crosses. Surveys were conducted in three of the five replicates and in the 10 sites around B.C. Samples were taken from the plantation at Kalamalka to examine the hypersensitive response of the host to observed weevil attack. Trends of demonstrated resistance were seen consistently in two years of study. Performance of the eastern North American crosses was ranked consistently higher than that of western crosses. Key Words: Curculionidae, biology, dispersal, heat sum, mark-recapture, Pissodes strobi, resistance, spruce, trapping.