Screening of sitka spruce (Picea sitchensis) seedlings for resistance to the white pine weevil (Pissodes strobi) in a caging experiment
2000
Klimaszewski, J. | Bernier-Cardou, M. (Canadian Foest Service, Sainte-Foy (Canada). Natural Resources Canada) | Cyr, D. | Alfaro, R. | Lewis, K.
Four weevil pressure treatments (4, 8, 16 and 24 weevils per cage, equivalent to 1/2, 1, 2 or 3 weevils per seedling) were tested in a caging experiment on two-year-old potted Sitka spruce seedlings (emblings : seedlings derived via somatic embryogenesis) or seedlings from weevil-susceptible (control) and -resistant sources. An increase in weevil pressure resulted in an increase in the numbers of both feeding punctures and adult weevils present on the seedlings, at least on susceptible ones. Over a five-week period, at the highest weevil pressure, an average of 0.95 weevils per seedling was observed on weevil-resistant seedlings versus 3.45 weevils per seedling on susceptible ones. Neither the number of feeding nor oviposition punctures was useful in detecting seedling resistance. However, differences did occur in the number of adults emerging from weevil-resistant and weevil-susceptible seedlings. A total of 37 weevil adults emerged: 31 from weevil-susceptible seedlings and 6 from a single weevil-resistant seedling. Larval feeding was the main cause of seedling mortality, and adult overfeeding was a secondary factor. Fourteen seedlings were killed, 12 of which were susceptible and two resistant. This experiment indicated that the main mechanisms of resistance in the seedlings were blockage of the host selection process and toxicity to larvae and eggs. We concluded that caging experiments, where weevils have a choice between resistant and susceptible seedlings, provide a useful tool for mass screening of resistant clonal material.
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