The effects of the filbert weevil (Curculio occidentis) and the filbertworm (Cydia latiferreana) on Garry oak (Quercus garryana) acorn germination on Vancouver Island.
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Garry oak trees (Quercus garryana) and their associated ecosystems are among the most diverse and endangered landscapes in B.C. Garry oak acorns are susceptible to two insect species, the Filbert weevil (Curculio occidentis) and the Filbertworm (Cydia latiferreana). The objective of this study was to determine the effects of the Filbert weevil and the Filbertworm on Garry oak acorn germination on Vancouver Island. In the fall of 2005 a total of 1,985 Garry oak acorns were collected from 8 locations: three sites in Victoria, two sites in Nanaimo, two sites in the Comox Valley, and from Hornby Island. The acorns were observed for species-specific insect exit-hole damage, planted in potting soil, labeled as either insect-damaged or undamaged, then watered and observed for germination until December. The acorns were then removed from their containers, inspected, and insect damage was recorded. Five of the 8 sites indicated a trend that undamaged acorns were more likely to germinate than insect-damaged acorns. For example, the highest percent germination was 99% of undamaged acorns and 84% of insect-damaged acorns at one site in Courtenay. The highest total insect abundance based on insect exit holes, was 1.3 insects per acorn at the other Courtenay site. At this same site 66% of all acorns contained insects; this was the highest prevalence of insects of all 8 sites. The weevil is generally more abundant and prevalent than the moth; however, there is considerable variation in prevalence and abundance of insects between sites, likely reflecting site differences in tree stand age, soil type, and seasonal moisture levels. This study demonstrates conclusively that acorns damaged by insect larvae germinate into Garry oak tree seedlings. However, it also appears to indicate that the Filbert weevil and the Filbertworm negatively affect Garry oak acorn germination on Vancouver Island.