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UBC Theses and Dissertations

Galling adelgids : gall formation, developmental morphology, characterization, and the genetic susceptibility of spruce Bains, Babita


Adelgids (Hemiptera: Adelgidae) are a small group of insects with complex life cycles and can threaten seed production in British Columbia (BC). Adelgids induce galls on the reproductive and vegetative shoots of spruce trees, reducing the number of future cone sites. Additionally, feeding on the cones and needles of alternate conifer hosts can reduce seed extraction efficiency, and cause discoloration and twisting of needles. Seed orchards are intensively managed for frequent and abundant seed production; hence losses incurred by adelgid pests are of high importance. Considering the complexity of insect-galler systems, there are many unanswered questions regarding the basic biology and habits of adelgids. My research elucidates the influence of two adelgid life stages, the fundatrix and her offspring the gallicolae, through the use of manipulative laboratory experiments and botanical histological processes. It is evident that fundatrices induce the gall formation process and gallicolae activity completes gall formation. Considering the fundatrix is required to stimulate galling it would be sufficient to include only fundatrices in a monitoring system. Additionally, I tested the theory that susceptibility to adelgid induced galling is under genetic control in spruce. Strong evidence of genetic control of susceptibility was observed with modest individual and high half- and full-sib family narrow-sense heritabilities of 0.17±0.09, 0.87±0.04, and 0.61±0.16, respectively. Breeding values for parental susceptibility to adelgid attack ranged between 0.25 and 0.76, indicating that selection for reduced susceptibility would be possible. These results suggest that adelgid galling susceptibility could be used as a screening criterion for parental inclusion in future seed orchard establishment. Furthermore, I attempted to associate structurally unique galls with the inducing adelgid species. Detailed associations of adelgid species and their galls have not been rigorously determined. Rearing of gallicolae alates from various galls suggests that there can be a wide range of variation in the structure that a single species induces. Characterization of galls may allow orchard managers to understand what adelgid species are present and possibly avoid the taxonomic expertise required to identify adelgids.

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