Canadian Forest Service Publications
Spruce Budworm (Lepidoptera: Tortricidae) Oral Secretions II: Chemistry. 2015. Leclair, G.; Williams, M.; Silk, P.J.; Eveleigh, E.S.; Mayo, P.D.; Brophy, M.; Francis, B. Environmental Entomology 44(6): 15-31-1543.
Issued by: Atlantic Forestry Centre
Catalog ID: 37159
Availability: PDF (download)
As sessile organisms, plants have evolved different methods to defend against attacks and have adapted their defense measures to discriminate between mechanical damage and herbivory by insects. One of the ways that plant defenses are triggered is via elicitors from insect oral secretions (OS). In this study, we investigated the ability of second-instar (L2) spruce budworm [SBW; Choristoneura fumiferana (Clemens)] to alter the volatile organic compounds (VOCs) of four conifer species [Abies balsamea (L.) Mill., Picea mariana (Miller) B.S.P., Picea glauca (Moench) Voss, Picea rubens (Sargent)] and found that the emission profiles from all host trees were drastically changed after herbivory. We then investigated whether some of the main elicitors (fatty acid conjugates [FACs], β-glucosidase, and glucose oxidase) studied were present in SBW OS. FACs (glutamine and glutamic acid) based on linolenic, linoleic, oleic, and stearic acids were all observed in varying relative quantities. Hydroxylated FACs, such as volicitin, were not observed. Enzyme activity for β-glucosidase was also measured and found present in SBW OS, whereas glucose oxidase activity was not found in the SBW labial glands. These results demonstrate that SBW L2 larvae have the ability to induce VOC emissions upon herbivory and that SBW OS contain potential elicitors to induce these defensive responses. These data will be useful to further evaluate whether these elicitors can separately induce the production of specific VOCs and to investigate whether and how these emissions benefit the plant.
Plain Language Summary
Many studies have shown that the oral secretions of some caterpillar species contain chemical components that can cause plants to defend themselves against attack by these caterpillars. In this study, we investigated the ability of spruce budworm larvae (caterpillar stage) to alter the odors (volatile compounds) emitted by balsam fir and spruce trees. We found that the odors coming from all of the trees were drastically changed after they were fed on by the budworm. We then investigated whether oral secretions that are secreted by budworm when feeding on trees contain some of the components that are known in other caterpillar species to cause plants to emit certain odors. Budworm oral secretions were found to contain some of these important components, indicating that budworm can induce defensive responses in trees when they feed on them. The next step is to determine which of these chemical components trigger the defensive responses, causing the trees to emit certain odors that help attract natural enemies (parasites and predators) to come to the trees and attack and kill the budworm.