Canadian Forest Service Publications
Spruce Budworm (Lepidoptera: Tortricidae) Oral Secretions I: Biology and Function. 2015. Eveleigh, E.S.; Silk, P.J.; Leclair, G.; Mayo, P.; Francis, B.; Williams, M. Environmental Entomology 44(6): 1641-1651.
Issued by: Atlantic Forestry Centre
Catalog ID: 37158
The potential roles of the oral secretions (OS) of spruce budworm (SBW; Choristoneura fumiferana Clemens) larvae and factors that may affect the volume of OS disgorged were investigated in the laboratory. Experiments revealed that diet-fed SBW larvae readily disgorge OS when induced (“milked”), with minimal overall cost to their development and eventual pupal weight. Exposure of conspecific larvae to OS throughout larval development negatively affected survival and male pupal weight; however, male development time was faster when exposed to OS. Female pupal weight and development time were not affected. Preliminary experiments suggested that OS had a repellent effect on a co-occurring herbivore, the false hemlock looper, Nepytia canosaria (Walker). OS produced by larvae that fed on three host tree species and on artificial diet significantly increased the grooming time of ants (Camponotus sp.), indicating that SBW OS have an anti-predator function. The volume of OS is significantly greater in L6 than in L4 or L5, with the volume produced by L6 depending on weight and age as well as feeding history at time of milking. These findings indicate that SBW OS function as both an intra- and interspecific epideictic pheromone and as an anti-predator defensive mechanism, while incurring minimal metabolic costs.
Plain Language Summary
The oral secretions (a combination of salivary gland and gut contents or regurgitant) of many caterpillar species are known to have several biological functions. In this study, we conducted laboratory experiments to determine the potential roles of the oral secretions of spruce budworm larvae (caterpillar stage), and the factors that may affect the amount of oral secretions expelled. We found that spruce budworm oral secretions have many functions in addition to their involvement in the digestion of nutrients. For example, it can serve as a spacing mechanism or repellent, not only against other budworm feeding on the same trees, but also against other caterpillar species that compete for its food. It also serves as a defensive mechanism against predators such as ants. However, the repeated demands on the production of oral secretions during these repellent and defensive actions throughout the budworm’s life time do not have a detrimental effect of its overall survival and growth. This knowledge of the functions of the oral secretions and its chemical composition (see next paper) may help us to develop new and better strategies against the spruce budworm.