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The influence of larval diet and microsporidian infection on life history traits of the forest tent caterpillar, Malacosoma disstria Hübner (Lepidoptera: Lasiocampidae)

  • Author / Creator
    Preti, Flavio
  • The forest tent caterpillar (FTC), Malacosoma disstria Hübner (Lepidoptera: Lasiocampidae), is an important ecological disturbance factor of deciduous hardwood trees in North America. Disturbance is greater during outbreaks; a cyclical phenomenon in which large numbers of FTC larvae cause extensive defoliation to host trees. Outbreaks are linked to density-induced alterations of food quality and/or quantity, and increased entomopathogen abundance. Variation in FTC larval diet is known to affect life history traits and resource allocation to flight and reproduction in adult moths. Furthermore, differences in phytochemistry among host plants can alter resistance to entomopathogens. In this thesis, I use different approaches to investigate the tritrophic interaction of larval food source, FTC, and the microsporidian parasite of FTC, Nosema disstriae (Microsporida: Nosematidae). First, I examined the effects of qualitative and quantitative manipulations of an artificial larval diet and microsporidian infection by direct inoculation of FTC on the development time, cocoon production and weight, and alterations in allometric relationship between wing area (mm2) and body weight (mg). Quantitative food manipulation simulated density-induced food stress associated with high population density. Qualitative manipulation of larval diet included supplementation of artificial diet with 1% lyophilized foliage of trembling aspen, Populus tremuloides Michx (Malpighiales: Salicaceae), the main host of FTC in Canada. Microsporidian infection was administrated via inoculation at third instar larva. In a second experiment, I focused on the effects of larval host and natural infection by microsporidia of FTC on adult body size (wing area) and fitness. Forest tent caterpillar larvae were reared on two host species, trembling aspen and sugar maple, Acer saccharum Marshall (Sapindales: Sapindaceae). Results from my studies suggest larval diet does not interact with microsporidian infection to affect adult life history traits and resource allocation in FTC, although diet and infection alone influenced life history traits and resource allocation. Microsporidian infection inhibited cocoon production, likely as result of heavy infection in the silk glands. Severe microsporidian infection was associated with reduced wing area and the loss of allometric relationship between wing area and body weight, which implies infection by microsporidia can alter FTC evolutionary trade-offs between reproduction and dispersal. In contrast to other insects, microsporidian infection was not associated with wing malformation in FTC. Addition of lyophilized trembling aspen foliage to the larval diet led to increased wing malformation, longer development time, and loss of the allometric relationship between wing area and body weight. These effects are likely the result of aspen secondary metabolites in the diet. Partial starvation resulted in increased development time, reduced adult size, and loss of the allometric relationship between wing area and body weight, suggesting density-related nutritional stress may affect dispersal by flight in FTC. The larval host study provides further evidence that trembling aspen is a more suitable host for FTC than sugar maple. My studies are the first to assess the potential interaction between larval diet and microsporidian infection in FTC. The results suggest host phytochemistry and density-induced resource limitation do not interact with microsporidian infection in FTC, but they likely work in an additive fashion to influence life history traits that contribute to population cycling in this species.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-7rn1-rt44
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.