Interaction of Apanteles fumiferanae (Hymenoptera: Braconidae) and Nosema fumiferanae (Microsporidia) parasitizing spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae)

Abstract

The relationship between a braconid parasitoid, Apanteles fumiferanae, and a microsporidian pathogen, Nosema fumiferanae, two larval parasites frequently coincident in the spruce budworm, Choristoneura fumiferana, was examined in the laboratory. When Apanteles was reared in spruce budworm infected with high levels of Nosema (i.e., more than 20 × 106 spores/mg dry weight), there was a slight reduction in the within-host rate of development of larval female Apanteles, but survival, within-cocoon rate of development, cocoon weight, and adult longevity were not affected. There was no evidence that any stage of Apanteles was infected with spores of Nosema. A few adult female parasitoids were found to carry spores of Nosema on their integuments but it is unlikely that Apanteles is an important vector of the microsporidian. We conclude that these natural enemies of budworm do not interact significantly in their common host. The implications for population dynamics of the spruce budworm and mass rearing of Apanteles are discussed.

Microsporidia Biological Control Agents and Pathogens of Beneficial Insects

“…Apanteles fumiferanae is a solitary endoparasitoid of the spruce budworm, Choristoneura fumiferana, in Canada, and in any given year, between 10 and 30% of natural spruce budworm populations are parasitized (see Nealis & Smith 1987). The microsporidium Nosema (formerly Perezia) fumiferanae infects much of the spruce budworm population in southern Ontario, but the frequency of infection seems to increase with high densities of spruce budworm in localized areas (see Nealis & Smith 1987).…”

“…The microsporidium Nosema (formerly Perezia) fumiferanae infects much of the spruce budworm population in southern Ontario, but the frequency of infection seems to increase with high densities of spruce budworm in localized areas (see Nealis & Smith 1987). N. fumiferanae infects several tissues of spruce budworm larvae and adults (Thomson 1955;Percy 1973), but the effects of this pathogen on its host depend upon the intensity of infection.…”

“…Spores of N. fumiferanae are confined to the gut contents of A. fumiferanae larvae but do not invade any tissues (Thomson 1958a;Nealis & Smith 1987). A. fumiferanae larvae have a blind gut where food is stored to last through pupation.…”

“…Although microsporidian spores are observed in association with A. fumiferanae adults, Spider prey Oligosporidium arachnicolum Unknown these are not found on parasitoid adults that have been washed in detergent and saline. It is likely that spores are only on the external surface of adult parasitoids (Nealis & Smith 1987). Microsporidian spores appear to be carried on the outside of female A. fumiferanae adults but not males.…”

“…Despite this observation, pathogen prevalence and intensity of N. fumiferanae are low, and it is unlikely that the parasitoid is an important vector of the pathogen in spruce budworm populations. There is also little evidence that the microsporidium and the parasitoid are associated in natural populations of spruce budworm at a level that would be necessary for successful horizontal or vertical pathogen transmission (Nealis & Smith 1987).…”