Abstract
A manipulative field study was carried out to determine whether the foliar endophyte fungus, Phialocephala scopiformis DAOM 229536, decreased the performance of eastern spruce budworm, Choristoneura fumiferana larvae developing on white spruce trees. Overwintered second-instar budworm larvae from a laboratory colony or from a wild population were placed on endophyte positive or negative trees one or two weeks before budburst. The presence of the endophyte in the needles reduced the survival of C. fumiferana from both a wild population and a laboratory colony. Survival for budworm juveniles up to pupation and to adult emergence was 13% and 17% lower, respectively, on endophyte positive trees. The endophyte did not influence the size or sex of survivors and budworm survival was not influenced by any two- or three-way interactions. Budworm survival was higher for wild than for laboratory-reared budworm and for budworm placed on trees a week before budburst. This may be the first field study to demonstrate the efficacy of an endophytic fungus against wild individuals of a major forest insect pest. The efficacy of the endophyte at low larval densities suggests that it could be a useful tactic to limit spruce budworm population growth in the context of an early intervention strategy.
Highlights
Mutualistic interactions between fungi living within leaf tissues and their host plants are common [1]
These results suggest that inoculation of white spruce trees with P. scopiformis could reduce tree susceptibility to spruce budworm during outbreaks
The endophyte was as effective against larger, wild budworm as it was against budworm from a laboratory colony
Summary
Mutualistic interactions between fungi living within leaf tissues (endophytes) and their host plants are common [1]. Most of the effect was attributed to the presence of the anti-insect toxin rugulosin [10] Building on those studies, we recently demonstrated a similar effect on budworm developing on white spruce trees that had been inoculated with the endophyte more than 10 years earlier [11]. The reduction in budworm survival was highest for larvae developing in the mid and upper crown of trees, the most important crown region for photosynthesis and tree growth. These results suggest that inoculation of white spruce trees with P. scopiformis could reduce tree susceptibility to spruce budworm during outbreaks
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