Canadian Forest Service Publications
Host-choice by a specialist folivore reflects trade-offs between foliage quality and 1 parasitism risk. 2021. Stead, L.; Heard, S.B.; Johns, R.C. Ecological Entomology 46: 4
Issued by: Atlantic Forestry Centre
Catalog ID: 40578
Availability: PDF (download)
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The spruce budworm, Choristoneura fumiferana Clem., is an important outbreaking pest of balsam fir, Abies balsamea (L.) Mill, and black spruce, Picea mariana (Mill.) Britton, Sterns & Poggenb., throughout the boreal forests of North America.
Despite several studies reporting higher performance for larvae on balsam fir versus those on black spruce, many females still lay eggs on spruce. In this 2-year study, we explored possible tri-trophic trade-offs associated with host selection taking into account both larval overwintering and feeding periods.
Based on field surveys, parasitism rates were significantly higher for overwintering larvae on balsam fir than on black spruce in 2017.
Field bioassays confirmed past studies showing 21% higher larval survival on balsam fir versus black spruce, especially when larval emergence was synchronized with host budburst.
Considering both overwintering and feeding survival, overall spruce budworm performance was nearly equal between hosts, though larvae gained some advantage on balsam fir if larval feeding was synchronized with budburst.
These results suggest that female egg lay on both hosts may be a ‘bet-hedging’ strategy that balances trade-offs between higher parasitism and higher foliage quality on different potential host species.
Plain Language Summary
The spruce budworm is a forest pest in eastern North America. It feeds on balsam fir and spruce, both of which are common trees in New Brunswick. This paper assesses the cost and benefits for spruce budworm to hibernate and feed on these two hosts. This is novel research as previous studies have not compared these two life stages, but have rather looked at them separately. We found that one host is better for hibernating, whereas the other is better as a host to feed.