Canadian Forest Service Publications
Preference of an exotic wood borer for stressed trees is more attributable to pre-alighting than post-alighting behaviour. 2013. Flaherty, L.; Quiring, D.T.; Pureswaran, D.; Sweeney, J.D. Ecological Entomology 38: 546-552.
Issued by: Atlantic Forestry Centre
Catalog ID: 35119
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- Different mechanisms mediate host selection by insects before (prealighting) versus after (post-alighting) landing on potential hosts, but few studies distinguish pre- and post-alighting behaviour, particularly for wood borers.
- This study evaluates pre- and post-alighting host selection by Tetropium fuscum (F.) (Coleoptera: Cerambycidae), a Palearctic wood borer that was recently introduced to Halifax, Nova Scotia.
- We evaluate whether T. fuscum select stressed (i.e. girdled) over healthy red spruce, Picea rubens Sarg. (Pinaceae), trees for oviposition, as predicted by the preference–performance hypothesis (PPH). The landing rates of the native congener, Tetropium cinnamopterum Kirby (Coleoptera: Cerambycidae), and parasitoids of Tetropium spp. were also quantified.
- Tetropium fuscum consistently preferred girdled over healthy trees. Adults landed more than 10 times more frequently (11.0 ± 1.5 versus 0.6 ± 0.2 adults per tree), and females laid more than 3 times as many eggs (130 ± 23 versus 38 ± 13 eggs per bolt), on girdled compared with healthy trees. As T. fuscum survival and rate of development is greater on girdled than on healthy trees, these results support the PPH.
- Tetropium fuscum rarely made maladaptive choices pre-alighting, but post-alighting oviposition on hosts on which performance is relatively lower was more common. Selection of high-quality (e.g. girdled) hosts by female T. fuscum is therefore more attributable to pre-alighting than post-alighting behaviour.
Plain Language Summary
The brown spruce longhorn beetle, Tetropium fuscum, (BSLB) is an invasive species from Europe that has established in Nova Scotia and is slowly spreading westward. In Europe it infests severely weakened Norway spruce but in Canada it has infested and killed apparently healthy spruce. In previous studies in which we placed eggs or adult beetles on trees (i.e., the beetles had no choice) we found that BSLB survival was much greater on stressed trees than on healthy trees. The “preference-performance hypothesis” predicts that when given a choice, females will prefer to lay eggs on trees on which their progeny have greater survival. We tested this prediction with the BSLB by comparing healthy versus stressed spruce for the numbers of BSLB that landed on the trees and the number of eggs laid per tree. We found that ten times as many BSLB landed on stressed spruce than on healthy spruce, and once they had landed, laid three times as many eggs on stressed spruce than on healthy spruce. These results support the preference-performance hypothesis, i.e., female BSLB made smart choices when looking for trees in which to lay their eggs. Our results also showed that these choices were made largely before landing on the trees, probably using olfactory cues. Finally, the results also suggest that healthy spruce trees are at much lower risk of attack by the BSLB than are stressed spruce.