Preference of an exotic wood borer for stressed trees is more attributable to pre-alighting than post-alighting behaviour

Abstract

Different mechanisms mediate host selection by insects before (pre-alighting) 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.