Pests of Pests of Blue Willow Trees in a Potentially Warmer World

In the words of Baffoe et al. (2012), "with the prospect of warmer temperatures as a consequence of ongoing climate change, it is important to investigate how such increases will affect parasitoids and their top-down suppression of herbivory in agroecosystems," which topic the authors set out to investigate in their study. Specifically, they examined such effects with respect to a parasitoid that afflicts a common beetle that feeds on several short-rotation species of commercially-coppiced willow trees in northern and central Europe, which trophic cascade is described in more detail by Peacock et al. (1999), Bjorkman et al. (2003) and Dalin (2011). To do so, they conducted laboratory experiments where they "studied how the performance and biocontrol efficiency of the willow 'bodyguard' Perilitus brevicollis Haliday (Hymenoptera: Braconidae) were affected at different constant temperatures (10, 15, 20, 25°C) when parasitizing a pest insect, the blue willow beetle (Phratora vulgatissima L., Coleoptera: Chrysomelidae)," which they did by focusing on "the parasitoid's thermal threshold for development, development rate, adult body size, survival rate and the herbivore's consumption rate."

In describing their results, the four Swedish scientists report that parasitism had no impact on herbivory at 10°C; but they found that "parasitoid performance (survival and development rate) generally increased with increasing temperature up to 20°C." In addition, they learned that "the feeding capacity of the studied parasitized herbivores is reduced more at high than low temperatures." Such findings, in the words of Baffoe et al., "suggest that P. brevicollis should become a better biocontrol agent if temperatures increase," which transformation should have substantial positive consequences for willow trees in northern and central Europe, as well as for the enterprise of their commercial harvesting.

Additional References
Bjorkman, C., Dalin, P. and Eklund, K. 2003. Generalist natural enemies of a willow leaf beetle (Phratora vulgatissima): abundance and feeding habits. Journal of Insect Behavior 16: 747-764.

Dalin, P. 2011. Diapause induction and termination in a commonly univoltine leaf beetle (Phratora vulgatissima). Insect Science 18: 443-450.

Peacock, L., Herrick, S. and Brain, P. 1999. Spatio-temporal dynamics of willow beetle (Phratora vulgatissima) in short-rotation coppice willows grown as monocultures or a genetically diverse mixture. Agricultural and Forest Entomology 1: 287-296.