Seeing the forest through the trees: differential dispersal of Hylobius warreni within modified forest habitats

Hylobius warreni Wood, also known as the Warren root collar weevil, is a flightless insect that feeds on conifers throughout the boreal forests of Canada. Mature trees typically can withstand feeding, but larval feeding around the root collar may cause mortality to young trees. Recently, a large outbreak of mountain pine beetle (Dendroctonus ponderosae Hopkins) has killed a high proportion of mature lodgepole pine (Pinus contorta Douglas variety latifolia) across British Columbia, Canada. This raises concerns that adult weevils may migrate from mature forests with reduced host pools into adjacent young forests that had been salvaged and replanted. To study movement of these walking weevils in different habitat types, we constructed three research plots consisting of various combinations of live-, dead-, and mixed (i.e., live and dead)-tree habitats. We observed dispersal patterns of individually labeled insects using a novel insect trap attached to the base of trees. Approximately 35% of insects were recaptured over 1 mo. Weevils were least likely to be recaptured proximate to the release location when released in a habitat with dead trees. Movement rates therein were almost double the rates of insects moving through live- or mixed-tree habitats. Our findings support the hypothesis that H. warreni may disperse out of habitats with dead trees into areas with higher proportions of green trees. Our findings are discussed in the context of habitat discrimination and potential increases in herbivory by H. warreni in western Canada given salvage harvesting activities after outbreaks of mountain pine beetle.