Host range, attack dynamics, and impact of Cryptorhynchus lapathi (Coleoptera: Curculionidae) on Salix (Salicaceae) spp.

Abstract

AbstractThe poplar and willow borer, Cryptorhynchus lapathi (L.), known to be present in British Columbia since 1923, primarily attacks species of Salix L. (Salicaceae) and Populus L. (Salicaceae). Larvae bore into stems, causing them to break easily. The impact of the weevil has been rising in recent years because of the increasing importance of poplar and willow from both economic and ecological perspectives. We conducted a study at 45 locations in British Columbia to determine host use among native Salix spp. and the between- and within-tree dynamics of C. lapathi. There were 11 new host records, but the incidence of attack was similar among species. Attacked trees were larger in general and had more dead wood and stems, more adventitious branches per stem, more total breaks per stem, and more naturally caused breaks per stem than their attack-free neighbours. Breaks caused by C. lapathi tended to be slightly larger in diameter and lower on the stem than naturally caused breaks. Bases of stems were preferentially attacked, and C. lapathi selected large stems in which to oviposit. As large attack-free trees become less abundant, weevils apparently start to attack small-diameter stems. Although C. lapathi is adversely affecting the health of willows in British Columbia, there is no evidence that any Salix species is threatened by weevil-caused extinction.