Natural biological control of the pine processionary moth Thaumetopoea pityocampa (Den. & Schiff.) by the Argentine ant Linepithema humile (Mayr) in Portugal

Abstract

1 Defoliation by larvae of the pine processionary moth, Thaumetopoea pityocampa, is negligible in stands of Pinus pinaster colonized by the Argentine ant Line-pithema humile which preys fiercely on the young moth larvae. In contrast, such damage is widespread where pine plantations are colonized by native ants, pre-dominantly Tapinoma nigerrimum and Lasius niger, which seemingly disregard the larvae. 2 Where L. humile- and native ant-occupied sectors adjoin, there is a 20-50m overlap in the transition area between L. humile- and native ant-occupied pines. This was most evident in a>500ha plantation where there was severe or very severe T. pityocampa attack in native ant sectors contrasting with none in adjoining L. humile sectors. 3 Predation by L. humile is no doubt enhanced by its existence as super-colonies over very large areas, by its foraging activity and recruitment on trees throughout the time when T. pityocampa and other prey are present, and by honeydew-producing Homoptera which help retain foraging L. humile workers in pine tree crowns. 4 The role of L. humile could be enhanced by cultivations that disturb the soil and restrain ground vegetation.