POTENTIAL IMPACT OF NATIVE NATURAL ENEMIES ON GALERUCELLA SPP (COLEOPTERA, CHRYSOMELIDAE) IMPORTED FOR BIOLOGICAL-CONTROL OF PURPLE LOOSESTRIFE - A FIELD-EVALUATION

Can resident natural enemies impede the action of herbivores introduce d for biological control of weeds, and if so, can their level of activ ity be predicted from tests that use resident herbivores as hosts? To examine these questions, exclusion experiments were done at three site s in central New York state which focused on the leaf beetle Galerucel la nymphaeae in stands of the introduced weed, purple loosestrife (Lyt hrum salicaria). This beetle is congeneric with two European species ( G. calmariensis and G. pusilla) that are being imported and distribute d in North America for biological control of purple loosestrife. Gener al predators, including the ubiquitous lady beetle Coleomegilla macula ta, preyed on G. nymphaeae eggs from late spring to the end of summer. During this period, approximately one-third of G. nymphaeae's egg mas ses were attacked, whereas the proportion of eggs within each egg mass that were damaged or consumed increased from about 50 to 90%. At all sites, the survival of G. nymphaeae larvae and pupae was lower in open than in closed cages during mid- and late summer, but not earlier. Th e presence of arthropod predators and the absence of parasitized or di seased beetles indicate that predators mere largely responsible for th e reduced survival in open cages. From these results, we predict that resident species of general predators, at times, may hinder the coloni zation or effectiveness of the European G. calmariensis and G. pusilla . Therefore, the continued use of protective cages when making introdu ctions and during subsequent distribution of these natural enemies is desirable. Moreover; the action of general predators should be conside red in subsequent evaluations of biological control efforts involving Galerucella spp. (C) 1996 Academic Press, Inc.