Attractiveness of three weed species to polyphagous predators and their influence on aphid populations in adjacent lettuce cultivations

The utilization of olfactory responses of predators and ­parasitoids to the allelochemicals emitted by phytophagous arthropods and their host plants is becoming more important in biological pest control. The effects of three weed ­species, i.e. wormwood Artemisia vulgaris L., tansy Tanacetum vulgare L. and stinging nettle Urtica dioica L., which were planted as accompanying vegetations into a lettuce field, were examined for the predatory species Coccinella septempunctata L., Adalia bipunctata (L.), Propylea quatuordecimpunctata (L.) (Coleoptera, Coccinellidae) and Chrysoperla carnea (Steph.) (Neuroptera, Chrysopidae), as well as for aphids during the summer of 2000. The presence of weeds significantly increased the density of adults and larvae of the predators on the lettuce plants in relation to the control (lettuce field without weeds). However, the differences remained smaller for eggs and pupae. C. septempunctata tended to be the most abundant species, followed by P. quatuordecimpunctata. Remarkable differences among the attractiveness levels of the weeds in the 3 treatments were not observed. The increased populations of predators were accompanied by significantly reduced infestation rates with aphids in the treatments in relation to the control. Myzus persicae Sulzer was in general the most abundant aphid species followed by Nasonovia ribisnigri Mosley and Macrosiphum euphorbiae Thomas. The results of the present study are discussed with respect to the management of agroecosystems and the use of weeds in biological control.