LABORATORY STUDIES OF THE EFFICACY OF STEINERNEMATID NEMATODES AGAINST THE PLUM CURCULIO (COLEOPTERA, CURCULIONIDAE)

Efficacy of the entomopathogenic nematode Steinernema carpocacapsae (W eiser) for the control of plum curculio, Conotrachelus nenuphar (Herbs t), on apple was evaluated under laboratory conditions. When 50, 100, 200, or 400 nematodes per plum curculio larva were pipetted in 1 ml of water onto moistened filter paper in petri dishes containing 20 larva e, average larval mortality was 71.8, 80.6, 91.6, and 95.1%, respectiv ely, after 3 d of incubation at 25-degrees-C. In a comparison of four strains applied at 50, 100, and 200 nematodes per larva, S. carpocapsa e strain All was more effective at the rate of 50 per larva than three other strains, and was equal to the effect of S. feltiae (Filipjev) ( =S. bibionis, Biosys strain no. 27) applied at the rate of 100 and 200 per larva. Maximum mortality caused by the Mexican and Kapow strains of S. carpocapsae was only 50.0 and 27.5%, respectively, irrespective of rate. When S. carpocapsae All was sprayed on or mixed with a 5-cm l ayer of soil at a rate equivalent to 10 x 10(9)/ha, 90.8 and 87.6%, re spectively, of the 12-15 plum curculio larvae added were killed after incubation for 3 d ar 25-degrees-C. Natural sods (25 by 30 by 5 cm) fr om an orchard floor were sprayed or drenched with S. carpocapsae All a t the rate of 10 x 10(9)/ha in 600 ml of water 2 d before 25 plum curc ulio larvae were added. After 3 d, larval mortality was 73.4%. Reversa l of the inoculation sequence by addition of plum curculio first, foll owed by nematodes, gave similar control (76.4%). In sods treated with nematodes only four of the 55 nontarget insect larvae and adults conta ined nematodes; we found no infestation in nontarget insects from untr eated sods. When Galleria mellonella (L.) larvae were used as bait, we showed that the sod soil contained naturally occurring entomopathogen ic nematodes. These results show that plum curculio is highly suscepti ble to entomopathogenic nematodes in the laboratory.