Potential of entomopathogenic nematodes as biological control agents of sweetpotato weevil (Coleoptera: Curculionidae)

The entomopathogenic nematodes Heterorhabditis bacteriophora Poinar (=H. heliothidis Khan, Brooks, and Hirschmann) (HP88 strain) and Steinernema (=Neoaplectana) carpocapsae Weiser (All and G-13 strains) were evaluated as biological control agents of the sweetpotato weevil, Cylas formicarius elegantulus (Summers). In Petri dish bioassays, all three strains were pathogenic to larvae and pupae of C. f. elegantulus. The LD50 values of C. f. elegantulus larvae were 2.6, 2.9, and 3.4 infective juveniles per insect for 'All,' 'G-13,' and 'HP88,' respectively. The LD50 values of pupae were 4.9, 5.9, and 4.8 infective juveniles per insect for these three nematodes, respectively. Virulence did not differ among strains or between life stages within each strain. Under simulated field conditions, 'G-13' was most efficacious at killing weevil larvae within infested sweet potato (Ipomoea batatas (L.) Lam.) roots followed in decreasing order by 'HP88' and 'All' nematodes. Efficacy in killing pupae within roots did not differ among the three nematodes or between life stages for each nematode. Field applications of 'HP88' and 'All' nematodes weremore effective than chemical insecticides at reducing weevil densities on plants. 'HP88' nematodes were more effective than 'All' nematodes and chemical insecticides at reducing weevil damage to fleshy roots