Comparison of ten entomopathogenic nematodes for control of sweetpotato weevil (Coleoptera: Apionidae)

Ten entomopathogenic nematode species or strains in the families Steinernematidae and Heterorhabditidae-Steinernema carpocapsae (Weiser), Agriotos, All, Breton, Italian, and Mexican strains; Steinernema feltiae (Filipjev), N27 strain; Steinernema intermedia (Poinar); Heterorhabditis bactriophora, Poinar, HP88, and North Carolina strains; and an unidentified Heterorhabditis sp. FL2122 strain-were compared in the laboratory against the sweetpotato weevil, Cylas formicarius (F.). Although all nematodes tested could kill sweetpotato weevils, there were differences among the nematodes. Larval LC50S were low for most nematodes tested ( 1O infective juveniles per insect). The heterorhabditid nematodes included the most virulent nematode (unidentified Heterorhabditis sp. FL2122 strain), and the least virulent nematode (H. bacteriophora North Carolina strain). Heterorhabditid nematodes were more pathogenic to pupae than were steinernematid nematodes. Weevil adults were the least susceptible stage to nematode infection. With the exception of S. carpocapsae All strain, adult mortality was 6% for all nematodes. Adult mortality by All strain ranged from 25 to 60% depending on the nematode concentration applied. Male weevils accounted for 96-100% of the adult mortality by All strain. Larval mortality from nematode infection increased significantly over a 4-d period for all nematodes with the exception of S. feltiae, which caused high mortality within 24 h. Heterorhabditid nematodes produced significantly more infective juveniles per cadaver than did steinernematid nematodes. The importance of these data for selecting suitable nematodes for biological control of the sweetpotato weevil is discussed