Field Efficacy and Persistence of Entomopathogenic Nematodes (Rhabditida: Steinernematidae, Heterorhabditidae) for Control of Sweetpotato Weevil (Coleoptera: Apionidae) in Southern Florida

The entomopathogenic nematodes Steinernema carpocapsae (Weiser) (All, S17, and S20 strains), S. feltiae (Filipjev) (= S. bibionis) (N27 strain), Heterorhabditis bacteriophora (Poinar) (HP88 strain), and Heterorhabditis sp. (Bacardis strain) were evaluated as biological control agents of the sweetpotato weevil, Cylas formicarius (F.), during two consecutive growing seasons in southern Florida. Two strains, S17 and S20, were genetically selected over 17 and 20 generations, respectively, for enhanced finding of the host scarab Popillia japonica Newman. Steinernematid nematodes were applied as aqueous suspensions. The heterorhabditid nematodes, tested only in the second year, were applied using cadavers of greater wax moth, Galleria mellonella (L.), infected with these nematodes. Abundance and damage of weevils differed among nematode treatments. In the first experiment, S. carpocapsae All and S17 were most efficacious at reducing weevil damage and produced the highest percentages of marketable roots. In the second experiment, the heterorhabditid nematode, HP88, was most efficacious at reducing weevil damage to storage roots. All of the steinernematids, except S20 applied at a high rate (7.9 billion infective juveniles per ha), produced comparable percentages of marketable roots but were less efficacious than HP88. In the first experiment, S. carpocapsae All and S17 persisted poorly, whereas S. feltiae N27 persisted for >160 d after application. In the second experiment, most nematodes were recovered at moderate levels for >120 d after application; however, only Heterorhabditis sp. Bacardis was consistently recovered at high levels for >230 d after application.