FIELD EFFICACY AND PERSISTANCE OF ENTOMOPATHOGENIC NEMATODES (RHABDITIDA, STEINERNEMATIDAE, HETERORHABDITIDAE) FOR CONTROL OF SWEET-POTATO WEEVIL (COLEOPTERA, APIONIDAE) IN SOUTHERN FLORIDA

The entomopathogenic nematodes Steinernema carpocapsae (Weiser) (All, S17, and S20 strains), S. feltiae (Filipjev) (= S. bibionis) (N27 stra in), Heterorhabditis bacteriophora (Poinar) (HP88 strain), and Heteror habditis sp. (Bacardis strain) were evaluated as biological control ag ents of the sweetpotato weevil, Cylas formicarius (F.), during two con secutive growing seasons in southern Florida. Two strains, S17 and S20 , were genetically selected ober 17 and 20 generations, respectively, for enhanced finding of the host scarab Popillia japonica Newman. Stei nernematid nematodes were applied as aqueous suspensions. The heterorh abditid nematodes, tested only in the second year, were applied using cadavers of greater was moth, Galleria mellonella (L.), infected with these nematodes. Abundance and damage of weevils differed among nemato de treatments. In the first experiment, S. carpocapsae All and S17 wer e most efficacious at reducing weevil damage and produced the highest percentages of marketable roots. In the second experiment, the heteror habditid nematode, HP88, was most efficacious at reducing weevil damag e to storage roots. All of the steinernematids, except S20 applied at a high rate (7.9 billion infective juveniles per ha), produced compara ble percentages of marketable roots but were less efficacious than HP8 8. In the first experiment, S. carpocapsae All and S17 persisted poorl y, whereas S. feltiae N27 persisted for >160 d after application. In t he second experiment, most nematodes were recovered at moderate levels for >120 d after application; however, only Heterorhabditis sp. Bacar dis was consistently recovered at high levels for >230 d after applica tion.