WITHIN-ROOT MORTALITY OF CYLAS-FORMICARIUS (COLEOPTERA, APIONIDAE) BYENTOMOPATHOGENIC NEMATODES

Within-root mortality of sweetpotato weevil, Cylas formicarius (F.), b y six strains of entomopathogenic nematodes in the families Steinernem atidae and Heterorhabditidae (Steinernema carpocapsae [Weiser] [=Neoap lectana carpocapsae, Steinernema feltiae] All and Mexican strains; Ste inernema feltiae [Filipjev] [=Steinernema bibionis] N-27 strain; Stein ernema glaseri [Steiner]; Heterorhabditis bacteriophora Poinar [=Heter orhabditis heliothidis] HP88 strain; and Heterorhabditis sp. FL2122 st rain [an undescribed nematode isolated in Florida]) was tested in seve ral buried-root bioassays. The ability of nematodes to locate and kill weevils, and the location within the root where infection occurred, w ere measured. In addition, mortality of the weevils in roots that were artificially infested in the laboratory was compared with mortality i n naturally infested roots from the field using two concentrations of one nematode (S. carpocapsae Mexican strain). In general, the heterorh abditid nematodes caused higher levels of mortality within the root th an the steinernematids. Heterorhabditis sp. FL2122 strain killed the h ighest proportion of weevils in the shortest period of time. Similar d ifferences among nematodes were seen in the inner portion (1/2 radius) of the storage roots, as well as in the outer portion. Although weevi l mortality in the artificially infested roots was greater than in the naturally infested roots, the trends in mortality were similar; we ob served increased mortality in the nematode treatments compared with th e control and no difference in mortality between the two nematode conc entrations.