Within-Root Mortality of Cylas formicarius (Coleoptera: Apionidae) by Entomopathogenic Nematodes

Abstract

Within-root mortality of sweetpotato weevil, Cylas formicarius (F.), by six strains of entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae ( Steinernema carpocapsae \[Weiser\] \[= Neoaplectana carpocapsae, Steinemema Feltiae \] All and Mexican strains; Steinernema feltiae \[Filipjev\] \[= Steinemema bibionis \] N-27 strain; Steinernema glaseri [Steiner]; Heterorhabditis bacteriophora Poinar [= Heterorhabditis heliothidis] HP88 strain; and Heterorhabditis sp. FL2122 strain [an un-described nematode isolated in Florida]) was tested in several buried-root bioassays. The ability of nematodes to locate and kill weevils, and the location within the root where infection occurred, were measured. In addition, mortality of the weevils in roots that were artificially infested in the laboratory was compared with mortality in naturally infested roots from the field using two concentrations of one nematode ( s. carpocapsae Mexican strain). In general, the heterorhabditid nematodes caused higher levels of mortality within the root than the steinernematids. Heterorhabditis sp. FL2122 strain killed the highest proportion of weevils in the shortest period of time. Similar differences among nematodes were seen in the inner portion (½ radius) of the storage roots, as well as ill the outer portion. Although weevil mortality in the artificially infested roots was greater than in the naturally infested roots, the trends in mortality were similar; we observed increased mortality in the nematode treatments compared with the control and no difference in mortality between the two nematode concentrations.