Entomopathogenic nematodes and other natural enemies as mortality factors for larvae of Diaprepes abbreviatus (Coleoptera : curculionidae)

Parasitism and persistence of three species of entomopathogenic nematodes, Steinernema riobrave, Heterorhabditis bacteriophora, and H. indica, were ev aluated as biopesticides against larvae of Diaprepes abbreviatus in a matur e citrus grove using different soil sampling methods, In three separate tes ts, commercial formulations of different nematode species were applied with herbicide delivery equipment at rates from 11 to 216 infective juveniles ( IJs)/cm(2) to the soil beneath the tree. The prevalence of parasitism and/o r predation by either commercially applied nematodes or indigenous natural enemies associated with weevil larvae in the soil was measured using larvae -baited screened cages placed in the soil before and after nematode applica tion. The results showed that ant predation and nematode parasitism were th e dominant mortality factors of caged, 6th instar D. abbreviatus during 7 d ays exposure to field soil, Entomopathogenic fungi and bacteria were incide ntal. Inundative applications of different rates of entomopathogenic nemato des showed a positive quadratic relationship between number of nematodes ap plied per given area (log scale) and parasitism of caged larvae. Higher rat es (>54 IJs/cm(2)) were required to achieve levels of parasitism significan tly greater than that in the controls. Nematode parasitism of D. abbreviatu s larvae was similar in caged versus no-cage comparisons conducted in the g reenhouse, Nematode numbers in the soil declined over time, reaching pretre atment levels at 14 days posttreatment based on a modified Baermann samplin g procedure, (C) 2000 Academic Press.