CONTROL OF CYLAS FORMICARIUS USING ENTOMOPATHOGENIC NEMATODES ISOLATED FROM HAWAIʻI

Entomopathogenic nematodes (EPN) have potential to control the sweetpotato weevil (SPW; Cylas formicarius). Laboratory tests were conducted using Steinernema feltiae MG-14, Oscheius tipulae OA-12, and Heterorhabditis indica OM-160 isolated from Hawaiʻi on larvae of SPW in infection courts. Subsequently, S. feltiae was tested for effectiveness at 0.5, 1.0, and 2.5 billion infective juveniles (IJ)/ha in a sweetpotato field. In another field experiment, monthly applications of O. tipulae were evaluated for SPW control. In the laboratory assays, S. feltiae, O. tipulae, and H. indica caused an adjusted mortality (mortality of treatment – mortality in control) of 50%, 30%, and 25% to SPW larvae, respectively. In a field experiment with S. feltiae, SPW damage and SPW densities were low (< 1 SPW/kg sweetpotato swollen root) across all application rates, resulting in an inconclusive study. In contrast, the field experiment testing O. tipulae experienced high SPW pressure (32 SPW/kg root in the untreated control). Sweetpotato treated with O. tipulae suffered less damage and had lower SPW densities than the nontreated control (P ≤ 0.05). In conclusion, all three EPN species isolated from Hawaiʻi showed promise in suppressing SPW in the laboratory and in the field.