Abstract

Cucurbitacin-containing phytonematicides have potent nematicidal effects on plant-parasitic nematodes, but their effects on entomopathogenic nematodes (EPN) are unknown. The objective of our study was to determine the effects of cucurbitacin-containing Nemafric-BL phytonematicide on the viability (survival and mortality) of the EPN Steinernema feltiae. Infective juveniles (IJ) of S. feltiae were exposed to dilutions of the phytonematicide at 0.0, 1.5, 3.0, 4.5, 6.0, 7.5 and 9.0% for 24, 48 and 72 h. Survival and mortality of IJ over increasing concentrations of the test phytonematicide exhibited negative and positive quadratic relations, respectively. Since y-intercepts in mortality curves were higher than zero, observations were adjusted for corrected mortality and subjected to lines of the best fit. Corrected IJ mortality over increasing phytonematicide concentrations exhibited positive quadratic relations, with y-intercept being equivalent to zero. Infective juvenile survival and corrected mortality over increasing Nemafric-BL phytonematicide concentrations exhibited quadratic relations, with survival relations explained by 93, 93 and 90% COD at 24, 48 and 72 h exposure durations, respectively. The optimum concentration for corrected IJ mortality and minimum concentration for IJ survival were almost equivalent. In conclusion, within the tested concentration ranges, the sensitivity of S. feltiae IJ to the phytonematicides was low as shown by the gradual increase in corrected IJ mortality and the gradual decrease in IJ survival, without intersection of the two curves.