RESUMO
Median lethal concentrations (LC) were determined for four nematode populations (two strains of Steinernema feltiae, a S. feltiae hybrid, and S. bibionis) against fifth-instar fall armyworm (Spodoptera frugiperda) larvae and for the most virulent of these nematodes against different instars and stages of the insect. Based on lack of overlap of 95% fiducial limits, there were significant differences in virulence among the four nematodes. The LC ranged from 7.6 to 33.3 nematodes/ 0.7 ml water, and slopes of the log dose-probit regression lines were similar except for the S. feltiae All strain. First-instar fall armyworms suffered virtually 100% mortality from the S. feltiae Mexican strain at 1.0 nematode/0.7 ml, and LC were 2.3 and 7.9 nematodes/0.7 ml in third-instar and fifth-instar larvae, respectively. Pupae had 7-20% mortality at doses ranging from 30 to 60 nematodes/0.7 ml.
