Effect of Host Age and Nematode Strain on Susceptibility of Spodoptera frugiperda to Steinernema feltiae
AbstractMedian lethal concentrations (LC[sub5][sub0]) 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[sub5][sub0] 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[sub5][sub0] 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. Key words: entomogenous nematode, median lethal concentration, Neoaplectana, Steinernema bibionis, Steinernema feltiae, virulence.
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