Efficacy of the entomopathogenic nematode Heterorhabditis bacteriophora using different application methods in the presence or absence of a natural enemy

Various application methods for the entomopathogenic nematode Heterorhabditis bacteriophora were evaluated under laboratory and field conditions. Four different methods of applying the infective juveniles (IJs) of the nematode to soil were assessed including (1) insect cadavers (referred to as nematode- infected cadavers), (2) subsurface injection, (3) spraying, and (4) drip irrigation. In the laboratory experiment, except for the control with no nematodes, all treatments showed more than 95% insect mortality of the bait insect (Galleria mellonella) with no significant differences among treatments. The same experimental setup was conducted with the introduction of mites, Sancassania polyphyllae (Acari: Acaridae), which are natural enemies of entomopathogenic nematodes. The treatment groups with mites and the control group without mites showed more than 87% insect mortality and no significant differences were observed. The nematode- infected cadaver application method was further evaluated by using cadavers of different ages containing H. bacteriophora IJs in the presence of mites. Larval mortality of the bait insect was significantly lower when 3- or 6- dayold nematode- insect cadavers were used in the presence of mites. Different application methods were also tested in a corn field. No significant differences were observed among the application methods. Our results indicate that the different application methods had no significant effect on larval mortality, but the presence of mites had a negative effect on the cadaver application when the cadavers were 3 days old but had no significant effect when the cadavers were 6 and 9 days old.