A LABORATORY STUDY OF SUSCEPTIBILITY OF HELICOVERPA ARMIGERA (HUBNER) TO THREE SPECIES OF ENTOMOPATHOGENIC NEMATODES

The insecticidal effect of Heterorhabditis bacteriophora Poinar (Rhabditida: Nematoda: Heterorhabditidae), Steinernema carpocapsae (Weiser) and Steinernema feltiae (Filipjev) (Rhabditida: Nematoda: Steinernematidae), was examined against Helicoverpa armigera under laboratory conditions. The nematodes were used in the following doses: 0 (control), 1, 10, 50, 100 and 500 infective juveniles (IJs) per insect, and their infectivity was tested at 22° C after 72, 96 and 120 h. of exposure using three methods of filter paper assay, food assay and soil assay. In all trials, H. bacteriophora IRA10 had the highest toxicity and S. carpocapsae IRA18 the lowest. There were no significant differences between strains at the lowest concentration in all exposure times. In filter paper assay, a dose of 500IJ/Larvae of H. bacteriophora IRA10 after 120h of exposure time caused 83% mortality, whereas S. feltiae IRA24 and S. carpocapsae IRA18 caused 71.67%and 30% mortality, respectively. In food and soil assay, similar results were found and H. bacteriophora IRA10 was more pathogenic against cotton bollworm compared to S. feltiae and S. carpocapsae.