Some factors affecting the activity and pathogenicity of Heterorhabditis heliothidis and Steinernema carpocapsae nematodes.

The activity of Heterorhabditis heliothidis (Khan etal) and Steinernema carpocapsae (Weiser) and pathogenicity of those nematodes in relation to cotton leafworm Spodoptera littoralis (Boisd) has been studied under certain factors (soil moisture, temperature, acidity and depth of soil). The results have indicated that the activity and pathogenicity of H. heliothidis and S. carpocapsae infective juveniles of entomopathogenic nematodes placed below the soil surface depend on factors mentioned before. It has been demonstrated that the free living stages of infective larvae of H. heliothidis and S. carpocasae are more active and quicker in killing of insects in the soil of the PH. value above 6.9 and 8.0 than 5.6. In 15 degrees C only H. heliothidis caused the host mortality. In 20 degrees C and 25 degrees C both nematodes showed high activity. There was no significant difference in the effect of 20 degrees C on the activity of both H. heliothidis and S. carpocapsae but in the temperature of 25 degrees C the activity of H. heliothidis was higher than that of S. carpocapsae. When cotton leafworm larvae are placed on the soil surface at different distances from the nematodes the shortening of those distances resulted in the shortening of the insect longevity and increasing the percentage of insect mortality.