Some factors affecting the activity and pathogenicity of heterorhabditis heliothidis and steinernema carpocapsae nematodes

ABSTRACT

The activity of Heterorhabditis heliothidis, Steinernema carpocapsae 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 Indicated that the activity and pathogenicity of H. heliothidis and S. carpocapsae infective juveniles of entompathogenic 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. carpocapsae are more active and quicker in killing insects in the soil of the pH value above 6.9 and 8 than 5.6. In 15C, only H. heliothidis caused the host mortality. In 20C and 25C, both nematodes showed high activity. There was no significant difference in the effect of 20C on the activity of both H. heliothidis and S. carpocapsae; but in the temperature of 25C, 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