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.

Comparative studies on the production of invasive larvae of Steinernema feltiae Filipjev nematodes within insect host.

A comparative study has been made on the production of invasive larvae of Steinernema feltiae Filipjev within the cotton leafworm Spodoptera littoralis Boisduval and house fly Musca domestica Linnaeus. The results indicated that there is a positive correlation between the reproductive rate of invasive larvae and the initial dosages, host species and host stages. The reproductive rate of invasive larvae of Steinernema feltiae in Spodoptera littoralis imagos and caterpillars was higher than in M. domestica. At the pupal stages of M. domestica, no reproduction was obtained. Pupae were refractory to parasitism presumably owing to the effective protection afforded by the puparium. S. feltiae would be better adopted to live in S. littoralis than in M. domestica.

Steinernema parasitism of larvae of the house fly Musca domestica Linneous.

The histopathological effect of different dosages 50, 100, 200, 500 and 1000 of Steinernema feltiae Filipjev larvae on the larval tissues of Musca domestica Linneous has been studied. It was found that S. feltiae nematodes invade the fat tissue, gut, cuticle and muscle tissue of the host. All of these tissues, along with the gut epithelium, show signs of disintegration before death of the host. The tissue of the gut and the fat body are the most severely damaged by the presence of S. feltae. The destructive damages described in this investigation depend mainly upon the time and the intensity of infection.

Comparative studies on the development of the entomogenous nematodes Steinernema feltiae Filipjev on Spodoptera littoralis (Boisduval) and Musca domestica Linneous.

Comparative studies were made at 26 degrees C under laboratory conditions on the development of Steinernema feltiae Filipjev (= Neoaplectana carpocapsae) on the different stages of Spodoptera littoralis (Biosduval) and Musca domestica (Linneous). In the present investigation the host species influence manifested itself, in a quicker development rate along with the cotton leafworm S. littoralis. Particular development stages took place earlier in the S. littoralis than in M. domestica. As far as the occurrence dates of particular stages of S. feltiae were concerned, the differences in relation to the two host species were significant. The changes in numbers of giant forms in the development course of populations in the caterpillars, pupae and imagos body of both species were studied. The numbers of giant forms correspond with the numbers of invasive larvae, it seems that at first they are growing and then decreasing.

The influence of infection with Steinernema feltiae Filipjev on the haemocyte picture of the cotton leaf worm (Spodoptera littoralis Boisduval).

Infection of Spodoptera littoralis Boisduval larvae with Steinernema feltiae Filipjev nematodes caused sharp variation in proportional percentages of differential haemocyte counts. The mean total haemocyte count per mm3 of haemolymph in control larae of S. littoralis was 6000 haemocyte mm3. After infection with 50, 100, 200 and 500 parasitic nematodes of S. feltiae, the mean total count was significantly increased to 17,250, 18,600, 21,000 and 24,000 haemocyte mm3 respectively.