VIRULENCE OF THE NEMATODE (STEINERNEMATIDS AND HETERORHABDITIS) BACTERIA (XENORHABDUS SPP.) COMPLEX TO THE EGYPTIAN COTTON LEAFWORM SPODOPTERA-LITTORALIS (LEPIDOPTERA, NOCTUIDAE)

The differences in pathogenicity of five entomoparasitic nematodes of the families Steinernematidae and Heterorhabditidae to fourth instar larvae of the Egyptian cotton leafworm Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae) were determined under laboratory conditions. The "IS" strain of Heterorhabditis was the most pathogenic and S. glasseri was the least. The rate of nematode invasion into the insect was proportional to the overall pathogenic effect of the various nematodes. No significant differences were recorded in the rate of insect mortality when surface-sterilized infective juvenile from the various strains were directly injected to the hemolymph. The highest rate of insect mortality due to injection of the symbiotic bacteria, isolated from the various nematodes, was achieved by the H. bacteriophora "HP88" strain. The lowest mortality rate following bacterial injection was recorded with Heterorhabditis sp. "IS" and S. glaseri. © 1991.