Evaluation of two nematode strains against the Egyptian cotton leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) in the laboratory

Efficacy of the two nematode strains; Steinernema riobravae and Heterorhabditis sp. (ISK-2) (Egyptian isolates) on the fourth larval instars of the Egyptian Cotton le leaf worm, Spodopter littoralis (Boisd.) (Lepidoptera: Noctuidae) was studied under laboratory conditions. D ita indicated that S. riobravae was more effective than Heterorhabtidies sp. (ISK2) and the concentration of 75 IJs/l gave highest mortality percentages compared with the other concentrations tested. The infectivity of S. riobravae it the concentration of 15 IJs/l was tested against the prepupae, pupa and the adult stages of S. littoralis. Data indicated that the pupae were less susceptible to nematodes' infection in soil than prepupae and adults. Mortality of pupae exposed to nematode was decreased from 38 to 29% by increasing the exposure time from 3 to 7 days after the prepupae browning into the soil. In addition, there was a malformation of adults emerged treated pupae. Adults of S. littoralis were susceptible to nematodes' infection is they emerged from the soil. The majority of nematode induced mortality within 24 hr after emergence many abnormal adults were observed; they could not mate or lay eggs. Data indicated also that, the appropriate stage for controlling S. littoralis by S. riopravae nematode is the prepupa, where 73-93% of the population was killed.