Integration of Entomopathogenic Nematodes and Fungi for Controlling the Cotton Leaf Worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae)

Pathogenicity ofthe two entomopathogenic nematodes (Heterorhabditis bacteriophora Poinar (HP88 strain) and Steinernema riobrave) and the two fungi (Metarhizium anisopliae and Beauveria bassiana) and their combinations were studied against the 3rd instar larvae of the cotton leaf worm Spodoptera littralis (Boisd.). LC50 values of bacteriophora were the most potent after 96 and 120 h of treatment, reached 568.6 IJs/ ml and 313.6 IJs/ ml, with a toxicity index (Ti=100& 100), respectively. Meanwhile, at 96 and 120 h post inoculation, LC50 values of S. riobrave were 701.9 IJs/ ml and 353.1 IJs/ ml with a toxicity index (Ti=56.74 and 88.81), respectively. Seven days post treatment, LC50 of M. anisopliae reached 2.897 Ex 10(8) conidia ml(-1) with a toxicity index (Ti = 100). On the other hand, B. bassiana LC50 value was 7.839 Ex 10(11) spores ml(-1) with a toxicity index (Ti = 36.96). Based on the co-toxicity factors; H. bacteriophora in combination with B. bassiana exerted an additional action with a co-toxicity factor (9.5).Also, the combination of S. riobrave with M. anisopliae gave an additional action based on a co-toxicity factor(-2.2), at 96h post treatment. Results indicated that the tested two bio-agents had variable mode of actions and resulted to insignificantly effects with additive actions.Observed mortality caused by both tested bio-agents was higher as compared to the use of each agent singly.