Potentiation of B. Thuringiensis against S. Littoralis as Affected by Its Host Plants

Second instar larvae of the cotton leaf worm Spodoptera littoralis (Boisd.) showed obvious differences in their susceptibility to Bacillus thuringiensis when fed on treated foliage of different host plants. Rapid growth on lettuce plant allowed the larvae to tolerate more doses of the pathogen by developing into more resistant stages. On the other hand, plants which do not support full growth as onions and cabbage, showed a great stress on the insect. Slower rate of insect development caused its exposure for long periods to the impact of the disease. The feeding behavior of young larvae on different host plants was also considered as factors influencing the efficacy of B. thuringiensis.