Abstract
The aim of this study was to induce recombinants in Bacillus thuringiensis species that are toxic to pests in the environment of Saudi Arabia. The lab performance of certain released Bt treated Ricinus communis for their effect on Spodoptera litura were evaluated in comparison with non Bt plant parts. Two Bacillus strains were used in this study belonging to Bacillus thuringiensis and Bacillus subtilis. These strains were genetically marked using antibiotics and crystal violet. The strains were conjugated depending on the opposite genetic markers. From the mating four recombinant transconjugants were isolated to be evaluated for insecticidal activity against the larvae of Spodoptera litura. Investigations of toxicological studies were therefore carried out to evaluate the potential role of Bacillus thuringiensis (Bt) recombinants as a natural pest control agent against Spodoptera litura. Two different formulations of the recombinant pathogens were tested for their efficacy against the pest. The results appeared that larvae feeding on Bt treated plants was weight decreased than non Bt treatment in control experiment. It can be concluded that Bacillus thuringiensis has a great potential for controlling and suppress the feeding of larvae on plant leaves. It is interesting to note that mortality, developmental rates and larval body weights were greater on the diet containing crystals + endospores than that in the diet treated with crystals. Average weight of larvae tolerated Bt intoxication appeared more weight increase than that in non Bt feeding. In addition, increased general average weight achieved that larval weight was increased in Bt sprayed plants with crystals + endospores than that in Bt sprayed with crystals alone. Accumulated larval mortality was increased in response to diet treated with crystals and endospores than that treated with crystals. This indicated that the diet treated with Bt containing crystals and endospores was more toxic than that containing crystals only. However, the ratio between consumption to the weight of surviving larvae was slower in all Bt treatment diet than that in non Bt treatment diet. while, the average of consumed diet treated with crystals + endospores was slower than that treated with crystals. On the other hand, the ratio between feed consumption to the weight of surviving larvae was greater in the diet treated with crystals + endospores than that treated with crystals. This indicated that larvae tolerated high toxic agents (crystals + endospores) was highly efficient in metabolism of diet to overcome diet toxic effects. These results indicated that there is a dire need to search and test more and more recombinant isolates of Bt for tracing out the best to achieve maximum control of cotton and vegetables leaf worm to reduce pesticides needed, because of historically, resistance to insecticides which has been a limiting factor for effective chemical control of cotton and vegetables pests in the world