The sweet potato ( Ipomea batatas L.) is an important food crop worldwide. In many countries where drought is a common occurrence, sweet potatoes are a staple and a basic security food crop. The most important bio-constraint is the sweet potato weevil ( Cylas spp.). Weevils cause losses in yield of between 60% and 100% and are worldwide problem. In the US, weevils are the most serious problem of sweet potato production in all the southern states and cause losses worth tens of millions of dollars and restrict marketing of the produce. Weevil larvae damage also imparts a characteristic furanoterpeonoid to roots rendering even slightly damaged roots unfit for human consumption. The aim of this study was to develop a semi artificial diet for use in toxin incorporation studies. Several Bacillus thuringienis (Bt) and Cholesterol Oxidase (ChoM) toxins were investigated for their efficacy in controlling sweet potato weevil larvae (Cylas formicarius (fabricius) and baseline data obtained. The results indicate that at 5ppm, Bt toxin ET70 and ET33/34 were the most effective and resulted in the highest larval mortality of 100% and 97% respectively after 15 days of feeding. Adding ChoM to Bt. Toxins in the diet was significantly synergistic and led to a higher larval mortality (day five) in the assay period. This data is important in predicting the toxicity effects on weevil larvae in sweet potato plants that are genetically engineered to express these toxins either alone or in combination.
Species 1: Bacillales Bacillaceae Bacillus thuringiensis
Species 3: Coleoptera Curculionidae Cylas formicarius
Keywords: sweet potato, larval mortality
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