Suspensions containing 0.25 and 1.25 g/liter of Bacillus thuringiensis subsp. israelensis (Bti) spore–toxin complex were spray-dried by using maltodextrin DE-6, corn starch, and nixtamalized corn flour (25 g/liter) as materials to entrap active δ-endotoxin. The inlet air temperature of the drier was kept constant at 141°C and the outlet temperature was maintained at 60 or 70°C. The Probit analysis of the concentration–mortality response of third instars of Aedes aegypti (L.) larvae of the spray-dried products at 60°C showed that LC50 values for maltodextrin DE-6 with 1 and 5% spore–toxin complex were 4 and 10% higher in toxicity, respectively, than that for the unformulated spore–toxin complex without drying. The LC50 value for corn starch with 1 and 5% of spore–toxin complex were also higher in toxicity (7 and 8% respectively). However, LC50 values for nixtamalized corn flour with one and 5% spore–toxin complex were 81 and 55% higher in toxicity, respectively. Dried products contain an aw ≤ 0.7, suggesting that they are able to keep the products without microorganism growth for longer periods. The scanning electron microscope of Bti spray-dried formulations with nixtamalized corn flour showed smooth spherical particles entrapping the active ingredient. These results suggested that Bti spore–toxin complex formulated with maltodextrin DE-6, corn flour, and nixtamalized corn flour, and then spray-dried may increase larval feeding and thus increase activity against Ae. aegypti larvae.
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Vol. 98 • No. 5