Revista Brasileira de Milho e Sorgo (Aug 2004)
BIOLOGICAL ACTIVITY OF BT TOXINS, CRY 1A(b) AND CRY 1F ON Spodoptera frugiperda (SMITH) (LEPIDOPTERA: NOCTUIDAE)
Abstract
There are currently two different toxins from Bacillus thuringiensis (Bt) available in transgenic maize. However, there is limited information regarding the toxicity of purified Cry 1Ab and Cry1F toxins to fall armyworm (FAW), Spodoptera frugiperda (Smith), using a surface exposure method with artificial diet. Bioassays were conducted using a range of concentrations for both toxins. Each treatment was artificially infested with neonate FAW larvae and maintained under constant temperature and complete darkness. Ten days after exposure, the number of surviving larvae and growth inhibition based on biomass were evaluated. The mortality data were subject to Probit analysis. The estimated LC50’s for Cry1Ab and Cry1F were, respective 689.81 ng/cm2 and 36.46 ng/cm2. The LC50 was enough to inhibit the biomass accumulation of larvae by 91.61% and 89.81% for Cry1Ab and Cry1F, respectively. The larvae that survived after 10 days on Cry1Ab treated diet were transferred to untreated diet and observed until adult emergence. Out of the surviving larvae, 62.8% recovered their development reaching the normal pupa biomass. Therefore, the biological activity of Bt toxin extends beyond toxicity including a significant feeding inhibition. This fact has significant implications for the development of resistance management strategies.
