Susceptibilidad de cuatro nóctuidos plaga (Lepidoptera) al gene Cry1Ac del Bacillus thuringiensis incorporado al algodonero

Abstract

Transgenic plants possessing genes of the bacteria Bacillus thuringiensis (Bt) which codify for toxin production effective against some pests, are considered useful within the management of insects. However, these commercial cultivars do not control satisfactorily all noctuids, and besides, at a distance, induce resistance. Diverse populations of native Heliothis virescens, Helicoverpa zea, Spodoptera frugiperda and S. sunia strains were evaluated to determine the susceptibility to the toxin Cry1Ac of the cultivar Bollgard®, planted in Colombia. Cry1Ac was obtained from a Bt gene cloned in Escherichia coli and from MVP® (protoxin encapsulated in Pseudomonas). Neonate larvae were exposed to seriated dose of the toxin, incorporated within meridic diet and also fed with fresh transgenic cotton tissue. Weight and adult emergency of the survivors were determined. Results were submitted to an Anova and LC was obtained by Probit analysis. An acceptable susceptibility of H. virescens, LC 50 of 3.52 and 3.81 μg/mL, 2005A y 2006A, respectively, and a 100% mortality when feeding neonates with terminal leaves was found. LC 50 for H. zea varied from 3.42 to 6.12 μg/mL; as the toxin dose increased, the pupal weight decreased and a high percentage of deformed pupae were observed. For Spodoptera spp., LC 50 oscilated between 192 y 1.178 μg/mL, showing its resistance to the toxin. It was concluded that, at the moment, the transgenic cotton provides satisfactory control of the Heliothine, but no of the Spodoptera complex.