Synergism and antagonism between Bacillus thuringiensis Vip3A and Cry1 proteins in Heliothis virescens, Diatraea saccharalis and Spodoptera frugiperda

Synergism and antagonism between Bacillus thuringiensis Vip3A and Cry1 proteins in Heliothis virescens, Diatraea saccharalis and Spodoptera frugiperda

Second generation Bt crops (insect resistant crops carrying Bacillus thuringiensis genes) combine more than one gene coding for insecticidal proteins in the same plant to provide a better control of agricultural pests. Some of the new combinations involve co-expression of cry and vip genes. Since Cry and Vip proteins have different midgut targets and possibly different mechanisms of toxicity, it is important to evaluate possible synergistic or antagonistic interactions between these two classes of toxins. Three members of the Cry1 class and three from the Vip3A class were tested against Heliothis virescens for possible interactions. At the level of LC₅₀, Cry1Ac was the most active protein, whereas the rest of proteins were similarly active. However, at the level of LC₉₀, Cry1Aa and Cry1Ca were the least active proteins, and Cry1Ac and Vip3A proteins were not significantly different. In the experimental conditions used, we found an antagonistic effect of Cry1Ca with the three Vip3A proteins and a slight antagonism of Vip3Af with either Cry1Aa or Cry1Ac. The interaction between Cry1Ca and Vip3Aa was also tested on two other lepidopterans. Whereas antagonism was observed in Spodoptera frugiperda, synergism was found in Diatraea saccharalis. In all cases, the interaction between Vip3A and Cry1 proteins was more evident at the LC₉₀ than at the LC₅₀ level. The fact that the same combination of proteins may result in a synergistic or an antagonistic interaction may be an indication of different types of interaction with the host depending on the insect species tested.