Biopesticide formulated products contain the active material and other components, which are involved in the final performance of the product. The study of the interactions among the different components in the final product can provide us with clues about which elements interact with in an additive, synergistic or antagonistic way. The commercial products based on B. thuringiensis as the active ingredient contain a mixture of crystals and spores obtained as an end product of the fermentation process. However, it is worth to note that Bt, when it infects the larva, can produce other insecticidal compounds during the vegetative phase of growth. We are also studying the way to incorporate these compounds into the final product.

Regarding the Cry proteins, which are the main compounds contributing to the insecticidal potency of Bt-based insecticides, nowadays there is none of commercial Bt product which describes the content and proportion of Cry proteins in the formulation. This description would be of great value to predict the toxicity spectrum and the relative potency against many insect pests for which their susceptibility to the individual Cry proteins have been reported. We are developing analytical techniques to determine this composition and to provide information on which bacterial strains with complementary activities would be wise to combine. Additional studies about synergistic and antagonistic effects are being carried out.

Other components of the formulation can potentiate the toxicity, i.e. the spore. We are particularly interested in the BtBs proteins (from insects) that have been described to synergize Cry proteins and from which a product has already been registered in the USA. These kind of proteins can be added to Bt formulations or expressed in transgenic crops along with cry genes.

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