Compatibility of transgenic legumes and parasitoids to control bruchids (Coleoptera: Chrysomelidae)

Bruchid beetles (Coleoptera: Chrysomelidae) are important pests of stored legume seeds. Chickpea and cowpea plants have been transformed to express the α-amylase inhibitor αAI-1 from the common bean. These plants are highly resistant to many important bruchid species, including Callosobruchus spp. Other species such as Acanthoscelides obtectus and Zabrotes subfasciatus are not affected by αAI-1.

A powerful approach to control also such tolerant species might be the combination of αAI-1 transgenic seeds with hymenopteran parasitoids.

To assess the impact of αAI-transgenic legumes to bruchid parasitoids, we have thus assessed (i) whether bruchid parasitoids rely on α-amylases for carbohydrate digestion and whether their α-amylases are inhibited by αAI-1; (ii) whether parasitoids ingest harmful amounts of the inhibitor, (iii) whether parasitoids are adversely affected when feeding on larvae of αAI-1 tolerant bruchids developing in αAI-1 transgenic seeds.

Our results for five parasitoid species from 3 families indicate that both females and larvae possess α-amylase activity and thus appear to rely on α-amylases for carbohydrate digestion. In vitro inhibition studies have confirmed that α-amylases of both larvae and females of all parasitic wasps were strongly inhibited by αAI-1. We could, however, not detect an adverse effect on the parasitoid Dinarmus basalis when attacking larvae of the αAI-1 tolerant bruchid Z. subfasciatus developing in αAI-1 transgenic cowpea seeds. This appears to be due to the low level of exposure to the insecticidal factor.

Thus, αAI-1-transgenic legumes appear to be compatible with parasitoids to control bruchid pests.