Bean alpha-amylase inhibitor 1 in transgenic peas (Pisum sativum) providescomplete protection from pea weevil (Bruchus pisorum) under field conditions

Two alpha-amylase inhibitors. called alpha Al-1 and alpha Al-2, that share 78% amino acid sequence identity and have a differential specificity toward mammalian and insect alpha-amylases are present in different accessions of the common bean (Phaseolus vulgaris). Using greenhouse-grown transgenic pe as (Pisum sativum), we have shown previously that expression of alpha Al-1 in pea seeds can provide complete protection against the pea weevil (Bruchu s pisorum). Here. we report that alpha Al-1 also protects peas from the wee vil under field conditions. The high degree of protection is explained by o ur finding that alpha Al-1 inhibits pea bruchid alpha-amylase by 80% over a broad pH range (pH 4.5-6.5). alpha Al-2, on the other hand. is a much less effective inhibitor of pea bruchid alpha-amylase, inhibiting the enzyme by only 40%, and only in the pH 4.0-4.5 range. Nevertheless, this inhibitor w as still partially effective in protecting field-grown transgenic peas agai nst pea weevils. The primary effect of alpha Al-2 appeared to be a delay in the maturation of the larvae. This contrasts with the effect of alpha Al-1 , which results in larval mortality at the first or second instar. These re sults are discussed in relationship to the use of amylase inhibitors with d ifferent specificities to bring about protection of crops from their insect pests or to decrease insect pest populations below the economic injury lev el.