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Infestations of stored legume seeds by bruchid beetles, such as the cowpea weevil and the Azuki bean weevil cause substantial economic and nutritional losses of these food crops, especially in developing countries. Seeds of the common bean are resistant to these bruchids largely because of the presence of α-amylase inhibitor (αAI-Pv), a seed protein that is toxic to the larvae. The αAI-Pv gene is therefore a candidate for a genetic engineering approach that would make other legumes (pea, chickpea, cowpea, Azuki bean) resistant to bruchid infestations. We tested this possibility by transforming peas (Pisum sativum) with the αAI-Pv gene driven by a strong seed-specific promoter. The levels of αAI protein in the pea seeds were as high as in bean seeds and the peas were resistant to the cowpea and Azuki bean weevils.

Genetic engineering may be used to introduce multiple insect resistance genes with different modes of action into crop plants. We explored the possible interactions of two differing gene products fed in the diet of cowpea weevil, Callosobruchus maculates (F.), a stored grain pest. The soybean cysteine protease inhibitor soyacystatin N (scN) and α-amylase inhibitor (αAI) from wheat have defensive function against this coleopteran. When artificial seeds containing both scN and α(AI) were infested with eggs of C. maculatus, the delays in larval development were longer than was predicted by summing the developmental delays seen when larvae were fed a diet containing the individual proteins, indicating that the effects of scN and α(AI) are synergistic. α(AI) was readily hydrolyzed when incubated with insect gut extract. This proteolytic degradation was inhibited by scN, but not by Kunitz inhibitor (a serine protease inhibitor). Thus, degradation of α(AI) was due to proteolysis by insect digestive cysteine proteases. These data suggest that C. maculatus uses digestive enzymes not only to function in food protein digestion but also to defend the insects themselves by helping reduce the concentration of a toxic dietary protein.

The study of the cereal leaf beetle, Oulema melanopus (L.), (Coleoptera: Chrysomelidae) was conducted in 1966 in 2 oat fields with different population densities in Indiana. The average number of eggs deposited per linear foot of row was 194 in the high-density field and 59 in the low-density field. All the eggs used to assess egg mortality in both study groups were 1 day old on May 20, when the study was begun. In the low-density field egg mortality from all causes was 60.3%. Predation by adults of the lady beetle Coleomegilla maculata (De Geer) and the convergent lady beetle, Hippodamia convergens Guérin-Méneville, was the primary biological factor causing egg mortality. The adults and larvae of these 2 coccinellids were also the primary biological agents responsible for larval mortality. Larval mortality from all causes was 72%. Prepupalpupal mortality was 42%. A total mortality of 93.8%, from day-old eggs to newly emerged adults, occurred in the low-density field Adults of the same 2 species of coccinellids were also the primary biological agents responsible for egg mortality in the high-density field. Egg mortality from all causes was 52.2%. Adults and larvae of these 2 coccinellids were the primary biological agents responsible for larval mortality, while rainstorm activity was the major physical factor. Larval mortality from all causes was 58.5%. Prepupal-pupal mortality was 54.5%. The total mortality in the high-density field, from day-old eggs to newly emerged adults, was 91.2%. Additional observations showed that larval mortality late in the season occurred when larval feeding depleted the food supply. Larval mortality caused by rainstorm activity in the high-density field following each of 2 rainstorms was 14.5 and 13.5%, respectively. Mortality of newly emerged adults in the high-density field ran as high as 2.8 per linear foot of row. This mortality was attributed to larval competition for a limited food supply prior to pupation, effects of high soil temperatures and low soil moisture during the pupal period, and lack of an immediate source of food and moisture for the adults upon emergence from pupae.