Effect of a trypsin inhibitor from Dimorphandra mollis seeds on the development of Callosobruchus maculatus

Bruchid larvae cause major losses in grain legume crops throughout the world. Some bruchid species, such as the cowpea weevil, are pests that damage stored seeds. Plants synthesize a variety of molecules, including proteinaceous proteinase inhibitors, to defend themselves against attack by insects. In this work, a trypsin inhibitor (DMTI-II) isolated from Dimorphandra mollis seeds was tested for anti-insect activity against Callosobruchus maculatus larvae. The inhibitor produced ca. 67% mortality to this bruchid when incorporated into an artificial diet at a level of 1%. The doses necessary to cause 50% mortality (LD₅₀) and to reduce weight by 50% (ED₅₀) for DMTI-II were ca. 0.50% and 0.60%, respectively. The action of DMTI-II on C. maculatus larvae may involve the inhibition of trypsin-like activity of larval midgut extracts, the absence of digestion by midgut preparations or with a mixture of pepsin and papain, and its association with a chitin column and chitinous structure in the midgut of this insect.