Toxic effect of Canavalia ensiformis seed coat on larval development of Callosobruchus maculatus

Abstract

The outer-covering of seeds is known as the seed coat, and this is the seed's first protective barrier against the penetration of insects. In this sense, seed coat toxicity can affect insect development. In this work, we study the influence of the Canavalia ensiformis seed coat on embryonic and larval development of Callosobruchus maculatus. Oviposition of C. maculatus was negatively affected by the seed coat, while embryonic development occurred without any morphological or biochemical alterations. During larval development, physiological changes comprising delay in body weight, the inability of larvae to penetrate the C. ensiformis seed coat, and decreases in biochemical parameters, such as contents of glucose, proteins, and triglycerides, were recorded. Although larvae survived until 17 days after oviposition, they could not penetrate the C. ensiformis seed coat. A dose-dependent effect was observed on female oviposition, mass, and survival of larvae of C. maculatus. Cysteine protease, α-amylase and α-glucosidase activities decreased while aspartic protease activity increased with increases in ingestion of seed coat flour. Larval post-embryonic development was affected by C. ensiformis seed and this interference is related with a toxic seed coat which reduced activities of several key digestive enzymes, resulting in severe weight loss.