Development of Callosobruchus chinensis (L.) and C. maculatus (F.) (Coleoptera: Bruchidae) in seeds of Vicia faba L. Differing in their tannin, vicine and convicine contents

The seeds of the tested genotypes of Vicia faba L. differed by the presence or absence of tannins in the seed coat and in the level of vicine and convicine in the cotyledons. In vertebrates, these two glycosides can be transformed into divicine and isouramil which influence the enzymatic activity of glucose-6-phosphate dehydrogenase (G-6-PDH). Callosobruchus chinensis (L.) develops in V. faba seeds and causes high losses during storage. C. maculatus (F.) is less able to develop in the seeds of V. faba. For both bruchids the seed coat represents a barrier that only 45-60% of larvae overcome. The presence of tannins did not affect the perforation rate. The texture of the seed coat, its hardness or the presence of other toxic compounds could explain these results. The larvae of C. chinensis were able to develop in the seeds of V. faba whatever their vicine and convicine contents and the survival rate during the post-embryonic development was higher than 70%. The larvae of C. maculatus could only develop well in seeds poor in vicine and in convicine. The Ll larvae died as soon as they began to consume the cotyledons of the seeds containing high levels of glycosides. The presence of vicine in the seeds seemed to be the main mortality factor for C. maculatus larvae. Variations in the convicine content had a more limited influence. The enzymatic activity of G-6-PDH in haemolymph depended on the seed vicine and convicine contents and the bruchid species. This activity was low when larvae developed in seeds rich in vicine and covicine. Whatever the genotype of the seeds, the enzymatic activity of the G-6-PDH was always higher in C. chinensis adults than in C. maculatus adults. Varietal selection, through the reduction of the vicine and convicine content of the seeds, can favour the colonization of V. faba by other phytophagous insects such as C. maculatus.