Résumé
The relationship between plants and insects is generally considered from a Manichean point of view. So, phytophagous insects are separated from pollinating insects. The seeds of many Leguminosae (Fabaceae) are consumed by larvae of specialist Coleoptera (Bruchidae) which are considered pests of these plants. But some data show that adults visit the flowers before ovipositing on (or inside) the pods. The mature seeds of many Lathyrus spp. are consumed by larvae of Bruchus affinis. The flowers of some populations of L. latifolius, L. sylvestris and L. tuberosus are frequently visited by the adults of this insect whose mouth parts become abundantly contaminated with pollen. Such contaminated adults are not discovered on flowers of other species. In addition, though Fabaceae are essentially autogamous, the frequency of aborted flowers is very high in these three species. For these reasons: the specificity of the adult Bruchus-Lathyrus relationship, and the variability of abortion of their ovules, we suggest that the pollination activity of Bruchus affinis balances for these perennial plants the negative effect of the reduction of mature seeds by the larvae. The selective pressure of this destruction is debatable in perennial plants where propagation occurs by vegetative hypogeal parts. This is probably an example of the ambiguous nature of the relation between plants and insects.