Life-cycles and Competition-avoiding Strategies of Seed-eating Weevil Species on Broom Species (Coleoptera: Curculionidae / Leguminosae: Genisteae)

Abstract

In the centre of the Iberian Peninsula, 5 species of seed-eating weevils show different degrees of host specificity inhabiting species of the broom genera Cytisus Linnaeus and Genista (Tournfourt) Almost all of them are confined to one or 2 closely related host species. There are (a) monophagous species: Exapion laufferi (Schilsky 1906), restricted to Genista cinerascens Lange; (b) oligophagous species restricted to one genus: E fuscirostre (Fabricius 1775) to the genus Cytisus, and E putoni (Ch Brisout 1866) to the genus Genista; (c) oligophagous species in a broad sense: E compactum (Desbrochers 1888) and Pachytychius sparsutus (Olivier 1807) exploiting several species of both genera. Species of the broom genera Adenocarpus De Candolle and Retama Rafinesque were not found to be inhabited by seed-eating weevils, perhaps because of the chemical and morphological characteristics of their pods. In accordance with their degree of specialization, there is a close synchrony between the life cycles of the various weevil species and the phenology of their host plants: The weevils reached peak numbers when the respective main food source for their larvae was available, i.e, when the specific host plants began pod formation. The specialization of these weevil species, such as differences in their oviposition sites, ways of entering the seeds as well as the larval feeding positions inside the seed, are strategies to avoid competitors, to foster coexistence, and to enable the optimal explotation of the resource.