Life-cycles and competition-avoiding strategies of seed-eating weevil species on broom species (Coleoptera : Curculionidae/Leguminosae : Genisteae)

In the centre of the Iberian Peninsula, 5 species of seed-eating weevils sh ow different degrees of host specificity inhabiting species of the broom ge nera Cytisus Linnaeus and Genista (Tournfourt). Almost all of them are conf ined to one or 2 closely related host species. There are (a) monophagous sp ecies: Exapion laufferi (Schilsky 1906), restricted to Genista cinerascens Lange; (b) oligophagous species restricted to one genus: E fuscirostre (Fab ricius 1775) to the genus Cytisus, and E putoni (Ch Brisout 1866) to the ge nus Genista; (c) oligophagous species in a broad sense: E compactum (Desbro chers 1888) and Pachytychius sparsutus (Olivier 1807) exploiting several sp ecies of both genera. Species of the broom genera Adenocarpus De Candolle a nd 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 phe nology of their host plants: The weevils reached peak numbers when the resp ective main food source for their larvae was available, i.e, when the speci fic host plants began pod formation. The specialization of these weevil spe cies, such as differences in their oviposition sites, ways of entering the seeds as well. as the larval feeding positions inside the seed, are strateg ies to avoid competitors, to foster coexistence, and to enable the optimal explotation of the resource.