How bean weevil (Acanthoscelides obtectus, Coleoptera, Bruchinae) larvae die on legume seeds

Abstract

Background The host specificity of the dry bean weevil, Acanthoscelides obtectus Say (Coleoptera: Bruchinae), a seed predator of beans, is not properly known. Occasional use of leguminous seeds other than beans is reported, however the sphere of possible wild and cultivated hosts is uncertain. Female oviposition preference and larval performance relationship is complicated by the respective importance of seed coat and cotyledon, because paradoxically, females must exercise oviposition preference on the basis of stimuli provided by the seed coat alone, without directly being able to assess the quality of cotyledon’s suitability for larval development.Results Host specificity and host range investigations carried out on seeds of 62 grown and naturally occurring legume species and 82 cultivars of Phaseolus, Pisum, Glycine, Lens and others in Hungary, using no-choice tests for egg-laying, and intact or pierced seed coat for larval development in seeds, showed that there were 18 plant species (35% of them Lathyrus) that supported larval development to adults, however, only nine species (4 of 17 Glycine max accessions, Vigna unguiculata, V. angularis, Phaseolus vulgaris, Ph. coccineus, Cicer arietinum, Vicia faba, Lathyrus sativus and 13 of 27 Pisum sativum accessions) allowed it if the seed coat was intact. Furthermore, there was no overall positive correlation between oviposition preference and larval performance, with the exception for the so-called acceptable non-hosts (Kendall’s τ = 0.3088). Bean weevil females also demonstrated an ovipositional hierarchy of legume species even in no-choice tests.Conclusions Host range expansion is not probable with the bean weevil, primarily because it would require the recognition of basically different oviposition substrates (pods) among outdoor conditions.