Hardness of some fabaceous seed coats in relation to larval penetration by Acanthoscelides obtectus (Say) (Coleoptera: Bruchidae)

A simple device is described for the measurement of seed coat hardness of Phaseolus vulgaris L., Phaseolus lunatus L., Phaseolus coccineus L., and Lablab purpureus L. The ability of Acanthoscelides obtectus (Say) larvae to penetrate P. vulgaris seeds is strongly affected by seed coat hardness. Comparisons between the four species suggest differences in the chemical properties of the seed coat of P. lunatus seeds. Some hypotheses are suggested for the relationship between A. obtectus larvae and their host plant.