Bean weevil (Acanthoscelides obtectus (Say)) females were found to use seeds (discrete resource patches) differentially when different sizes were offered in multiple-choice tests. Females, either as a group or as individuals, laid significantly (two to six times) more eggs on large seeds than on those of five times smaller mass. In contrast, seed shape (flattened or spherical) did not contribute to clutch-size adjustment. Thus, A obtectus females seem to measure only relative seed size when a comparison is possible. Nevertheless, females overload seeds with eggs and this can result in larval competition, so that, whereas resource size assessment and a robust egg-load adjustment indicate a trade-off between resource use and female fitness, it does not seem to provide much benefit for the progeny in stored dry beans. Several features, eg the use of oviposition markers and its consequences, may counterbalance the possible negative effects. It is assumed that, due to life cycle differences, females in the bean field may realise different fitness gains in comparison with those living in stores.