Preference for magnesium sulfate-treated leguminous seeds in egg-laying bean weevil (Acanthoscelides obtectus say, col., bruchidae).

Unlike many secondary plant substances, a wide range of concentrations (4-1000 mM) of magnesium sulfate, applied to dry beans, significantly increased egg-laying by the dry bean weevil in binary choice tests, in favor of treated seeds. No other magnesium-containing compounds studied exerted such an effect, nor was a similar response noted on treated beans in no-choice situations. The total number of eggs laid per female was in the same range in both types of test. Variably enhanced or suppressed oviposition responses were shown on magnesium sulfate-treated secondary hosts and on nonhosts or on indifferent substrates. No specific behavior by egg-laying bean weevil females on Mg-treated seeds could be detected. The results are explained by assuming the functioning of magnesium as a supernormal stimulus for egg-laying. However, a physiological effect on neuromuscular synaptic transmission, as a consequence of probable Mg uptake resulting in a decreased propensity to move, is also hypothesized.