Larvae of the Mediterranean flour moth (Anagasta kuehniella Zeller) cause major losses in stored grains throughout the world. In this study, pouterin, a lectin-like protein isolated from Pouteria torta (Mart.) Radlk. seeds, was tested for activity against A. kuehniella larvae. Pouterin did not produce significant effects on survival; however, at c. 1% w/w concentration in artificial diet, it produced a 71.4% reduction in average weight of the larvae. A dietary utilisation assay showed a reduction in efficiency of conversion of ingested food, efficiency of conversion of digested food and approximate digestibility, as well as an increase in metabolic cost. Pouterin increased the level of trypsin in the midgut and faeces of larvae. We conclude that pouterin possesses an insecticidal effect against A. kuehniella larvae and this effect may be mediated by the binding of pouterin to chitin components of the peritrophic membrane, or glycosylated proteins in the insect midgut.