The α-galactoside binding lectin fromArtocarpus hirsutainhibits growth and has anti-fertility activity onTribolium castaneum(Herbst) (Coleoptera: Tenebrionidae) (red flour beetle). Postembryonic development was affected to a significant level when freshly hatched first instar larvae ofT. castaneumwere fed on a lectin-treated diet at 0.5% (w/w) concentration. Although larval survival till the tenth day did not differ significantly, larval weight did. Similarly, time taken for pupation, percentage pupation, time taken for adult emergence and percentage adult emergence were adversely affected. Larval-pupal intermediates comprised 11% and pupal-adult intermediates comprised around 50% of the treated population after 30–35 days. Finally, the F1 breeding pairs completely failed to reproduce successfully since the female adults from the breeding pairs were unable to lay a single egg.