A species‐specific ELISA has been developed for quantitatively detecting the presence of the granary weevilSitophilus granariusin grain. The assay is based on the use of monoclonal antibodies (MAb) and polyclonal antibodies (PAb) directed against a 59 500 Da protein fromS. granarius.This protein, tentatively termed the W protein, has an isoelectric point of 6–0. Two MAb to the W protein were obtained that exhibited clear specificity and did not react by ELISA with closely related species. Both MAb and PAb against the Wprotein were used to develop a specific sandwich ELISA immunoassay to estimate the proportion ofS. granariusin an infesting insect population in wheat. The assay reported here also lays a foundation for the further development of MAb‐based ELISA techniques for detecting specific insect species in contaminated grain.