Impact of egg-mass detrition of European corn borer,Ostrinia nubilalis(Hübner), on estimation of egg-mass density in a cornfield was investigated. Both an average and worst-case detrition rate curve were estimated from field egg-mass counts. At 50% completion of a 20-day symmetric oviposition period, 1.14 and 1.46% of egg masses deposited were predicted missing using these curves. Of 20 cornfields observed between 1982 and 1983, the management decision was never changed as a result of correcting for egg-mass detrition.