Lycoriella pleuroti is a pest of edible fungi, commonly cultured on a cottonseed shell–based medium. L. pleuroti larvae were reared on culture media containing variety CRI30 (transgenic Bacillus thuringiensis [Bt]) cottonseed, variety CRI16 (nontransgenic) cottonseed, Bt (CryIAc) protein, gossypol, tannin, and quercetin. The mortality of larvae reared on media with CRI30 cottonseed was significantly higher than that of larvae reared on media with CRI16 cottonseed, and mortality increased with increasing CRI30 and CRI16 cottonseed content. Media containing Bt protein, gossypol, tannin, and quercetin negatively influenced survival of L. pleuroti larvae. Of the four ingredients, the negative effects of gossypol and tannin were the largest. The suppression caused by the Bt protein was not as great and did not increase with increasing dose. The presence of quercetin also increased larval mortality over the control, but mortality decreased with increasing quercetin content.