The topical, fumigant and ovicidal activity of fourteen monoterpenoids and thirty-one monoterpenoid derivatives were evaluated using the house fly, Musca domestica. The toxicity data of acyclic, monocyclic, and tricyclic phenols, alcohols, and ketones were compared to determine structure-activity relationships involving the monoterpenoids' structural shape, type of functional group, and degree of saturation. Monoterpenoid acetate, propionate, pivalate, trichloroacetate, and trifluoroacetate derivatives were synthesized and their insecticidal activities were evaluated. The toxicities of the monoterpenoid acetate and haloacetate derivatives were compared with each other and the parent alcohols or phenols to evaluate the influence of derivatization on toxicity. Monoterpenoid ketones were more insecticidal than alcohols in the topical and ovicidal bioassays. Pivalate and acetate derivatives were more toxic than the haloacetate derivatives in both the topical and ovicidal bioassays. Thymyl trifluoroacetate was the most effective fumigant followed by menthol and fenchone. Thymol and geranyl acetate were the most insecticidal monoterpenoid and monoterpenoid derivative in the topical bioassays. Geraniol, geranyl propionate, terpineol, carvacrol and menthone were as ovicidal as the pyrethrin standard.