Monoterpenoids are naturally occurring compounds that are found in higher-order plants. These compounds are secondary metabolites that seem to play no major role in the metabolic functioning of the plants. One role of monoterpenoids in the plants is to defend against plant-directed pathogens, herbivores, or competing plant species. These compounds are good leads for synthesis or isolation of more effective insecticides. To accomplish these goals, we developed quantitative structure−activity relationships (QSARs) in order to predict insect toxicity of monoterpenoids and derivatives that have not yet been synthesized or experimentally tested. Correlations were found between toxicity and certain quantum and traditional chemical parameters. We found a linear relationship between LD50 values for house fly toxicity and Mulliken populations in aromatic monoterpenoids. Multiple linear regression of an E-State descriptor and a GETAWAY (GEometry, Topology and Atomic Weights AssemblY) descriptor also showed a relationship with house fly toxicity for a wide range of monoterpenoids.