Conjugated linoleic acid (CLA) refers to a group of positional and geometric isomers of octadecadienoic acid with double bonds most commonly found in the 9 and 11 or 10 and 12 positions. CLA has been shown to incorporate in the egg yolk lipids and body tissues of hens fed a CLA-enriched diet. Altered egg lipid fatty acid profiles, decreased egg production, and decreased egg hatchability also have been demonstrated in poultry fed CLA-enriched diets. House flies were shown to incorporate CLA in body tissues while no adverse effects on development were noted. However, we have observed that European corn borers (ECB), Ostrinia nubilalis, exhibit adverse effects in response to dietary CLA; they demonstrated decreased survival and an increased growth period. Our objectives in this study are to examine the effect of dietary CLA on the fatty acid profile of pupal and adult corn borers, fecundity, and fertility of the eggs. CLA isomers incorporated into pupal and adult tissues in a dose-dependent manner. An increase in saturated fatty acids and decrease in polyunsaturated fatty acids were found in lipids of ECB fed CLA-enriched diets. We expect to find decreased egg production and fertility of eggs from adults reared on CLA-enriched diets.