Influence of dietary applied monoterpenoids and derivatives on survival and growth of the European corn borer (Lepidoptera : Pyralidae)

Sixteen natural monoterpenoids and 6 synthetic derivatives were selected Fo r study of larvicidal activity and growth inhibitory effect against the Eur opean corn borer, Ostrinia nubilalis (Hubner). For this study, 2 different dietary exposure bioassays were used: compounds applied on the diet surface (on-diet), and compounds incorporated into the diet (in-diet). Most of the monoterpenoid compounds showed some degree of larvicidal activity in both bioassay procedures after a 6-d exposure period. Among the monoterpenoids, pulegone was the most active. Larvicidal toxicities were significantly enha nced for the structurally modified compounds; monoterpenoid derivatives MTE E-25 (2-fluoroethyl thymyl ether) and MTEE-P (propargyl citronellate) were most toxic to borer larvae. When reared on diet containing the monoterpenoi ds or their derivatives, changes in developmental parameters and pupal weig hts of the European corn borer also were noted when they were fed several o f the compounds. Some larvae reared on treated diet with higher concentrati ons of the test compounds died before pupating. In general, growth and deve lopment of the European corn borer were affected by monoterpenoid compounds , and some compounds such as I-menthol, pulegone, MTEE-25, and MTEE-P acted as insect growth inhibitors.