Insect growth regulators (IGRs) are attractive pest control agents due to their high target specificity and relative safety to the environment. Recently, plants have been shown to synthesize IGRs that affect the insect juvenile hormone (JH) as a part of their defense mechanisms. We identified several JH agonists (JHAs) and antagonists (JHANs) from plant essential oil compounds using a yeast two-hybrid system transformed with the Aedes aegypti JH receptor as a reporter system. They showed high mosquitocidal activities with relatively low LC50 values and caused retardation of ovarian development in female mosquitoes. While the JHAs increased the expression of JH-induced gene, the JHANs caused reduction in the expression of the same gene. The compounds identified in this study could provide insights on the plant-insect interactions and may be useful for the development of novel IGR insecticides.

Insect growth regulators (IGRs) are compounds that induce developmental anomalies such as premature molting or supernumerary larval stages. IGRs can be divided into 3 groups based on their mode of action, one of which is known as the juvenile hormone agonists (JHAs). Previously, we have developed a novel screening method which can identify juvenile hormone antagonists (JHANs) using a yeast-two hybrid system incorporating Aedes aegypti juvenile hormone receptor complex proteins (MET and FISC). It has been reported that plants may use IGRs in their defenses against insect herbivores. In this study, 171 plant essential oil samples were screened using the yeast-two hybrid system in order to identify JHAs and/or JHANs. Eight out of 171 samples, 4 JHA and 4 JHAN candidates, were selected and their insecticidal activities were investigated against A. aegypti larvae. They showed high levels of insecticidal activities, with LC50 values ranging from 11.2~21.4 ug/ml. These results indicate that plants do use JHAs and/or JHANs as a part of their defenses against insect herbivores. Also, JHAs and JHANs identified in this study could be exploited as effective biological control agents.