During the larval development process of insects, juvenile hormone (JH) is essential for regulating various aspects of larval life, including growth, reproduction, and behavior, throughout their larval stage. The larval stage of Spodoptera frugiperda, when it consumes plant-derived metabolites, develops into pupae, but these pupae are unable to molt successfully. In this way, plant-derived metabolites contain or produce inhibitors of juvenile hormone, thereby disrupting the development of insect larvae and making them vulnerable to harm. Therefore, in this study, we established an in vitro screening system using yeast cells transformed with the Met-SRC juvenile hormone receptor of S. frugiperda. Through this system, we were able to identify juvenile hormone disruptors from plant-derived metabolites and confirm their developmental inhibitory effects on the larvae of S. frugiperda.

Plant essential oils have been reported to show repellent, insecticidal and growth-reducing effect on many insect herbivores. Recently, it has been reported that plants synthesize secondary metabolites regulating insect juvenile hormone (JH) receptor complex as a part of their defense mechanisms. We tested 180 plant essential oil compounds using a yeast two-hybrid system transformed with the Aedes aegypti JH receptor as a reporter system. Among them, we identified 17 compounds that showing high JH agonist (JHA) or antagonist (JHAN) activities. They were grouped into 4 groups by their structural similarity and their insecticidal activity was tested against larvae of Aedes albopictus, Plutella xylostella, Plodia interpunctella and Laodelphax striatellus. These results could provide insights on the plant-insect coevolution and may be useful for the development of insect specific and safe pesticides.

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.

Insects impact human health through vector-borne diseases and cause major economic loses through damaging crops and stored agricultural products. Insect-specific growth regulators (IGR) represent attractive control agents because of their safety to the environment and humans. Here, we report identification of plant compounds that are antagonists of the insect-specific juvenile hormone (PJHANs), using the yeast two hybrid system transformed with the mosquito JH receptor as a reporter assay. We show that these compounds act by inhibiting larval growth and reproduction in mosquitoes. We also demonstrate that PJHANs affect the JH receptor, Methoprene-tolerant (Met), by disrupting its complex with CYCLE, formation of which is required for mediating JH action. We isolated five diterpene secondary metabolites with JH antagonist activity from two plants, Lindera erythrocarpa and Solidago serotina. They are effective in causing mortality of mosquito larvae at relatively low LD50 values. Two of these diterprenes affect Met function, leading to reduction in expression of Met target genes and causing retardation of follicle development in mosquito ovaries. Developing potent compounds counteracting JHaction (JH antagonists) would find a wider range of control applications. However, so far such JH antagonists have not been developed. Here, we report the discovery of potent JH antagonists in plants, which represents an innate resistance mechanism of plants against insect herbivores. These newly discovered plant JH antagonist compounds could be used as the starting material for developing novel insecticides.