Insect growth regulators (IGRs) are insecticides that disrupt the normal development of target insects by inducing symptoms such as premature molting or supernumerary larval stages. IGRs are categorized into three types based on their mode of action. One of the them is classified as juvenile hormone agonists (JHAs). In recent studies, we identified juvenile hormone antagonists (JHANs) from plant extracts. In order to identify a novel juvenile hormone agonists and antagonists, we tested 2,354 chemical compounds using the yeast-two hybrid system. Among them, 2 JHAs and 4 JHANs were selected and their insecticidal activities were evaluated against Aedes albopictus larvae. These results may be useful for 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.

Insect growth regulators (IGRs) are insecticides that disrupt the normal development of target insects by inducing symptoms such as premature molting or supernumerary larval stages. IGRs are categorized into three types based on their mode of action. One of the them is classified as juvenile hormone agonists (JHAs). Recently, we developed a yeast-two hybrid system that can identify potential juvenile hormone antagonist (JHAN) candidates using Aedes aegypti juvenile hormone receptor complex proteins, known as MET and FISC. In order to identify novel JHAN compounds, approximately 8,700 basic chemical compounds were screened using the yeast-two hybrid system. Among them, 35 compounds were first selected based on consistency of JHAN　activity, and their insecticidal activities were investigated against A. aegypti larvae. These compounds showed insecticidal activities about 1.7~3 times higher than that of pyriproxifen, which is a well known JHA insecticide. These results suggested that these JHANs can be used as effective JHAN insecticides.

Insect Growth Regulators (IGRs) are insecticides that disrupt the normal development of target insects by inducing symptoms such as premature molting or supernumerary larval stages. Juvenile hormone systems become the targets of two types of IGRs: the Juvenile Hormone Agonists (JHAs) and Juvenile Hormone Antagonists (JHANs). Pyriproxyfen is one of the chemical compounds widely used as JHA to control many kinds of insects while Kanakugiol is a plant-extracted compound which acts as JHAN. The small brown planthopper, Laodelphax striatellus, is one of the most serious pest insects of rice plants because it can transmit the rice stripe virus which often causes significant reduction of yield in the field. In order to analyze the differential gene expressions of L. striatellus upon JHA and JHAN treatment by using next generation sequencing technique, we sprayed Pyriproxyfen and Kanakugiol on 4th instar nymphs of L. striatellus respectively, and extracted total RNA for RNA-seq. The quality-filtered Illumina sequence reads of the control, JHA, and JHAN treated samples were mapped to the reference gene sequences by using the Bowtie2 software. Then the results of mapping by Bowtie2 were analyzed by eXpress software to quantity the differential gene expression.

Recently, Bacillus thuringiensis (Bt) cry genes encoding insecticidal Cry proteins have been widely applied for the construction of transgenic crops resistant to insect pests. This study aimed to construct novel mutant cry1Ac genes for genetically modified crops with enhanced insecticidal activities. Using multi-site directed mutagenesis, 34 mutant cry1Ac genes were synthesized and converted at 24 amino acid residues, located on domain I (8 residues) and domain II (16 residues). These mutant genes were expressed as a fusion protein with polyhedrin using the baculovirus expression system. The expressed proteins were occluded into polyhedra and activated stably to 65 kDa by trypsin. Among these, Mut-N04, N06, and N16 showed high levels of insecticidal activites against larvae of Plutella xylostella, Spodoptera exigua, and Ostrinia furnacalis. Mut-N16, which showed the highest insecticidal activity, is expected to be a desirable cry gene for introduction into transgenic crops. This study could provide useful means to construct mutant cry genes with improved insecticidal activities and expanded host spectrum for transgenic crops.

Rice stripe virus (RSV) is one of the serious plant pathogenic viruses for rice transmitted by small brown planthopper, SBPH, Laodalphax striatellus. RNA interference (RNAi) is an universal gene-knockdown mechanism in eukaryotic organisms which includes insects，and has been considered as an alternative strategy to control insect pests. Hence, we applied this technique to interfere the translation of target RNA genes to knockdown the virus gene on RSV-viruliferous L. striatellus. Three out of seven RSV genes, RdRp, NS3, and NCP were used as target genes and each dsRNA targeting the viral genes were delivered to the insects indirectly through the rice leaves by irrigation. As a result, not only the relative expression level of target genes decreased but also those of non-target genes and the replication of RSV genome as well. In summary, leaf-mediated dsRNA feeding methods would be useful in the knockdown of target genes on piercing-sucking insects. The genes used in this experiment can be utilized for the development of pest-resistant transgenic plants based on RNAi.

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.

Rice stripe virus (RSV) is one of the serious plant pathogenic viruses for rice and mediated by small brown planthopper, Laodalphax striatellus. So far, the studies have been mainly focused on the interaction between the host plant and the virus. In this study, for better comprehension of the interactions among Rice stripe virus, rice and small brown planthopper, transcriptomes of the RSV-viruliferous (RVLS) and non-viruliferous L. striatellus (NVLS) were comparatively analysed. For this, non-viruliferous L. striatellus were collected from non-infected rice field and fed RSV-infected rice for 5 days. With the RNAs prepared from the RSV-viruliferous and the non-viruliferous small brown planthoppers, we conducted Illumina RNA sequencing (Hiseq 2000) and then two transcriptome databases were generated from RVLS and NVLS, respectively. The transcriptome of RVLS and NVLS were campared to figure out how the gene expression of the insects affected by Rice Stripe Virus. RSV-dependently regulated genes analysed from this study may have important functions in the transmission and replication of RSV.