Bacillus thuringiensis (Bt) produces a variety of insecticidal crystal proteins and widely used as one of the most successful biological control agents. Recently, studies that introduce cry genes into crops to create pest resistance have made much progress, and the total area of land planted with Bt crops has increased substantially. In this study, pest resistance of 8 transgenic Bt rice events with a synthetic cry1Ac gene linked to rice rbcS-tp sequence were assessed under laboratory conditions. Bioassays were performed against Cnaphalocrocis medinalis, which is a significant pest of rice in Asia. C. medinalis larvae were shown to be susceptible to all eight events, even though there were differences between the causes of death. The results differed between developmental stages of the larvae, despite the fact that all 8 events led to high mortalities. These results may be a significant foundation for the evaluation of improved transgenic Bt rice.

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.

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.