Honeybees are inevitably threatened by various pathogens including Sacbrood virus (SBV) and Galleria mellonella. Recently, RNA interference (RNAi) has been suggested as a promising strategy for suppression of honey bee viruses. Also, Bacillus thuringiensis (Bt) has been widely applied for the control of lepidopteran pests such as G. mellonella. In this study, it was intended to develop dsRNA production platform using Bt. For this, the pHT1K-SBV vp1 vector which transcribes sense and anti-sense SBV vp1 gene under control of Cyt1Aa sporulation-dependent promoter was introduced into Bt strain NT0423 expressing Cry1-types toxins. SBV replication was suppressed in the worker A. cerana ingested dsRNA produced from the Bt transformant. Crystal proteins from the Bt transformant showed high level of insecticidal activity against 4th instar larvae of G. mellonella.

Mosquitoes are medically important insect pests that act as vectors of various diseases when they feed on humans. Insect growth regulators (IGRs) could become an effective alternative to control mosquitoes because of their high specificity and relatively low toxicity to environment. Recently, we have developed high-throughput juvenile hormone antagonist (JHAN) screening system based on yeast-two hybrid assay. Actinomycetes have been reported to produce various bioactive compounds including insect growth regulators (IGRs). In this study, culture filtrates and mycelia extracts of 2,875 actinomycetes isolates screened for their IGR activities and mosquitocidal activities. Among 75 culture filtrates and 17 mycelia extracts with JHAN activities, 19 culture filtrate and 3 mycelia extracts showed high level of mosquitocidal activities against 3rd instar larvae of Aedes albopictus. These results suggested that secondary metabolites of actinomycetes could be used as environmentally benign mosquitocidal agents.

In order to investigate novel insect growth regulators (IGRs) from actinomycetes, 363 isolates of actinomycetes were tested for their IGR activities. Among them, Streptomyces sp. AN120537 showed the highest juvenile hormone antagonist (JHAN) activity and significant insecticidal activities against larvae of Aedes albopictus and Plutella xylostella. In addition, the dead larvae showed morphological deformities such as contraction of body segments or pigmentation of all body parts. Through liquid chromatography and bioassay-guided fractionation, 7 IGR compounds were identified from the crude hexane extract of AN120537. These results suggested that Streptomyces sp. AN120537 could be useful resources for development of eco-friendly insecticidal agents.

RNA interference (RNAi) has been considered as an alternative strategy to control agricultural pest whereby double-stranded RNA triggers a potent and specific inhibition of its homologous mRNA. Since small dsRNAs are required for various RNAi applications, there is a need for cost-effective methods for producing large quantities of high-quality dsRNA. In this study, Bacillus thuringiensis (Bt) based dsRNA production platform was established under control of sporulation-dependent promoter and vp1 gene of Sacbrood virus (SBV) was introduced. The dsRNA against vp1 gene produced from the Bt suppressed the replication of SBV. In addition, the dsRNA was assembled into inulin coated-nanoparticle to increase stability of dsRNA in environment.

Streptomyces has been reported to produce various secondary metabolites which have the potential to become environmentally safe insecticides. In this study, 1,274 streptomyces culture filtrates were screened for their JHAN activity in order to identify novel insecticidal compounds. 34 isolates with high levels of JHAN activity were selected, and their insecticidal activities were tested against Plutella xylostella larvae. Among them, IMBL-263 which was revealed to be Streptomyces anulatus by 16s rRNA sequencing showed the highest insecticidal activity. Also, systemic activities of secondary metabolites extracted from the S. anulatus on plant, Brassica napus, were investigated. These results suggested that secondary metabolites from the S. anulatus might be useful for development of novel environmentally benign insecticides.

The development of entomopathogenic fungi has received increasing interest as part of integrated pest management strategies as biocontrol agents. It is reasonable to assume that entomopathogenic fungi might produce secondary metabolites modulating juvenile hormone for their survival against defense mechanisms of host insects. In this study, acetone extracts of 189 entomopathogenic fungi cultured on unpolished rice medium were screened for their juvenile hormone antagonist (JHAN) activities using the yeast-two hybrid system. Among 14 extracts showing JHAN activities, extract of the F-145 showed high level of insecticidal activities against both Plutella xylostella and Aedes albopictus. This isolate was identified as Lecanicillium attenuatum. These results suggested that the Lecanicillium attenuatum could be useful for development of eco-friendly insecticides.

Beet armyworm, Spodoptera exigua, is known to be hard-to-kill pest by having high resistance to insecticides and its control is intensely dependent on fewer insecticides. In this study, the ethyl acetate extract of Streptomyces sp. was evaluated to find novel insecticidal agents against S. exigua. In order to determine the identity of insecticidal compounds, the crude ethyl acetate extract was fractionated based on the TLC profiling and bioassay-guided monitoring. These results indicated that the non-polar fraction have high level of insecticidal activity against second instars of S. exigua. These findings suggested that secondary metabolites produced by Streptomyces sp. could be considerable potential resources as novel insecticidal formulation candidates.

Insect growth regulators (IGRs) are insecticides that disrupt the normal development of target insects. Among the IGR insecticides, juvenile hormone (JH)-related IGRs are of particular interest because they stimulate or interfere with the formation of JH receptor complex. In the precious studies, novel JH-related IGRs with JH agonist (JHA) and antagonist (JHAN) activity were identified by using yeast two-hybrid system transformed with the Aedes aegypti JH receptor complex. In this study, the transcriptomic responses of Aedes albopictus were investigated upon JHA and JHAN, respectively. These results will provide important information about understanding of impact of JH-related IGRs in transcription level.

Entomopathogenic fungi have been widely studied for their potential as the effective biological control agents. Theyproduce variety of secondary metabolites with insecticidal activities, and it is reasonable to assume that entomopathogenicfungi might produce secondary metabolites modulating juvenile hormone for their survival against defense mechanismsof host insect. In this study, Acetone extracts of 189 entomopathogenic fungi cultured on unpolished rice medium werescreened for their juvenile hormone antagonist (JHAN) activities using the yeast-two hybrid system. Among them, 14extracts showed high level of JHAN activities and their insecticidal activities against Aedes albopictus were investigated.

The small brown planthopper (SBPH), Laodelphax striatellus, is one of the most serious pest insects of rice plants.Buprofezin has been used to control SBPH for more than a decade, however, the occurrence of buprofezin resistant SBPHwas reported recently. To develop an alternative pest control an alternative pest control strategy, RNA-seq of buprofezin-treatedSBPH was performed to screen the insecticidal target genes for RNA interference (RNAi). Six genes were selected fordsRNA synthesis, and applied to SBPH to assess the insecticidal efficacy. Two and three of those dsRNAs showed moderatedand substantial insecticidal activity up to 60% of mortality in one week, respectively. These results demonstrated the potentialof gene screening strategy for the development of RNAi-based pest management program.

Widespread use of chemical insecticides has resulted in development of insect resistance and natural products withbiological activities could become an attractive alternative to control insect pests. In order to find more effective insecticidesfor controlling mosquito, various mosquitocidal compounds are studied. Recently, juvenile hormone antagonists (JHANs)are known to be to safe and effective insecticides for control mosquito. In order to identify novel insecticidal compoundswith JHAN activity, several chalcones were surveyed on their JHAN activities and larvicidal activities against Aedes albopictuslarvae. Among them, 2’-hydroxychalcone and cardamonin showed high level of JHAN and mosquito larvicidal activities.These results suggested that chalcones with JHAN activity could be useful for control of mosquito larvae.

Actinobacteria have been known to produce variety of bioactive metabolites that include antibiotics and plant growthfactor. Also, Insecticidal compounds such as avermectin and tetranectin have been reported from actinobacteria. In thisstudy, to identify novel insect growth regulator (IGR)-based insecticidal compounds, 1,283 actinobacteria isolates weretested for their juvenile hormone antagonist (JHAN) activity using the yeast-two hybrid β-galactosidase assay. Amongthem, 25 isolates showed high level of JHAN activity and insecticidal activity against 3rd larvae of diamondback moth,Plutella xylostella. These results suggested that actinobacteria could be unparalleled source of novel IGR-based compounds.

Recently, it has been reported that plants produce variety of phytochemicals against insect pests as a part of their defencemechanism. In this study, to identify novel compounds that disrupt juvenile hormone (JH) receptor complex, plant essentialoil compounds were tested using in vitro yeast two-hybrid system transformed with the Aedes aegypti JH receptor complex.Among the plant essential oil compounds, farnesol interfered with pyriproxyfen-mediated binding of A. aegypti Met-FISC.In contrast, farnesyl acetate induced the binding of A. aegypti Met-FISC. Also, both compounds caused retardation ofovarian development and change of transcription level in female A. albopictus. These results could provide insights onthe plant-insect coevolution and may be useful for the development of insect specific and safe pesticides.

Streptomyces species have been studied to find potent pest control agents as an alternatives to chemical insecticides.Previously, one of the ethyl acetate extract of Streptomyces isolates cultured on unpolished rice medium showed highlevel of juvenile hormone antagonist and larvicidal activities against pest insects including Aedes albopictus, Plutella xylostellaand Laodelphax striatellus. It has been known that the biosynthesis of secondary metabolites of Streptomyces could beinfluenced by a variety environments such as nutritional composition and growth conditions. In this study, to optimizeculture conditions for stable production of insecticidal compounds from this isolate, binding assay and bioassay-guidedmonitoring were conducted using various culture conditions.

RNA interference (RNAi) has been considered as an alternative strategy to control agricultural pests whereby double-strandedRNA triggers a potent and specific inhibition of its homologous mRNA. Since small double-stranded RNAs are requiredfor various RNAi applications, there is a need for cost-effective methods for producing large quantities of high-qualitydsRNA. Bacillus thuringiensis produces much insecticidal proteins with expression of their encoding genes being drivenby sporulation-dependent promoters. To develop dsRNA mass-production platform utilizing Bt, the pHT1K-EGFP plasmidvector which has cyt1Aa sporulation-dependent promoter was constructed. The transcriptional level of target gene (EGFP)is higher 113 times than Bt reference gene (ssPE). It was applied to protect honeybee from Sacbrood virus, so targetgene was replaced to SBV-vp1. By ingestion of Bt-derived dsRNA to honeybee shows positive effect on SBV suppression.

Secondary metabolites isolated from Actinomycete have been studied to find potent pest control agents as their insecticidal and growth inhibitory activities. In order to investigate novel insecticidal compounds, second metabolites from 363 Actinomycete isolates were evaluated for their insect growth regulatory activities. Among them, ethyl acetate extracts from ten Streptomyces spp. showed high level of Juvenile hormone antagonist activity. In addition, their insecticidal activities were tested against larvae of Aedes albopictus, Plutella xylostella and Laodelphax striatellus. These results suggested that secondary metabolites from Streptomyces spp. could be used for development of novel IGR-based insecticides.

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.

RNA interference (RNAi) is an universal gene-knockdown mechanism in eukaryotic organisms including insects. RNAi has been considered as an alternative strategy to control agricultural pests whereby double-stranded RNA triggers a potent and specific inhibition of its homologous mRNA. Bacillus thuringiensis (Bt) is a spore-forming bacterium that produces a copious amount of crystal proteins δ-endotoxins under the control of sporulation-dependent promoter. In order to develop dsRNA mass-production platform utilizing recombinant Bt, the pHT1K-EGFP which expresses dsRNA against EGFP under the control of Cyt1-Aa sporulation-dependent promoter was constructed and the expression level of transgene (EGFP) was confirmed by qPCR analysis. These results suggested that Bt’s potential of becoming a new platform in dsRNA production.

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 (JH)-based IGRs are of particular interest because they simulate or interfere with the formation of juvenile hormone receptor complex. Insect larvae generally have been poorly susceptible to JH agonists (JHAs) because endogenous JH titer is already high in the larval stage. In contrast, JH antagonists (JHANs) might be more effective for control of target pests in larval stages through interference in the status quo action of JHs. In this study, we tested 2,354 chemical compounds using the yeast-two hybrid system to identify JHANs. Among them, K265674 sample was selected and its insecticidal activity was evaluated against Aedes albopictus larvae. These results may be useful for development of novel IGR insecticide.

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) was recently suggested as a promising strategy for controlling insect pests, including those that serve as important vectors for plant pathogens. To disturb transmission of the RSV in SBPH using RNAi pathway, we chose nine genes highly expressed in RSV-viruliferous SBPH by transcriptome sequencing. These SBPH-derived dsRNAs were applied to the insects indirectly through xylem of rice leaves by irrigation. qPCR result demonstrated that five out of nine SBPH-derived dsRNAs successfully reduced the replication of RSV in viruliferous SBPH in dose-dependent manner, suggesting that these five dsRNAs could suppress replication of RSV and provide a new tool for RSV control strategy.