곤충생장조절제(IGR)은 대상 해충에 대한 특이성이 높고 환경에 대한 독성이 상대적으로 낮다는 장점으로 유기합성 살충제를 효과적으로 대체할 수 있는 유망한 수단으로 여겨진다. 현재 시판되는 곤충생장조절제는 작용 기작에 따라 유충호르몬 작용제(JHA), 탈피호르몬 작용제 (EA) 및 키틴 합성 저해제(CSI)의 세 가지로 구분된다. 최근 들어, 이집트숲모기의 Met과 FISC/CYC 유전자를 yeast two-hybrid system에 도 입하여 유충호르몬에 의해 매개되는 Met과 FISC/CYC의 결합을 in vitro에서 구현하였으며, yeast two-hybrid β-galactosidase assay를 통하 여 식물과 미생물 및 화합물 library로부터 다양한 유충호르몬 길항제(JHAN)가 분리되고 있다. 유충호르몬은 곤충의 발달, 생식, 휴면 등을 포함 한 다양한 생리 작용을 조절하기 때문에, 유충호르몬 길항제는 대상 해충의 내분비 신호 전달을 방해하여 비정상적인 발달 및 유충 단계에서의 치 사를 초래하며, 이는 유충호르몬 길항제가 넓은 기주 범위를 가진 살충제 개발에 효과적으로 이용될 수 있다는 것을 시사하였다. 따라서 본 논문 에서는 유충호르몬 길항제의 작용점인 Met에 의해 매개되는 유충호르몬의 신호 전달 체계와 친환경 살충제로서의 유충호르몬 길항제의 전망에 대해 알아보고자 하였다.

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.

Recent studies suggested that gut symbionts modulate insect development and reproduction. However, how gut symbionts modulate host physiologies and what types of molecules are involved in these changes are still unclear. When we analyzed hemolymph proteins and transcriptional levels of host insects, hexamerin-α (Hex-α), hexamerin-β (Hex-β) and vitellogenin-1 (Vg-1) were highly expressed in symbiotic insects (Sym) compared to aposymbiotic insects (Apo). Depletion of Hex-β by RNA interference in 2nd Sym-nymphs delayed adult emergence, whereas Hex-α and Vg-1 RNA interference in 5th nymphs decreased reproduction of female insects and caused loss of color of laid eggs. Also, the levels of JHSBIII of Riptortus host were 3-fold higher in the Sym-female insects compared to the Apo-insects. These results demonstrate that the Burkholderia gut symbiont modulates host development and egg production through regulating the expression of three host storage proteins by controlling of brain hormone.

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.

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.

The Riptortus-Burkholderia symbiosis is a newly emerging insect-bacterium symbiotic system. This symbiosis system has a good merit as an experimental model system to produce the non-symbiotic (apo) and symbiotic (sym) host insect. In recent reported papers, the symbionts play important biological roles for the host insects. Meanwhile, juvenile hormone (JH) is one of major hormone synthesized corpora allata(CA) to control many physiology of insect. However, the study for cross-talk mechanism between symbionts and host hormones to control important physiological phenomenon of insects is almost none. In this study, we found that Riptortus speed up adult emerging and increase egg laying on presence of symbiont Burkholderia. Also we found that hexamerin proteins, which were controlled the expression by JH, were accumulated in sym-Riptortus hemolymph compare with apo-Riptortus. According as combined results, we hypothesized that the gut symbiont Burkholderia can control JH titer to conclude out beneficial effects such as development and reproduction of R. pedestris. To verify this hypothesis, we examined measurement of JH titer, expression of hexamerins as JH response genes and RNAi for hexamerin protein during whole Riptortus life on presence or absence of symbiont Burkholderia. All results demonstrated that gut symbiont controlled JH titer of Riptortus. Controlled JH amount by symbiont Burkholderia in host midgut regulated hexamerin protein expression for speeding up adult emerging and increasing egg production.

Neuropeptides are the largest group of neurohormones that act in intercellular communication to regulate various physiological and behavioral events during development and reproduction in animals. One of these families is Pyrokinin/PBAN (Pheromone Biosynthesis Activating Neuropeptide) family defined by a similar 5-amino-acid C-terminal sequence (FXPRLamide) that is the active core fragment for these peptides. This motif has been identified from a variety of insect orders, and even a crustacean species. This family of peptides has been implicated in various physiological functions: 1) moth pheromone biosynthesis, 2) larval melanization, 3) moth embryonic and pupal diapause, 4) visceral muscle contraction in the cockroach, 5) fly puparium formation in different insect species. To date, ~159 PBAN/Pyrokinin family peptides have been identified from 40 species. It is one of the largest neuropeptide families in insects; however, the physiological function of most of these peptides is unknown. The mechanism of PBAN control over pheromone production is only well defined for sex pheromone biosynthesis in a limited number of lepidopteran moths. No other insect groups have been reported to regulate pheromone biosynthesis using PBAN. Conventional insecticides target synapses and/or sodium channels that result in neurotoxicity in the nervous system. Unfortunately, this mode of action affects non-target animals as well. These methods remain the major tool for pest control, and the side effects cause many global problems that result in increased environmental and human health expenses. Therefore, we are faced with a requirement to develop new targeted control agents that will lead to pesticides with new modes of action. This is not impossible, but not easy. Every species-specific neuropeptide is expected to play a critical physiological function in metamorphosis and development of insects. There are no exceptions. Our long-standing question is – “how can interference/disruption ofthe insect (neuro)hormonal system be used to discover novel control tools”. To solve this question a novel approach is being applied for finding and screening novel agonist and/or antagonist to gene products, neuropeptide and receptor, from the in vitro system and through virtual modeling. This concept will be a new paradigm opening the window for the next generation of the pest control, and the principle method will be adapted for insect specific pests. Another research interest here will be presented on exocrinal products, such as semiochemicals produced from insects and plants for chemical communication that regulates insect/insect and insect/host interactions. These studies have included the identification of pheromones and the biosynthetic pathway of their production from insects. The ultimate goal of this research is to discover novel biologically-based green pesticides that are environmental-friendly pest control alternatives.