Research

Hormonal regulation of insect molting and metamorphosis

Insect molting and metamorphosis are regulated by the molting hormone (ecdysone) and juvenile hormone (JH). JH is an anti-metamorphic hormone that suppresses metamorphic changes. Recently, several researchers succeeded in identifying some of the factors in JH signaling pathway: methoprene-toletant (Met) is likely the JH receptor, while Krüppel homolog 1 is a JH-response transcription factor downstream of Met. Many of these studies were performed by RNAi experiments using the red flour beetle, Tribolium castaneum.

We are trying to elucidate the molecular mechanism of JH signaling in a variety of pest species. These studies will help us to develop new insect growth regulators that are specifically effective against the target pest.

Insect immune system in Beetles

Insects produce antimicrobial peptides (AMPs) as part of their humoral immune system against foreign organisms. The mechanism by which AMP gene expression is regulated upon recognition of foreign substances has been studied in detail in model insects such as Drosophila melanogaster. As a result, the signal transduction pathway that leads to AMP gene expression via the Toll or Imd pathway, depending on the type of microorganism infected, has been clarified. Our research is aimed at elucidating the regulatory mechanism of AMP gene expression in Coccinellidae, a type of beetle. Recent experimental results have revealed the interesting finding that the regulatory mechanism of AMP gene expression differs from that in Drosophila melanogaster, and we are further analyzing this finding.

In addition, the insect epidermis acts as a physical barrier against foreign invaders. We are trying to elucidate the role of the epidermis as a barrier by examining the effects of entomopathogenic fungi and insecticides on Coccinostomus infestans, whose epidermis formation has been suppressed by RNA interference methods.

Mechanism of insecticide resistance

　Many plants have evolved to synthesize and accumulate substances that are highly toxic to insects, making them less likely to be eaten by insects. On the other hand, insects have detoxification enzymes (for example, cytochrome P450) that rapidly convert such substances to less toxic substances when they are eaten. These enzymes also detoxify insecticides administered to insects. Although, when the same type of insecticide is repeatedly applied to the same field, pest populations that are resistant to the insecticide can emerge and cause a serious problem, it is reported that the presence and activity of detoxyfication enzymes increase in such pesticide-resistant pest populations.

　Therefore, we are currently conducting research focusing on the enzymes involved in insecticide detoxification and metabolism. We are investigating the involvement of detoxification enzymes in agricultural pests such as thrips, as well as the mechanisms underlying the development of drug resistance.

Red flour beetle (Tribolium castaneum) from wheat flour

Population of mealybugs (Planococcus kuraunhiae)

Planococcus kuraunhiae (Female)

Planococcus kuraunhiae (Male)

Chemical communication mechanisms in termites

Insects perceive chemicals, light, and sound (or vibration) to obtain information about their surroundings and to communicate with other individuals. Many insects use their olfaction and gustation to perceive chemicals in their environment for a variety of purposes including foraging, mating behavior, and searching for egg-laying substrates. In particular, social insects (ants, bees, termites, etc.) have developed a much more sophisticated chemical communication system than solitary insects. Within a colony of social insects, there are several groups of individuals that are behaviorally and morphologically specialized to perform a particular task, and these groups are called "castes". Each caste is engaged in caste-specific tasks, so the societies of social insects are based on division of labor.

Pheromones are chemical substances used for communication between organisms that innately elicit specific behavioral or physiological changes in other individuals of the same species. In our lab, we are exploring the evolutionary background that enabled termites to develop complex societies based on chemical communication by identifying the components and functions of termite pheromones and investigating the molecular mechanisms by which termites send and receive their pheromones, using mainly the Japanese subterranean termite (Reticulitermes speratus). Also, we aim to use the findings to develop termite control methods that reverse the behavioral characteristics of termites.

　For more information on the research results, please visit the Mitaka's website.

Antimicrobial compounds produced by termties

Termites and other social insects are at risk of spreading certain diseases in their nests because they form colonies of many blood-related individuals. Therefore, they produce and use a wide variety of antimicrobial substances to disinfect and sterilize their nests and inhibit the invasion, germination, and growth of any pathogenic microorganisms.

　We are identifying the components and functions of the antimicrobial substances used by termites and unraveling the mysteries of their colony-level quarantine strategy. Understanding this strategy will help us to better understand the effectiveness of biological controls against termites and their resistance to insecticidal ingredients, which will in turn inform our control methods.

For more information on the research results, please visit the Mitaka's website.

King, secondary queens, soldier, workers of Reticulitermes speratus

Functions of soldier pheromone in R. speratus

Antimicrobial agents secreted from R. speratus workers

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