Division of Insect Sciences

Insect-Microbe Research Unit

Functional analysis of insect-associated microorganisms and viruses

Insects are the most diversified group in the animal kingdom. Various microorganisms including viruses infect insects and affect agricultural production. Our goal is to understand the interactions between insects and microorganisms and to integrate the knowledge in pest management strategies.
 Bucillus thuringiensis, a species of entomopathogenic bacteria, is known for a source of Bt toxins which are widely used for microbial pesticides and Bt crops. However, development of insect resistance threatens continued success of the utilization of Bt toxins. Understanding the mechanism of the insect resistance to Bt toxins is important to plan strategies against the resistant insects. We are identifying lepidopteran resistance genes for Bt toxins. The brown planthopper, Nilaparvata lugens, is one of the most destructive pests for rice. This insect not only causes severe sucking damage, but also transmits phytopathogenic viruses. We intend to find crucial components for the virus transmission in insect vectors to facilitate the next stage of research for plant virus-insect vector interactions.
 Some maternally-transmitted symbiotic bacteria can subtly manipulate the reproductive systems (including sex determination) of their host insects for their own benefit. Understanding the mechanism of this striking ability of such bacteria may allow us to develop a novel strategy to regulate demography of pest insects.

A reovirus replicating in the salivary gland of the brown plant hopper, Nilaparvata lugens

(a) The location of salivary glands (marked by green spots) in the brown plant hopper
(b) Immunohistochemical detection of reoviruses in a thin section of a salivary gland
(c) Electron microphotograph of multiplicated reoviruses in salivary gland of the insect

Anomala cuprea (Coleoptera) larvae infected with an entomopoxvirus show the symptoms of the infection such as a whitish appearance and underdevelopment (left, infected larva; right, healthy one).

Gonadal abnormalities induced by the suppression of Wolbachia population

In the butterfly Eurema mandarina, males are feminized by Wolbachia. Suppression of the Wolbachia density during larval development results in generation of intersexes (i.e., individuals having both male and female characters). (a) Normal male; (b) Normal female; (c) Intersex