Division of Insect Sciences

Insect-Plant Interaction Research Unit

Analyses of the mechanisms of plant resistance to herbivorous insects and adaptive feeding in insects

 Plants have evolved chemical or physical features as resistance mechanisms to protect against the feeding damage caused by insects. On the other hand, herbivorous insects that overcome plant defenses have also evolved to be able to utilize the food plants. We are conducting fundamental research on these insect-plant interactions with a view for developing new insect-resistant crops and innovative sustainable methods for insectpest control. A primary study in our research unit focuses on the brown planthopper, Nilaparvata lugens, and the green leafhopper, Nephotettix cincticeps. These insects suck nutrient fl uids from sieve tubes of rice, Oryza sativa, and occasionally transfer the disease-causing microbes. We are trying to identify substances from the saliva or other body parts of the insects, which have key roles in the sucking procedure and in utilization of nutrients. We also are attempting to isolate insect-resistance genes from some rice strains. However, it is recognized that an insect “biotype” can arise which breaks the barrier of the resistant rice. Thus, it is also important to know the adaptive mechanisms of the insects overcoming the rice defense as well as the function of the resistance genes of rice. Our research covers defense mechanisms of various plant species and adaptive feeding strategies of herbivorous insects, such as identifying novel plant secondary metabolites and their functional effects on insect feeding, and clarifying mechanisms determining host-plant range that could cause appearance of novel insect pests for agricultural crops.

By using a current circuit conducting trough, a brown planthopper and a rice plant, different wave patterns of the current can be recorded depending on each stage of sucking process. Attainment of sucking fluids from the rice sieve tube could be observed in an insect feeding on the insect-sensitive rice strain but not the resistant one.

More than 20,000 plant species exude latex from the wounded site and the latex contains various plant secondary metabolites. For example, we identified that the latex exudate of mulberry leaves (arrows) contains sugarlike alkaloids, D-AB1 and DNJ, which inhibit sugar metabolism and digestion, and a novel protein, MLX56, which binds chitin; thus, they inhibit insect growth.