In collaboration with the National Agriculture and Food Research Organization, the researchers have elucidated that only several times of use of an insecticide causes accumulation of insecticide-degrading bacteria in the soil, and insecticide resistance can develop rapidly in the pest Riptortus pedestris, when the pest acquires the insecticide-degrading bacteria from the soil.

Dynamics of insecticide-degrading bacteria in the soil and the gut of pests under repeated spraying of insecticide

The appearance of pests, on which insecticides no longer work due to their long-term use, has become a major problem worldwide. Once insecticide resistance of pests develops, such previously-used insecticides become less effective. Since it takes much time to develop a novel insecticide, insecticide resistance can cause serious damage to human society by feeding on crops. To prevent the development of insecticide resistance more efficiently, the elucidation of mechanisms of insecticide resistance development is demanded.

The researchers sprayed the recommended amount of an insecticide weekly to soil and measured the density of insecticide-degrading bacteria, which belong to the genus Burkholderia, in the soil. At the same time, they reared the soybean pest Riptortus pedestris on the treated soil and investigated the infection rate with insecticide-degrading bacteria. As a result, pests infected with insecticide-degrading bacteria emerged only after two-times spraying. The results of this research demonstrated that insecticide resistance could develop rapidly in just several weeks. The same tendency was observed in the field environment.

The researchers will perform microscopic analyses, including investigation of the molecular mechanism of detoxication by insecticide-degrading bacteria in Riptortus pedestris, to gain a comprehensive understanding of the development of insecticide resistance by symbiotic bacteria in insect pests.