Point

We have elucidated that only several-time use of a 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

Background

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 and by spreading infectious disease. To prevent the development of insecticide resistance more efficiently, the elucidation of mechanisms for insecticide resistance is demanded.

Outcomes and Methods

We sprayed insecticide weekly to soil and measured the density of insecticide-degrading bacteria, which taxonomically belong to the genus Burkholderia, in the soil. At the same time, we reared a 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 (i.e. 2 weeks) with the recommended amount of insecticide, and after six-times spraying (i.e. 6 weeks), approximately 90 % of pests had been infected with insecticide-degrading bacteria. Previously, it was thought that insecticide resistance in pests due to repeated use of insecticides would develop at the population level through genetic changes in the pest insects themselves after several years or several decades. However, the results of our research demonstrated that such insecticide resistance could develop rapidly in just several weeks through symbiosis with insecticide-degrading soil bacteria.

Future Plan

We hope to apply this research into development of an pest control technique based on risk assessment by estimation of occurrence probability of insecticide resistant via monitoring the density of insecticide-degrading bacteria in the soil.