Synergistic action of pesticide mixtures using glutathione-s-transferase- and esterase-inhibiting properties in diamondback moth (Plutella xylostella L.)

In vitro inhibitory activity of 34 insecticides and 31 fungicides to glutathione-S-transferase and esterases extracted from rats was determined. Of tested pesticides, the pesticides with high activity on both detoxifying enzymes were mixed with pesticides that are known to be detoxified by detoxifying enzymes. Glutathione-S-transferase was inhibited by thiodicarb $(I_{50}:1.87\times10^{-4}M)$, thiocyclam $(7.40\times10^{-4}M)$, dithianon $(7.55\times10^{-5}M)$, and tolylfluanide $(8.66\times10^{-5}M)$, while esterases by dichlorvos $(8.95\times10^{-8}M)$, pirimicarb $(2.74\times10^{-6}M)$, pyrazophos $(3.31\times10^{-5}M)$, and benomyl $(4.96\times10^{-5}M)$. After acephate known to be detoxified by glutathione-S-transferase was mixed with glutathione-S-transferase-inhibiting pesticides and phenthoate known to be detoxified by esterases was mixed with esterases-inhibiting pesticides, insecticidal activities of such mixtures were determined against diamondback moth (PlutelLa xylostella L.). Synergistic action was observed in all pesticide combinations. The highest synergistic action was obtained when phenthoate was combined with dichlorvos, showing that co-toxicity coefficients were 1512 and 1877 after 24 and 48 hours of treatment, respectively. Several other combinations of pesticides, such as phenthoate with benomyl, and acephate with dithianon, also showed synergism, showing that their co-toxicity coefficients were about 1,000 and 500, after 24 hours of treatment, respectively. Our results showed that combinations of pesticides inhibited by detoxifying enzymes and ones detoxified by detoxifying enzymes resulted in increased toxicities of pesticides, suggesting that such combinations could be used to develop pesticide mixtures with more broad spectrum and high effectiveness.

Glutathione-S-transferase와 esterase 효소 저해특성을 이용한 농약의 혼합 상승효과

본 연구는 다양한 계열의 농약을 대상으로 체내에서 농약을 무독화하는 효소로 알려진 glutathione-S-transferase(GST) 와 esterases 에 대한 저해정도를 조사하고, 이 중 저해력이 높은 약제를 선발하여 무독화 효소에 의하여 분해되는 것으로 보고된 약제와 혼합 처리하였을 때 나타나는 약효의 변화를 조사하고자 수행하였다. 무독화효소를 저해하는 농약을 선발하기 위하여 34종의 살충제와 31종의 살균제를 대상으로 glutathione-S-transferase와 esterases 에 대한 저해력을 측정한 결과, thiodicarb $(I_{50}:1.87{\times}10^{-4}M)$, thiocyclarn $(I_{50}:7.40{\times}10^{-4}M)$, dithianon $(I_{50}:7.55{\times}10^{-5}M)$, tolylfluanide $(I_{50}:8.66{\times}10^{-5}M)$은 glutathione-S-transferase의 활성을 강게 저해하였고, dichlorvos $(I_{50}:8.95{\times}10^{-8}M)$, pirimicarb $(I_{50}:2.74{\times}10^{-6}M)$, pyrazophos $(I_{50}:3.31{\times}10^{-5}M)$, benomyl $(I_{50}:4.96{\times}10^{-5}M)$은 esterases의 활성을 강하게 저해하였다. Glutathione-S-transferase를 저해하였던 thiodicarb, thiocyclarn, dithianon, tolylfluanide와 glutathione-S-transferase 에 의해 대사되는 것으로 알려진 aeephate를 혼합 (1:1)하여 배추좀나방 (Plutella xylostella L.) 에 처리하고 약효를 관찰한 결과, 각각의 단제를 처리하였을 때보다 약효가 상승되었다. 특히 dithianon과 thiocyclam을 acephate 와 혼합시 각각 7배와 4배 약효가 상승하였다. 그리고 esterase를 저해한 약제인 dichlorvos, pirimicarb, pyrazophos, benomyl 을 esterase 에 의해 대사되는 것으로 알려진 phenthoate 와 혼합하였을 경우에도 단제 처리시의 약효보다는 혼합처리시의 약효가 높았다. Phenthoate와 dichlorvos 혼합시 18배, phenthoate 와 benomyl 혼합처리시 12배의 약효상승효과가 나타났다. 본 연구의 결과들은 무독화과정 효소에 의해 무독화되는 약제를 무독화효소 저해제와 혼합처리시 약효상승이 유발된다는 것을 나타내는데, 이러한 결과들은 향후 혼합제 개발에 유용하게 사용될 수 있을 것이라 생각된다.