Insecticide Resistance Study in Plutella xylostella (L.)－VIII. The Specificity of Oxidative Detoxication Mechanism in Larval Stage

Abstract

In this study, we have observed that the resistance of DBM to organophosphorus insecticides are not associated with MFOs, and the natural declining rate of organophosphorus-resistance is closely correlated with the resistance level of different compounds in the field. Mevinphos, phenthoate, and methidathion are three organophosphorus insecticides with the fastest resistance declining rate, and also meet minimum resistance problem in the field On the other hand, methamidophos, mephosfolan, and diethguinalphion have the slowest rate and also met with enormous resistance in the field. Synthetic pyrethroids and carbamates are chiefly detoxicated by MFOs in DBM. By using separate DBM strains and with the help of piperionyl butoxide and other synergists, we have concluded that DBM can develop three separate MFOs for (1) synthetic pyrethroids, (2) carbofuran, and (3) carbaryl, propoxur, and methomyl. It seems that the cross resistance is not existed among three MFOs sub-systems. The evidences are present in Tables and discussed in the text. 本研究之目的在於測定小菜蛾幼蟲體內氧化解毒酵素對各類殺蟲劑之專屬性，以探討是否與抗藥性有關。以不同地區採得之感性及抗性小菜蛾為材料，除比較不同殺蟲劑之感度，折算成抗性比率外；並觀察抗性小菜蛾不再接觸農藥後，抗藥性下降的情形。另一方面，利用氧化解毒酵素之抑制劑（就毒效而言為協力劑，如 piperionyl butoxide），測定對各種殺蟲劑的協力程度，以決定氧化酵素對該殺蟲劑抗性所扮演之角色及其比重。結果發現有機磷類殺蟲劑受氧化解毒酵素影響甚小，與其抗藥性幾乎無關；但在試驗中發現小菜蛾幼蟲對美文松、賽達松及滅大松之抗性消退甚快，而對拜裕松、達馬松及美福松之抗性消退極慢，此一現象正好與該等藥劑在田間小菜蛾之抗性高低相吻合。影響抗藥性消退速率的原因，目前尚不清楚，小菜蛾對有機磷之抗性程度一向不及對氨基甲酸鹽或合成除蟲菊精劑，可能是與氧化解毒酵素無關之故。就合成除蟲菊精類殺蟲劑而言，3 種供試藥劑幾乎有相同之抗性消退速率，經過 6 代以後，抗性消退至原來抗性1/10；雖然其抗性消退速率甚快，但在田間之抗性極高，可能係氧化解毒酵素之誘發與消退均極為迅速。使用協力劑測定時發現，氧化解毒酵素為合成除蟲菊精類殺蟲劑抗藥性之主要機制，使用協力劑可使抗性小菜蛾恢復對除蟲菊精類殺蟲劑之敏感度，數種合成除蟲菊精類在此試驗中之表現均極一致，但仍有少部份之除蟲菊精抗性與氧化解毒酵素無關，是否來自酯酶，則有待進一步之求證。氨基甲酸鹽類殺蟲劑之測定結果發現：加保扶之毒理作用較特殊，與加保利、安丹及納乃得有差別。感性品系小菜蛾之氧化解毒酵素可以解去加保利、安丹及納乃得之毒性作用，然卻無法消除合成除蟲菊精之致毒能力，亦無法對加保扶發生解毒作用，可能為氧化解毒酵素之另一支。小菜蛾亦能對加保扶產生極高之抗藥性，且該抗藥性與其他氨基甲酸鹽類或合成除蟲菊精劑均無交互抗性，但 piperionyl butoxide 可以消除此一抗藥能力。由此判斷，小菜蛾之氧化解毒系統可能分別對（1）合成除蟲菊精類，（2）加保扶及（3）其他三個氨基甲酸鹽類，形成三個獨立的解毒系統，而其間可能不具有交互抗性關係。