Insecticide Resistance Study in Plutella xylostella L. X. The IGR-resistance and the possible management strategy

Abstract

The benzoylphenyl urea-type insect growth regulators (IGRs) have caused the newest type of resistance in diamondback moth (DBM, Plutella xylos-tella). The possible mechanism, the declining rate, the genetics and the possible management strategy of this resistance have been investigated. The results indicated that DBM can develop IGR-resistance up to thousand folds in less than one and half years or equal to 30 generations in field, and this resistance is attributed to the metabolic degradation by a new mixed function oxidase (mfo) in DBM induced from the intensive IGR sprays. The resistance can only be maintained by continuous IGR selection, or it will decline when the selection pressure was lift. The decline of IGR-resistance can be accelerated by crossing the susceptible strain with the resistant population, and by such a simple manipulation, greater reduction in resistance was accomplished than the addition of synergist, piperonyl butoxide. Genetically, the IGR-resistance is not sex-linked and is highly recessive, and has not been confirmed as the monofactorial control. When the susceptible gene for IGR was re-introduced into the resistant population, this genetical dominance can self-propagate as the generations proceed. In a few generations, the whole population will restore the high sensitivity to IGRs, which was similar to the susceptible strain. By establishing sanctuary in the field to harbor a portion of DBM population free from the IGR selection, the dominant susceptible gene or genes will be preserved in the field DBM to delay or prevent the development of IGR-resistance. This strategy can be utilized in intensively cultured vegetable areas where small areas are kept free from IGRS to serve as the sanctuary for IGR-susceptible DBM. 本省自1987年起，大量使用新登記之昆蟲生長調節劑（Insect Growth Regulator, IGR）防治小菜蛾以來，雖在田間僅使用一年半（相當於30個小菜蛾世代），即已遭逢高達千倍之抗藥性。針對此一問題進行的研究得知，其抗藥性之機制為一新誘發之氧化代謝酶，添加協力劑piperonyl butoxide（pb），可使此抗性之幅度下降。利用遺傳雜交試驗顯示，此一IGR之抗性無「性連遺傳」關係，且係隱性基因，利用雜交、回交及自交分析，皆未能得到與單基因控制理論相符合之結果，但此抗性主要為隱性基因控制之事實已可確認。敏感品系在遺傳上具有顯性之優勢，將抗性族羣與感性族羣進行一次雜交即可造成IGR抗性之大幅下降，其幅度甚至超過添加協力劑之效果。雜交後再任其自交3─4代，全族羣對IGR之感度即已恢復，而與感性品系相當。引入感性品系對該抗性族羣之抗性下降幅度及速度均有促進之作用，此一特質可在未來之IGR抗性管理策略上加以應用，如保留部份間雜蔬菜區僅使用蘇力菌防治，以便在田間保護部份小菜蛾族羣不受IGR選汰，藉以保存在遺傳上占優勢之IGR敏感因子，可以自然雜交之方式延遲或阻止IGR抗藥性之發生。