BACKGROUND The standard operating procedure for testing the susceptibility of adult mosquitoes to neonicotinoid or butenolide insecticides recommends using a vegetable oil ester (Mero) as a surfactant. However, there is growing evidence that this adjuvant contains surfactants that can enhance insecticide activity, mask resistance and bias the bioassay. METHODOLOGY/PRINCIPAL FINDINGS Using standard bioassays, we tested the effects of commercial formulations of vegetable oil-based surfactants similar to Mero on the activity of a spectrum of active ingredients including four neonicotinoids (acetamiprid, clothianidin, imidacloprid and thiamethoxam) and two pyrethroids (permethrin and deltamethrin). We found that three different brands of linseed oil soap used as cleaning products drastically enhanced neonicotinoid activity in Anopheles mosquitoes. At 1% (v/v), the surfactant reduced the median lethal concentration, LC50, of clothianidin more than 10-fold both in susceptible and in resistant populations of Anopheles gambiae. At 1% or 0.5% (v/v), linseed oil soap restored the susceptibility of adult mosquitoes fully to clothianidin, thiamethoxam and imidacloprid and partially to acetamiprid. By contrast, adding soap to the active ingredient did not significantly affect the level of resistance to permethrin or deltamethrin suggesting that vegetable oil-based surfactants specifically enhance the potency of some classes of insecticides. CONCLUSIONS/SIGNIFICANCE Our findings indicate that surfactants are not inert ingredients, and their use in susceptibility testing may jeopardize the ability to detect resistance. Further research is needed to evaluate the potential, the limitations and the challenges of using some surfactants as adjuvants to enhance the potency of some chemicals applied in mosquito control.

中文翻译：

---

植物油基表面活性剂是增强新烟碱类杀虫剂功效的佐剂，并且可能使成年蚊子的药敏试验产生偏差。

背景技术用于测试成年蚊子对新烟碱类或丁烯内酯杀虫剂敏感性的标准操作程序建议使用植物油酯(Mero)作为表面活性剂。然而，越来越多的证据表明，这种佐剂含有表面活性剂，可以增强杀虫剂活性、掩盖抗性并使生物测定产生偏差。方法/主要发现 使用标准生物测定法，我们测试了与 Mero 类似的植物油基表面活性剂商业配方对一系列活性成分活性的影响，包括四种新烟碱类杀虫剂（啶虫脒、噻虫胺、吡虫啉和噻虫嗪）和两种拟除虫菊酯（氯菊酯）和溴氰菊酯）。我们发现，用作清洁产品的三种不同品牌的亚麻籽油肥皂大大增强了按蚊的新烟碱活性。当浓度为 1% (v/v) 时，表面活性剂将噻虫胺在冈比亚按蚊易感群体和耐药群体中的中位致死浓度 LC50 降低了 10 倍以上。1% 或 0.5% (v/v) 的亚麻籽油皂完全恢复了成年蚊子对噻虫胺、噻虫嗪和吡虫啉的敏感性，部分恢复了对啶虫脒的敏感性。相比之下，在活性成分中添加肥皂并没有显着影响对氯菊酯或溴氰菊酯的抗性水平，这表明植物油基表面活性剂特别增强了某些类别杀虫剂的效力。结论/意义我们的研究结果表明表面活性剂不是惰性成分，它们在药敏试验中的使用可能会危及检测耐药性的能力。需要进一步的研究来评估使用某些表面活性剂作为佐剂来增强某些用于蚊子控制的化学品的效力的潜力、局限性和挑战。