Nothing lasts forever, including the effect of chemicals aimed to control pests in food production. As old pesticides have been compromised by emerging resistance, new ones have been introduced and turned the odds back in our favour. With time, however, some pests have developed multi-pesticide resistance, challenging our ability to control them. In salmonid aquaculture, the ectoparasitic salmon louse has developed resistance to most of the available delousing compounds. The discovery of genetic markers associated with resistance to organophosphates and pyrethroids made it possible for us to investigate simultaneous resistance to both compounds in approximately 2000 samples of salmon lice from throughout the North Atlantic in the years 2000–2016. We observed widespread and increasing multiresistance on the European side of the Atlantic, particularly in areas with intensive aquaculture. Multiresistant lice were also found on wild Atlantic salmon and sea trout, and also on farmed salmonid hosts in areas where delousing chemicals have not been used. In areas with intensive aquaculture, there are almost no lice left that are sensitive to both compounds. These results demonstrate the speed to which this parasite can develop widespread multiresistance, illustrating why the aquaculture industry has repeatedly lost the arms race with this highly problematic parasite.

没有什么是永恒的，包括旨在控制食品生产中害虫的化学品的影响。由于旧的农药因新出现的耐药性而受到损害，新的农药被引入并扭转了对我们有利的局面。然而，随着时间的推移，一些害虫已经产生了多种农药抗药性，对我们控制它们的能力提出了挑战。在鲑科鱼养殖中，外寄生鲑鱼虱已对大多数可用的除虱化合物产生了抗药性。与有机磷酸酯和拟除虫菊酯抗性相关的遗传标记的发现使我们能够同时研究 2000 年至 2016 年北大西洋各地约 2000 个鲑鱼虱样本对这两种化合物的抗性。我们在大西洋的欧洲一侧观察到广泛且不断增加的多重抗药性，特别是在集约化水产养殖地区。野生大西洋鲑鱼和海鳟鱼以及未使用除虱化学品地区的养殖鲑鱼宿主身上也发现了多重抗性虱子。在集约化水产养殖地区，几乎没有对这两种化合物敏感的虱子。这些结果证明了这种寄生虫产生广泛的多重抗药性的速度，说明了为什么水产养殖业在与这种高度问题的寄生虫的军备竞赛中屡屡失败。