Eco-evolutionary feedback to a pesticide worsens the impact of a pesticide switch in a pivotal freshwater non-target species

Pest management often requires the switches of insecticides, sequentially exposing non-target populations to different compounds. In a two-phased experiment, we assessed whether exposure to the pesticide chlorpyrifos induces rapid evolution in the non-target species Daphnia magna, and quantified the response of control and pre-exposed populations to a second exposure to the same pesticide, another pesticide with the same mode of action (malathion), or a pesticide with another mode of action (deltamethrin). Chlorpyrifos selection induced rapid shifts in genotype composition and reduced genotype richness, and strongly influenced population development following the second exposure. Chlorpyrifos-selected populations outperformed control populations when subsequently exposed to chlorpyrifos and malathion, but underperformed when exposed to deltamethrin. Our results highlight an eco-evolutionary feedback in which rapid adaptive responses to a pesticide worsens the response when exposed to a different type of pesticide in non-target species, increasing vulnerability to common agricultural practices.