The effect of simulated acid rain on the performance ofNeodiprion sertiferlarvae fed on treated Scots pine needles was tested in a subarctic area with low ambient pollution level. Acid rain treatments (pH 4 and pH 3, both with H2SO4and HNO3) did not significantly affect the relative growth rates or cocoon weights ofN. sertifer2 or 3 years after the start of the treatments. The relative growth rate ofN. sertiferlarvae was slightly (nonsignifi‐cantly) higher on plots receiving only ambient rain than on irrigated control plots. The quality of foliage before the start of the treatments explained a significant proportion of the variation in the performance ofN. sertiferlarvae in the bioassay conducted 3 years later.