The extent to which perturbations are modulated and delayed in population systems is a question of considerable theoretical and practical interest. Organisms with a temporal refuge, for example insects with prolonged diapause, are likely to have strongly buffered populations with long response lags, but little is known concerning how disturbances are actually mediated in natural populations. We show experimentally that the gall midge Contarinia vincetoxici has a prolonged diapause with a “bank” in the soil where diapausing larvae can reside for at least six winters. This bank acts as a strong buffer against disturbance. We stopped recruitment to the larval bank during eight years by removing all new galls, but no significant effects on gall density were found. Response lags may thus be very long even in populations of apparently shortlived animals. Population fluctuations during the last decade were evidently largely determined by events taking place prior to this period.