Interactions between plant odours and pheromone reception were studied in small ermine moths ( Yponomeuta spp.) with electroantennogram and single cell recordings, both separately and simultaneously. The results verified that interactions do indeed occur at the receptor level. It is suggested that, in the reproductive isolation of these moths, plant odours may play both a direct role through plant odour receptors and an indirect role via modulation of pheromone receptors.