Contact with the host plant enhances aphid survival at low temperatures

1. The hypothesis, suggested by previous studies, that host plant contact reduces the cold tolerance of anholocyclic aphids was tested under laboratory conditions. Adult and first-instar Rhopalosiphum padi (L.) were exposed to temperatures of 0, -5 and -10 degrees C on intact plants, excised leaves and in the absence of contact with plant material. 2. Median lethal time (LT(50)) values at all three temperatures indicate that aphids exposed in association with plant material survive longer than aphids that have no contact with their host plant. The difference in survival was most pronounced at -10 degrees C. Therefore, the above hypothesis is rejected for aphids on cereals because host plant contact apparently enhances cold tolerance. 3. Exposure on excised leaves also enhanced aphid survival at low temperature but was less effective than the intact plant. This suggests that plant quality as well as the presence or absence of plants is important in the cold tolerance of aphids on cereals.