Behavioural thermoregulation in Acyrthosiphon pisum (Homoptera : Aphididae): the effect of parasitism by Aphidius ervi (Hymenoptera : Braconidae)

The effects of parasitisation by Aphidius ervi on the thermoregulatory beha viour of the pea aphid Acyrtosiphon pisum were studied in alfalfa fields an d in an experimental thermal gradient. In the field, mummies were found exc lusively on the adaxial surface of the upper leaves, and aphids in the mid canopy. The adaxial surface of the upper leaves was ca, 2 degreesC hotter t hat the mid-canopy, In the thermal gradient, the thermal effect (selected m inus exposure temperature) was higher in magnitude in non-parasitised than in parasitised aphids; the thermal effects of both types of aphids were lin early and negatively correlated with exposure temperature (i.e. aphids show ed negative thermal sensitivity), The thermal sensitivity of parasitised ap hids was lower than that of non-parasitised aphids. The results are discuss ed in relation to hypotheses on factors governing the host-parasite relatio nship. (C) 2001 Elsevier Science Ltd. All rights reserved.