Field experiments at Wytham, Oxon., UK conducted over 5 years (1993- 1998) examined the potential effects of various components of climate change on a grassland community, including predicted rises in the intensity and frequency of droughts. Drought stress reduced vegetation cover but had no effect on overall insect density, although there were changes in relative abundance of insect species over time. This study seeks a mechanistic understanding of the field responses.
Three dominant grasses from the field site were examined in the laboratory: Cock’s foot, Dactylis glomerata; Yorkshire fog, Holcus lanatus; False oat grass, Arrhenatherum elatius. Initial experiments were also conducted on barley, Hordeum vulgare. Plants were watered to saturation or subjected to a drought stress of -0.2MPa. The effects of drought stress on plant growth and on the performance of the grass feeding aphid Rhopalosiphum padi were studied. In all plant species, drought stress led to a reduction in the daily height increase and a reduced level of new leaf growth. On barley, Dactylis glomerata and Holcus lanatus, drought stress resulted in a reduction in aphid performance (lower intrinsic rate of increase). However, on Arrhenatherum elatius, aphid performance was not significantly altered by the drought treatment.
In an attempt to explain these results, the feeding behaviour of R. padi on well-watered and drought-stressed plants has been monitored using electrical penetration graph (EPG) techniques. However, no significant differences in the occurence or duration of feeding behaviour were found between the treatments in any of the plants studied.
Further work will involve the use of aphid stylectomy to collect phloem sap from the plants, which can be analysed for amino acid and sugar concentration and osmotic pressure, to determine if there is a nutritional basis for the differences observed in insect performance.
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA