Year 2 PhD: Effect of Drought on Plant/Aphid Interaction
After completing some preliminary experiments on wheat & Metopolophium dirhodum as well as sycamore & Drepanosiphum platanoides; I am preparing for a different approach. The development of complex drought range systems have been distracting from the investigation of any interaction effect, so I have decided to pare the next experiment down. I will be looking at six different plant species from three families and comparing their response to drought and the same aphid species: Myzus persicae.
I will also continue work on the Sycamore field site and the aphid Drepanosiphum platanoides. A rainout system of tarpaulin covered tunnels will prevent rainfall reaching the primary root system of 3 year old saplings. Controls with no tunnel and permeable tunnels will be used for comparison in a factorial experiment.
Year 1 PhD: Effect of Drought on Plant/Aphid Interaction
A gardener’s nightmare: aphids. With representatives feeding on the phloem sap of most plant groups, aphids are a ubiquitous pest. In temperate regions, one plant species in four is infested with aphids (Dixon, 1998).
Affected plants suffer mechanical damage when the aphid feeding stylet penetrates deep down into the phloem sap. Once established, phloem pressures of 1.5-3.0 MPa force sap up through the stylet (Dixon, 1998). Valuable nutrients are intercepted and part of the phloem stream diverted (Girousse et al., 2003) to their feeding site.
Although the aphid/plant interaction has been quite well studied, results are inconclusive and vary from species to species. This may be the result of interspecific variation (Oswald & Brewer, 1997), or disparate experimental method (Hoover & Newman, 2004).
Moreover, the response of the system to stress is complex and no united opinion has been formed. Research is most often focused on the ‘plant-stress hypothesis’ originally formulated by (Rhoades, 1983; White, 1984), yet few studies can confirm the idea, even with the sap-feeding insects it was based upon.
I am currently working on reading and identifying some of the key areas I would like to investigate. Of particular interest are:
Dixon, A.F.G. (1998) Aphid Ecology, Second edn. Chapman and Hall, London.
Eastop, V.F. (1973). Deductions from the present day host plants of aphids and related insects. In Insect/Plant Relationships (ed H.F. Vanemden), pp. 157-78. Blackwell Scientific Publications, Oxford.
Girousse, C., Faucher, M., Kleinpeter, C. & Bonnemain, J.-L. (2003) Dissection of the effects of the aphid Acyrthosiphon pisum feeding on assimilate partitioning in Medicago sativa. New Phytologist, 157(1), 83-92.
Hoover, J.K. & Newman, J.A. (2004) Tritrophic interactions in the context of climate change: a model of grasses, cereal Aphids and their parasitoids. Global Change Biology, 10(7), 1197-208.
Larsson, S. (1989) Stressful Times for the Plant Stress - Insect Performance Hypothesis. Oikos, 56(2), 277-83.
Oswald, C.J. & Brewer, M.J. (1997) Aphid-barley interactions mediated by water stress and barley resistance to Russian wheat aphid (Homoptera: Aphididae). Environmental Entomology, 26(3), 591-602.
Rhoades, D.F. (1983). Herbivore Population Dynamics and Plant Chemistry. In Variable Plants and Herbivores in Natural and Managed Systems (eds R.F. Denno & M.S. McClure), pp. 155-220. Academic Press Limited, London.
White, T.C.R. (1984) The Abundance of Invertebrate Herbivores in Relation to the Availability of Nitrogen in Stressed Food Plants. Oecologia, 63(1), 90-105.