APHID RESPONSES TO PLANT SURFACE FACTORS

Glen Powell¹, Sangita P. Manial², Jim Hardie¹and John A. Pickett^1
1Imperial College at Silwood Park, Ascot, SL5 7PY, UK.
²IACR-Rothamsted, Harpenden, AL5 2JQ, UK.

When aphids encounter a potential host, they walk across the plant surfaceand may insert their stylet mouthparts. The initiation of styletpenetration depends on the sensory assessment of a number of phylloplanefeatures, including colour, texture and phytochemicals (volatile and non-volatile). Video recording of the black bean aphid, Aphis fabae, showed thatthese oligophagous insects rapidly inserted their stylets following contactwith host plants (beans), but were reluctant to penetrate non-hosts (oats). However, when epicuticular waxes were removed from oats, using celluloseacetate, aphids penetrated the plant surface significantly earlier thanon oats with the wax layer intact. Chloroform extraction of epicuticularlipids, followed by GC-MS, revealed a complex blend of wax components onbeans, whereas one compound (hexacosanol) predominated on oats. Initiationof stylet penetration by A. fabae was delayed when the oat extract wasapplied to artificial surfaces. The results suggest that epicuticularlipids play an important role in the early stages of host plant selectionby A. fabae.