Entomologia Experimentalis et Applicata 74: 91-94, 1995. 91 ~) 1995 Kluwer Academic Publishers. Printed in Belgium. Short communication Responses of Myzuspersicae to the repellent polygodial in choice and no-choice video assays with young and mature leaf tissue Glen Powell l, Jim Hardie I & John A. Pickett 2 1AFRC Linked Research Group in Aphid Biology, Department of Biology, Imperial College at Silwood Park, Ascot, Berks, SL5 7PY, UK; 2AFRC Institute of Arable Crops Research, Rothamsted Experimental Station, Harpenden, Herts, AL5 2JQ, UK Accepted: April 5, 1994 Key words: aphid, antifeedant, contact chemoreception, discrimination, Myzus persicae, polygodial, video Introduction Polygodial is a plant-derived drimane sesquiterpenoid which shows antifeedant activity against aphids, and has been applied successfully in field trials, reducing cereal aphid numbers and consequently spread of bar- ley yellow dwarf virus (Dawson etal., 1986). When the compound was painted onto leaf halves for laboratory choice assays, significantly fewer numbers of aphids settled on these areas (Pickett et al., 1987; Asakawa et al., 1988). Polygodial can have a long term contact effect, affecting aphid behaviour after 24 h exposure on leaves or other green surfaces (Hardie et al., 1992; Powell et al., 1993). However, aphids can apparently detect the compound very rapidly, within 2 min of plant access, and video recordings of behaviour suggested that the repellency involves antennal tip contact with the polygodial-treated leaf area (Powell et al., 1993). Despite such clear demonstrations of repellency, when whole mature leaves (Griffiths et al., 1982) or seedlings (Hardie et al., 1992; Powell et al., 1993) were treated with polygodial, allowing no choice of a less deterrent substrate, aphids showed no differences in behaviour from those on control plants. No direct comparisons have been made of aphid responses to polygodial applied in choice and no-choice tests, with other experimental conditions held constant; such an approach may help interpret previous findings and con- tribute to a better understanding of the repellent effect. In this study, the behaviour of Myzus persicae (Sulzer) was video-recorded on polygodial- and solvent-treated leaf discs, in both choice and no-choice situations. As previous experiments have indicated that the aphid- repellent properties of polygodial may depend on leaf age, being more effective on mature leaves than on young cotyledons (Powell et al.. 1993), the experi- mental treatments were tested on discs cut from both young and mature leaves. Materials and methods An insecticide-susceptible clone of M. persicae (Pick- ett et al., 1987) was reared on Chinese cabbage (Bras- sica pekinensis L. cv. 'Tip Top') at 15 ~ and L16:D8 photoperiod. Adult apterous virginoparae were collect- ed and starved for 2-I-1 h before use. Aphid behaviour was examined on discs cut from either mature (fully expanded from 5-6 week old plants) or young (first leaf from 2 week old plants at 1-2 leaf stage) Chinese cabbage leaves. The upper surface of a leaf was either entirely painted with a 0.1% synthetic racemic mix- ture of (+)-polygodial or ethanol solvent (no-choice test), or half with polygodial and half with ethanol, on either side of the midrib (choice test). The solvent was allowed to evaporate completely, and a 16 mm diame- ter leaf disc was then cut, centrally across the midrib, and floated on water in a transparent dish (Fig. 1). The dish was positioned above a diffuse light source, a single aphid placed near the centre and movements