The combination of electronic monitoring and video-assisted observations of plant penetration by aphids and behavioural effects of polygodial

Simultaneous electronic and close-up video recordings were made of behaviour during the initial 15 min of plant contact by adult, apterous Aphis fabae Scopoli on tick bean seedlings (Vicia faba Moench). Electronic techniques accurately determined stylet penetration of plant tissue and there was a close correlation between penetration and periods during which the insect antennae and body were immobile (r = 0.994, n = 60). Video techniques were then used alone to infer stylet penetration and the behaviour of aphids after various treatments was monitored. In particular, the time to first penetration, the number of penetrations, the mean duration of penetrations and the total time of penetration were observed. Behavioural differences were recorded between tethered (as required for electronic recording) and freelymoving insects as well as between fed and starved insects. The behaviour of starved aphids placed on beans treated with the plant-derived antifeedant, polygodial could not be distinguished from aphids on solvent-treated control beans. However, there were significant differences in behaviour of aphids which had previously been exposed to polygodial on plant or green/yellow paper surfaces for 24 h when compared with insects exposed to solvent alone. The possible modes of action of polygodial are discussed.