Plant odours influence the host finding behaviour of apple psyllids (Cacopsylla picta; C. melanoneura)

The apple proliferation (AP) is an economically important plant disease which is caused by phytoplasmas. Because this disease is difficult to control, the management of the insect vectors responsible for the transmission of the AP phytoplasma, the phloem-feeding psyllids Cacopsylla picta and C. melanoneura (Homoptera: Psyllidae), could be the most promising strategy. The aim of this study is to find chemical components which influence the migration behaviour of apple psyllids in summer and after winter, respectively. Up to now, less is known about the chemical signals which are used by apple psyllids to distinguish between their host and non-host plants and between their summer- and winter-hosts. The responses of two psyllid species occurring on apple trees (Cacopsylla picta and C. melanoneura) to leaf odours of different plant species were investigated using a static four-chamber olfactometer. The first results are presented here: During spring, the polyphagous C. melanoneura clearly preferred its summer-host plants odours (apple, hawthorn) to a non-host plant odour (cherry), and hawthorn to apple odour. After reproduction in spring, the new generations of both psyllid species leave their hosts plants in early summer and switch to at least partially unknown host plants, maybe conifers, where they will spend the winter. During this migration period, the oligophagous C. picta prefer the odours of spruce and pine to the odour of its summer host plant apple, while the polyphagous C. melanoneura showed neither a preference for apple/hawthorn odours nor coniferous odours.