Reduzierung der Eiablage von C. ohridella (Deschka & Dimic) durch Repellents

Bioassays in laboratory showed that leaves of A. hippocastanum mined by C. ohridella larvae are less attractive for landing of the insect than green ones. Further on, field examinations established a correlation between reduced oviposition on horse chestnut leaves and increased degree of leaf browning caused by mine action of larvae. Leaves browned by the mining grub are less attractive for C. ohridella adults than healthy ones. In order to use this mechanism in a control strategy, odour samples of healthy and various highly browned leaves caused by mining grub were taken from A. hippocastanum trees. The CLSA method (BOLAND et al., 1984) was utilised for collection of odour samples. The samples were analysed using the GC-MS/EAD method (WEISSBECKER et al., 2004) and single odour compounds were measured on insect's antenna via dilution series (1*10 -7 to 1*10 -2 , SCHUTZ et al., 1999). The experiments showed that more than 30 compounds are detectable by the olfactory system of the insect and that mining action of larvae induces a high alternation in leaf odour pattern of A. hippocastanum. The influence of the single compounds on C. ohridella oviposition was subsequently tested in laboratory bioassays. For that purpose, two healthy twigs of horse chestnut trees were offered to the moths. One of the twigs served as control, the other one was treated with the compound to be tested. By dint of the bioassays repellent compounds could be identified that reduce oviposition up to 50%. Cooperation partners for testing the compounds in field studies are being sought after. The single odorant compounds can be also tested as mixtures on adequate support on trees. Furthermore, the repellents should be combined with other alternative control methods like attractants (pheromones SVATOS et al., 1999 and kairomones AMCHER-SCHOON et al., 2002; KALINOVA et al., 2002; SCHWAB, 2003), removal of autumn leaf litter (MARX, 1997; GILBERT et al. 2003; PAVAN et al., 2003; BARANIAK et al., 2004) and/or promotion of natural enemies (GRABENWEGER et al., 2005; KEHRLI et al., 2005). The identification of repellent compounds offers the possibility of an extended alternative control strategy of C. ohridella. In field experiments the effectiveness of oviposition reduction using combined alternative methods on the reduction of leaf browning degree by complete larva development should be checked. The total tree browning should be delayed up to the natural browning in autumn without insecticide application, so that no aesthetic damage is caused in the cities (BALDER, 2003). Remarks If you are interested in commercialisation of the repellent method, please contact Mr. Dr. VOIGT (avoigt@science bridge.de) of the technology transfer organisation MBM Science Bridge GmbH of the Georg-August-University Goettingen. Ms. JOHNE accepts gladly scientific questions (bjohne@gwdg.de). A. BETTINA JOHNE was financially supported by evangelisches Studienwerk " e.V. Villigst".