TARSAL CONTACT CHEMORECEPTOR FOR THE HOST MARKING PHEROMONE OF THE CHERRY FRUIT-FLY, RHAGOLETIS-CERASI - RESPONSES TO NATURAL AND SYNTHETICCOMPOUNDS

The European cherry fruit fly (Rhagoletis cerasi L.; Diptera, Tephriti dae) marks cherries (Prunus avium L.) after oviposition with a host ma rking pheromone (HMP). The marking trail prevents additional ovipositi on by the same or other females into the same fruit. On the ventral si de of the tarsi of both sexes, contact-chemoreceptor sensilla were ide ntified which contain a receptor cell selectively sensitive to HMP. Th e HMP receptors of males were slightly more sensitive than those of fe males, suggesting that the more general term 'host-marking pheromone' is more appropriate than the previously used 'oviposition deterring ph eromone (ODP)'. The four structural isomers of the HMP, glucopyranosyl )-oxy-8RS-hydroxypalmitoyl)-taurine, and various derivatives were synt hesized and tested in an electrophysiological bioassay. Both the 8R,15 R and the 8S,15R isomers of the HMP were equally active with a thresho ld of about 2 x 10(-10) M, and were shown to be present in the female faeces in similar proportions. The two 15S HMP isomers were about 13 t imes less active. Testing synthetic derivatives of the HMP molecule re vealed that the presence of the four moieties of the molecule are impo rtant for the activity: taurine, palmitic acid, C(8) hydroxyl group, a nd glucose (C(15)). The chain length of the fatty acid, the hydroxyl g roup at C(8) and the position of glucose at C(15) also influenced the activity. Only minor loss of activity (factor 2) relative to the natur al molecule was observed when the methyl group in the C(15) position w as removed. The removal of the beta-glycosidically linked glucose (rep laced by a hydroxyl group) resulted in about a 4-fold loss of activity . The cation of the HMP molecule seemed to have no effect on its activ ity, whereas both low and high pH reduced it significantly. Based on t hese results, field experiments have been initiated to control oviposi tion by cherry fruit flies on cherries applying the 15-desmethyl-HMP d erivative.