LONG,LATERAL SHORT, MEDIAL SENSILLA SENSILLA Z7-~2:OAc -- ~ Z5-14,OAc I Z11-14,OAc Z7-14:OAc Z9-14'OAc I'-- 100 + -i--1 o~ 50 s0 1oo +o Fig. 2. Frequency of receptor cells in lateral (long) and medial (short) sensilla on anten- nae of male A. exclamationis specifically re- sponding to pheromone components and three related chemica|s (n = 50 for each sen- sillum type). For experimental details see text common one responded mainly to Z9- 14:OAc, a second type to Z7+ 14: OAc with a weak response also to Z9- 14:OAc, and a third type responded exclusively to Z11-14: OAc (Fig. 2). The medial shorter sensilla towards the antennal axis have two cells: Cell A with a high spike amplitude and cell B with a low spike amplitude. The A cell responds to totally different phero- mone components than the cells in the marginal long sensilla: the majority (82%) responds to Z5-14: OAc, where- as a lower number (18%) is activated exclusively by Z7-12:OAc (Fig. 2). The function of the B cell is still un- known. It did not respond to any of the compounds tested. These results were corroborated by measuring the re- sponse of ten short sensilla to the same compounds with the penetration tech- nique [81. The receptor types found by us are thus in agreement with what Priesner re- ported [6]. The proportion of sensilla- containing cells sensitive to compounds other than Z5- and Z9-14:OAc is striking. Trapping experiments by Priesner [6] showed that these other compounds have an inhibitory effect on the attraction of male A. exctarna- tionis. Our own unpublished gas chro- matographic analyses on capillary col- umns did not reveal traces of any of them in female extracts (<0.5% of Z5 14:OAc). They are, thus, most probably pheromone compounds in some other competing species. More interestingly, however, we found a clearcut correlation between the mor- phology of individual sensilla, their spatial localization, and their sensitivi- ty to different compounds. The recep- tors for the pheromone component zg-14:OAc are exclusively arranged along the lateral margins of the anten- nal segments, and are each innervated by one neuron. The Z 5-14:OAc recep- tors are all placed medially in sensilla containing also a second cell. Such a spatial arrangement of receptors sensi- tive to different pheromone compo- nents has not been reported before. It is interesting to note that Z9- 14: OAc is perceived by a specific cell in the long distal sensilla placed on the edge of the male A. exclarnationis an- tennal segments. There is in the phero- mone blend an optimal proportion of this component to Z5-14: OAc of less than 10% for male attraction. The pro- portion of molecules perceived by the sensilla from the air is by aerodynamic laws much higher for distal sensilla than for central ones [9]. This means that the localization of the Z9-t4: OAc receptors on the male A. exclamationis antenna could be adaptive for sensitive detection of the minor one of the two pheromone components. Received November 25, 1985 and January 10, 1986 1. Altner, H., in: Olfaction and Taste, Vol. VI, p. 351 (eds. Le Magnen, J., MacLeod, P.). Information Retrieval 1971 2. Priesner, E., in: Chemical Ecology, p. 57 (ed. Ritter, F.J.). Amsterdam: Elsevier 1978 3. Van Der Pers, J.N.C., Ltfstedt, C., in: Mechanisms in Insect Olfaction (eds. Payne, T., Birch, M., Kennedy, C.). Ox- ford Univ. Press (in press) 4. Bestmann, H.J., et al.: Tetrahedron Lett. 2I, 747 (1980) 5. Vrkoc, J., Konyukhov, V.P., Kovalev, B.G.: Acta ent. bohemoslov. 80, 184 (1983) 6. Priesner, E.: Z. Naturforsch. 40c, 943 (1985) 7. Van Der Pers, J.N.C., den Otter, C.J.: J. Insect. Physiol. 24, 337 (1978) 8. Hubel, D.H: Science 125, 549 (1956) 9. Kanaujia, S., Kaissling, K.E. : J. Insect. Physiol. 31, 71 (1985) 10. Hallberg, E.: Cell Tiss. Res. 218, 209 (1981) Dosage Response to Ethanol Mediates Host Selection by "Secondary" Bark Beetles D. Klimetzek, J. Kthler, J.P. Vit6 and U. Kohnle Forstzoologisches Institut der Universitfit, D-7800 Freiburg/Br. We report a unique dosage response pattern in which ethanol affects aggre- gation of scolytids (Coleoptera: Scoty- tidae) on host trees: High ethanol con- centrations enhance the response of nonaggressive (" secondary") bark bee- tles and ambrosia beetles, but interfere with the pheromone response among aggressive species. Species depending on fresh host material but unable to infest live trees show an intermediate response pattern: a low ethanol con- centration increases, high concentra- tion reduces attraction to host odors and/or pheromonal compounds. Ethanol generates naturally by anaero- bic fermentation in the moist phloem and sapwood of logs, stumps or dis- eased trees [1], presenting temporary habitats for numerous insects. Con- flicting reports on the role of ethano! in bark beetle aggregation and/or host colonization [2, 14, 17] led us to inves- tigate the effects of ethanol concentra- tions on the response of four bark bee- tles (Ips typographus [L.], Leperisinus varius [F.], Itylurgops patliatus [Gytl.], Tomicus piniperda [L.]) and four am- brosia beetles (Trypodendron lineatum [Oliv.], Xyleborus dispar [F.], Xylebo- rus saxeseni [Ratz.], Xylosandrus ger- marius [Blandf.]) to traps baited with their respective pheromones and/or ethanol. Included was also a woodbor- ing l~Tnexilonid, Hylecoetus dermes- toides L. Field tests were conduced near Frei- burg/Br, using commercial flight bar- rier traps (R6chling, Haren/Ems, FRG) spaced approx. 15 m apart in la- tin square design. Ethanol of different concentrations was eluted from 0.05 mm low-density polyethylene bag dispensers (7 x 10 cm) or glass vials of different size to give a wide range of release rates (0.5-250 mg h -1 as esti- mated in the laboratory resp. 0.1-0.001 mg h -1 by using tenfold di- 270 Naturwissenschaften 73 (1986) Springer-Verlag 1986