IP Endocrinology

Identification of female and male sex pheromones in the solitary bee Osmia rufa (Hymenoptera: Megachilidae)

M. Ayasse¹, G. Dutzler¹, F. Schiestl¹, F. Ibarra² & W. Francke²

¹Inst. of Zoology, Althanstrasse 14, 1090 Vienna, Austria; ²Inst. of Organic Chemistry and Biochemistry, University of Hamburg, D-20146 Hamburg, Germany

The reproductive biology of the solitary bee Osmia rufa has been well studied, in order to investigate this species’ potential for crop pollination. Almost no data exist so far on the chemical communication involved in the mating biology. Males search for receptive females at feeding areas and nests. Most females of this monandrous species mate immediately after having emerged. Therefore, it should be an advantage for males to distinguish between receptive and unreceptive females. Males show a characteristic post-copulatory behaviour of rubbing the female wing surfaces with their sternites, which leads to the hypothesis that they mark the females with an antiaphrodisiac. In behavioural experiments, combined gas chromatography - electroantennography recordings (GC-EAD) and chemical analyses, we studied the function of female and male pheromones in mating biology. Bioassays with different samples obtained from attractive females showed extracts of the cuticular surface to be most attractive, indicating that the female sex pheromone is evidently located there. In GC-EAD analyses of surface extracts, we found that fatty acids, ethyl esters, hydrocarbons and aldehydes triggered receptor potentials in the antennae of males. Odourless dummy bees impregnated with synthetic compounds mixed according to the proportions found on the cuticular surface of unmated females were significantly more attractive to males than dummies impregnated with solvent only. In bioassays, O. rufa males clearly distinguished between newly emerged females and those that mated one or two days prior to a dual-choice experiment. Chemical analyses showed different odour bouquets of unmated and mated females and the total amount of odour decreased within three days after mating. The assumption that males mark females during copulation with an antiaphrodisiac, that is produced in the sternal glands, was confirmed by means of behavioural experiments, GC-EAD analyses and chemical analyses. Solvent extracts of wings obtained from just mated females yielded an increase of the total amount of odour as compared to that of unmated females and many of the main chemical compounds identified in the male sternal glands contributed to this increase. In dual-choice experiments, unmated females impregnated with sternal gland extracts proved significantly less attractive than females impregnated with solvent only. In a further bioassay we identified Ethyl (Z)-7-hexadecenoate as a male antiaphrodisiac. Supported by a grant of the FWF Austria (P09773-BIO).

Index terms: Osmia rufa, mating biology, chemical communication

Copyright: The copyrights of this original work belong to the authors (see right-most box in title table). This abstract appeared in Session 4 – CHEMISTRY AND PHYSIOLOGICAL ECOLOGY Symposium and Poster Session, ABSTRACT BOOK II – XXI-International Congress of Entomology, Brazil, August 20-26, 2000.