Cuticular hydrocarbons as sex pheromone of the bee Colletes cunicularius and the key to its mimicry by the sexually deceptive orchid, Ophrys exaltata

Male Colletes cunicularius bees pollinate the orchid, Ophrys exaltata, after being sexually deceived by the orchid's odor-mimicry of the female bee's sex pheromone. We detected biologically active volatiles of C. cunicularius by using gas chromatographic-electroantennographic detection (GC-EAD) with simultaneous flame ionization detection. After identification of the target compounds by coupled gas chromatography-mass spectrometry (GC-MS), we performed behavioral tests using synthetic blends of the active components. We detected 22 EAD active compounds in cuticular extracts of C. cunicularius females. Blends of straight chain, odd-numbered alkanes and (Z)-7-alkenes with 21-29 carbon atoms constituted the major biologically active compounds. Alkenes were the key compounds releasing mating behavior, especially those with (Z)-7 unsaturation. Comparison of patterns of bee volatiles with those of O. exaltata subsp. archipelagi revealed that all EAD-active compounds were also found in extracts of orchid labella. Previous studies of the mating behavior in C. cunicularius showed linalool to be an important attractant for patrolling males. We confirmed this with synthetic linalool but found that it rarely elicited copulatory behavior, in accordance with previous studies. A blend of active cuticular compounds with linalool elicited both attraction and copulation behavior in patrolling males. Thus, linalool appears to function as a long-range attractant, whereas cuticular hydrocarbons are necessary for inducing short-range mating behavior.