Mating expenditures reduced via female sex pheromone modulation in the primitively eusocial halictine bee, Lasioglossum (Evylaeus) malachurum (Hymenoptera : Halictidae)

The present paper reports on behavioral experiments and gas chromatographic analysis of chemical communication in the mating biology of the primitivel y eusocial sweat bee Lasioglossum (Evylaeus) malachurium. In a dual-choice experiment, a female made odorless was significantly less attractive than a n untreated one. Attraction in L. (Evylaeus) malachurum is therefore mediat ed by a female-produced sex pheromone. Further bioassays showed that unmate d gynes are more attractive to males than mated ones. Males are able to dif ferentiate between the two groups of females as little as 3 h after mating. Biotests with different samples obtained from attractive gynes showed surf ace extracts to be most attractive. Behavioral tests with synthetic copies of the compounds identified as cuticular constituents of virgin gynes were highly attractive to males; the volatile bouquets consisting of n-alkanes, n-alkenes and isopentenyl esters of unsaturated fatty acids were the most a ttractive samples. Isopentenyl esters of unsaturated fatty acids were the k ey compounds in inducing male inspections as well as stimulating pounces an d copulatory attempts. Virgin and nesting gynes differed clearly in the rel ative and absolute amounts of the volatiles on the cuticle. The total amoun t of volatiles was significantly higher in virgin gynes and decreased in br eeding queens. Hydrocarbons were the dominant group of compounds in both gr oups of females. The relative amounts of the wax-type ester, hexadecyl olea te, isopentenyl eaters, and a hitherto unidentified steroid were higher in attractive virgin gynes, while the relative proportions of hydrocarbons and lactones dominated in nesting queens. The site of sex pheromone production in attractive young L. (Evylaeus) malachurum gynes remains unknown. Head g lands or Dufour's gland secretions may be involved. Another possible source of the 'active principle' found among the cuticular lipids could be glandu lar cells of the epidermis. The significance of modulation of female sex ph eromone composition is discussed in terms of a reduction in mating expendit ures.