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The best mating strategy for males differs from that of females, because females gain from mating with several males (polyandry), but males gain from monopolizing the females. As a consequence, males have evolved a variety of methods, such as the transfer of inhibitory substances from their accessory glands, to ensure exclusive paternity of the female's offspring, generally with detrimental effects on female fitness. Inhibitory substances have been identified as peptides or other specific molecules. Unfortunately, in social insects male-mating traits are investigated only poorly, although male social insects might have the same fundamental influence on female-mating behavior as found in other species. A recently developed technique for the artificial insemination of bumblebee queens allowed us to investigate which chemical compound in the mating plug of male bumblebees, Bombus terrestris L., prevents females (queens) from further mating. Surprisingly, we found that the active substance is linoleic acid, a ubiquitous and rather unspecific fatty acid. Contrary to mating plugs in other insect species, the bumblebee mating plug is highly efficient and allows the males to determine queen-mating frequencies.linoleic acid ͉ multiple mating ͉ male-mating strategy ͉ female monopolization

IntroductionAnts are social insects, generally organized into large colonies where the numerous workers, infertile females, do most of the labours except procreation, which is reserved to the exiguous males and queens. All three castes use chemicals for communication, though as yet we know little about the substances specific to males and queens. The ants have inside their bodies a number of tiny glands in which they produce (or sequester) and store a curious variety of natural products. These distinctive and diminutive laboratories have been the subject of study of chemists and biologists in recent years. The substances studied generally have small molecules, sufficiently volatile to be studied by gas chromatography, and are presumed to have a pheromone function, though that has not been proven, or even tested in all cases. These glandular substances from ants are the subject of this review.The ants belong to the family Formicidae, which is divided into eleven subfamilies:' Ponerinae, a primitive group common in Australia; Myrmeciinae, the 'bull ants' of Australia; Dorylinae, the Old World army ants; Ecitoninae, the New World army ants; Leptanillinae, Pseudomyrmecinae, and Nothomyrmeciinae, three small groups; Myrmicinae, the largest group, to which our temperate red ants belong; Aneuretinae, a fossil group with only one known species today; Dolichoderinae, a chiefly tropical group; and Formicinae, those that produce formic acid, and to which our black wood ants belong.The exocrine glands (i.e. those secreting to the outside) of ants produce a range of substances for communication that fall under the general heading of 'semiochemicals' (chemicals which convey information between organisms). Pheromones are only one type of semiochemical and transmit information between members of the same species. Semiochemicals used for interspecific communication are called allelochemics. Three main types of allelochemics are recognized; allomones, kairomones, and synomones. An allomone is a chemical emitted from an insect, which gives adaptive advantage to the odour-releasing individual (e.g. defensive and repellent secretions). In contrast, a kairomone gives an advantage to the receiver of the odour (e.g. substances that enable the predator to locate its prey). The chemical trails of the army ant, Neivamyrmex nigrescens are picked up by predators like the blind snake Leptotyphlops dulcis and the beetle Hellumorphoides t e x a n ~s , ~ which feed mainly on the brood of the ants. A synomone

The chemical composition of the secretions of the metapleural glands of workers and soldiers of twoAtta species,Atta sexdens rubropilosa andA. cephalotes, and workers ofAcromyrmex octospinosus, has been studied. As indicated by infrared spectrometry and confirmed by the ninhydrin test, the secretions contain chiefly proteins. Of the volatile acidic portion, which is present as ionized salts, phenylacetic acid is the major component in workers and soldiers ofA. s. rubropilosa andA. cephalotes. BothAtta species also contain 3-hydroxydecanoic acid and its homolog as minor components together with indoleacetic acid. While there are qualitative similarities in the acidic composition in the secretions ofA. s. rubropilosa andA. cephalotes, they differ quantitatively. The secretion ofAcromyrmex octospinosus contains 3-hydroxydecanoic and indoleacetic acids, but lacks phenylacetic acid. The bactericidal and fungicidal actions of the three major substances have been confirmed.