Brian D. Jackson

Insect chemical communication: Pheromones and exocrine glands of ants

SummaryChemical communication plays a very important role in the lives of many social insects. Several different types of pheromones (species-specific chemical messengers) of ants have been described, particularly those involved in recruitment, recognition, territorial and alarm behaviours. Properties of pheromones include activity in minute quantities (thus requiring sensitive methods for chemical analysis) and specificity (which can have chemotaxonomic uses). Ants produce pheromones in various exocrine glands, such as the Dufour, poison, pygidial and mandibular glands. A wide range of substances have been identified from these glands.

3-Ethyl-2,5-dimethylpyrazine, a component of the trail pheromone of the antMessor bouvieri

3-Ethyl-2,5-dimethylpyrazine, found in the poison gland of workers, induces trail following in the Mediterranean harvester antMessor bouvieri. The poison gland contains on average 9 ng of this trail pheromone component. The alkaloids anabasine and anabaseine are also present in this gland, but induce no reaction in workers. Trail following is also induced by substances present in the Dufour gland, but the combined effect of both glands shows no synergism.

Trail pheromone of the antTetramorium impurum and model compounds: Structure-activity comparisons.

The major component of the trail pheromone ofT. impurum is methyl 2-hydroxy-6-methylbenzoate (methyl 6-methyl salicylate). The poison reservoir of each worker contains about 1.0 ng of this substance in the venom. To ascertain the degree of specificity of the substance as pheromone and to determine any correlation between structure and biological activity, 38 synthetic analogs were tested in a bioassay. Sixteen compounds showed activity at 100 ng per artificial trail. The importance of the methyl group and methyl ester were demonstrated, while the hydroxyl group has a relatively small effect.

Secretion of the Dufour gland of the antNothomyrmecia macrops (Hymenoptera:Formicidae)

The Dufour gland of the primitive Australian antNothomyrmecia macrops contains microgram quantities in total of linear alkanes and alkenes from C13 to C30 with heptadecene the major component (66%). In all, 50 substances, including methyl-branched hydrocarbons, aldehydes and acetates, α-farnesene and α-springene in low nanogram amounts, were identified by gas chromatography-mass spectrometry.

The dufour gland and the secretion placed on eggs of two species of social wasps,Liostenogaster flavolineata andParischnogaster jacobsoni (vespidae: Stenogastrinae)

The secretion placed on eggs and fed to larvae and the “ant guard” placed on the nest stalk ofParischnogaster jacobsoni contain the same hydrocarbons and in approximately the same proportions as is found in the Dufour gland. The secretion on eggs is a mixture of the contents of the Dufour gland and nectar. The emulsifying agent is a palmitic acid salt. Similarly, inLiostenogaster flavolineata, the egg secretion is an emulsion of nectar and Dufour gland secretion, which contains alkoxyethanol emulsifiers, found in nature for the first time.

The Dufour Gland Contents of Three Species of Euro-African Messor Ants and a Comparison with those of North American Pogonomyrmex (Hymenoptera: Formicidae)

Key Word Index--Messor minor; Messor capitatus; Messor bouvieri; workers; queens; Dufour gland; harvester ants; caste differences. Abstract--The Dufour gland secretions of Messor minor, Messor capitatus and Messor bouvieri differ from those of other myrmicine ants so far studied in having no sesquiterpenoids present. M. minor resembles the North American harvester ants, Pogonomyrmex, in containing branched chain hydrocarbons. Messor and Pogonomyrmex appear anomalous among myrmicines and more closely resemble some formicines in this respect. M. minor queens contain chiefly pentadecene (57%), a substance absent from workers (major substance, tridecane, 33%), but are otherwise similar. M. capitatus workers contain tridecane (28%) and nonadecane (26%) and no branched hydrocarbons. M. bouvieriworkers contain linear hydrocarbons, with heptadecadiene (50%) as the major substance, but also small quantities of citronellyl decanoate, a new natural product.

Secretion of the dufour glands of two african desert ants, Camponotus aegyptiacus and Cataglyphis savignyi (Hymenoptera: Formicidae)

Dufour glands of minor workers of Camponotus aegyptiacus contain a mixture of linear and methyl branched hydrocar- bons and a trace of dodecyl acetate. Major workers contain a similar mixture of hydrocarbons but also large quantities of dodecyl acetate, some other long chain acetates and traces of propionates and farnesyl acetate. Cataglyphis savignyi has pen- tadecane as the most abundant compound with traces of ketones, alcohols and an aldehyde. Camponotus vagus, a Mediterra- nean species, has a more b/pical formicine mixture with undecane being the major compound. A summary of Camponotus Dufour substances demonstrates the species-specificity of this secretion.

Contents of the pygidial gland of the ant Myrmecia nigriceps

The large pygidial glands of dolichoderine ants contain a variety of monoterpene compounds called iridoids [1], used as a defensive secretion. The contents have been extensively studied by Pavan, and later Cavill and their coworkers. Pygidial glands are found in all ant subfamilies except the Formicinae and seem to play a major part in chemical communication [2]. However, there are reports of identification of the chemicals in the gland of ants of only two other subfamilies. The ponerine ant Rhytidoponera metallica has been shown to contain 3-hydroxybenzaldehyde, isogeraniol, heptadecane, and heptadecene [2]. Another ponerine, Leptogenys diminuta, also contains isogeraniol as the principal component of the gland [3]. We recently reported [4] that the pygidial gland of the primitive ant Nothomyrmecia macrops (sole member of the subfamily Nothomyrmeciinae) contains 2,6-dimethylhept-5enal, 3,7-dimethyloct-6-en-2-one, indole, 3/-dodecalactone, and the hydrocarbons pentadecane, heptadecane, heptadecene, and heptadecadiene, all in low nanogram quantities. We now report an examination of the contents of the gland of Myrmecia nigriceps (Myrmeciinae), demonstrate the ability to give quantitative analysis of such tiny glandular tissues, and point to similarities between M. nigriceps and N. macrops. Workers of Myrmecia nigriceps Mayr were collected at Black Mountain, Australian Capital Territory, and Myrmecia pilosula (F. Smith) at Mongarlowe, New South Wales and at Hobart, Tasmania in February 1987. They were taken to Canberra, and there anaesthetized and killed by chilling to 5 0 °C. The pygidial glands, together with some cuticle, were dissected and sealed in soft glass capillaries (2 cm x 2 ram). Samples of non-glandular cu-

Chemical and behavioral studies on dufour gland contents ofManica rubida (Hymenoptera: Formicidae)

The Dufour gland ofManica rubida contains a simple mixture of (Z, E)-α-farnesene and (Z, E)-α-homofarnesene with tiny amounts of other faraesene, homofarnesene, and bishomofarnesene isomers. The gland also contains a mixture of very volatile compounds, chiefly acetone, with smaller amounts of acetaldehyde, ethanol, propanol, isobutyraldehyde, butenone, and butanone. The workers ofM. rubida are not attracted to these highly volatile compounds as are workers ofMyrmica species, butM. rubida workers show a strong increase of linear speed when stimulated by a freshly isolated gland. This response of increased speed of bothM. rubida andM. trubra to their own or each others Dufour gland secretion is consistent with the presence of the farnesenes in them both.

Dufour gland contents of three species ofMyrmecia (Hymenoptera: Formicidae), primitive ants of australia

Chemical investigation of the Dufour gland contents of three species ofMyrmecia by GC and GC-MS showed thatM. gulosa andM. nigriceps contain predominantly linear hydrocarbons, whereasM. pilosula contains acetates, aldehydes, and propionates. The major components ofM. gulosa andM. nigriceps are (Z)-8-heptadecene, pentadecane, and heptadecane. Their chemical profiles are similar to each other and to that ofNothomyrmecia macrops, the most primitive living ant, placed by itself in a separate subfamily. The major components ofM. pilosula are hexadecyl acetate, (Z)-9-octadecenyl acetate, (Z)-11-eicosenyl acetate, and (Z)-11-eicosenal. Some geographical variation was observed in the relative proportions of the components. The chemotaxonomic significance for the primitive Australian ant subfamilies Myrmeciinae and Nothomyrmeciinae is considered. The possibility is discussed that 11-eicosenal or geranylcitronellol, minor components of the Dufour gland secretion ofM. gulosa, may be responsible for the aggressive behavior released by the natural stinging secretions.