Mycol. Res. 95 (11): 1308-1311 (1991) Printed in Great Britain

Leucoagaricus weberi sp. nov. from a live nest of leaf-cuttingants

J. J. MUCHOVEj', T. M. DELLA LUCIN AND R. M. C. MUCHOVEJJ

1308

1 Departamento de Fitopatologia, 2 Departamento de Biologia Animal, 3 Departamento de Biologia Geral, Universidade Federal de Virosa, 36.570Vii'osa, MG, Brazil

The basidiomycetes which are cultivated by ants are not well documented taxonomically owing to the lack of adequate specimens.Leucoagaricus weberi is described from a living nest of leaf cutting ants and compared with known species, and a new sectionOleoagaricus, is proposed to accommodate species of Leucoagaricus which possess oleiferous hyphae.

Leaf-cutting ants cultivate fungi on cut leaf and flower parts inan underground garden, and the fungus produces hyphae withinflated tips which are used as food by the ants (Wilson, 1971).These fungi are reported to belong to the Basidiomycotinaeven though clamp-connexions have not been found on thehyphae (Kreisel, 1972). Lack of positive identification of thefungi from nests is due to the absence of the fruiting structuresrequired for taxonomic diagnosis since the ants apparently donot permit the formation of basidiocarps (Wilson, 1971).Basidiocarps of ant nest fungi, of which there are only tworeported in the past century, are from an old abandoned nestor from pure culture (Weber, 1938, 1957; Wilson 1971).Rozites gongylophora Moller was collected from an abandonedgarden of Acromyrmex ant in Southern Brazil. The name of thisfungus was later transferred to Pholiota (Fr.) Kummer bySaccardo (1895), and is considered a species of Leucoagaricus(Singer, 1975), although formal transfer was not made. Theplacement of this fungus in Leucoagaricus is improbable sincethe fungus was described as having ochre-coloured spores(Saccardo, 1895) which is not consistent with Leucoagaricus.The other species was isolated as mycelium from a nest ofCyphomyrmex ants and the basidiocarps formed in pure culturein the absence of the ants. This fungus is considered to beLeucoagaricus wichanskyi (pilat) Singer (Singer, 1975). Mollerapparently did not consider his species to be the fungus ofAcromyrmex ants (Weber, 1957) even though this is mostprobable since the energy requirements necessary to producethe basidiocarp are such that the fungus must have been thepredominant one in the ant nest. The fungus of Alta specieshas not yet been reported.

Fig. 1. In vitro ant nest with basidiocarp being formed. Note thehoneycomb mass of fungus-cut leaves, and the mass of fungus-cutleaves that the ants have placed on top of the basidiocarp. p =

pileus; m = mass of fungus-cut leaves. h = honeycomb. The ants(workers) may be seen as small streaks (arrowheads). Bar = 1 em.

J. J. Muchovej, T. M. Della Lucia and R. M: c. Muchovej

Fig. 2. Leucoagaricus weberi. Lyophilized basidiocarp. dorsal and ventral views. Bar = 1 em.

1309

During sociological studies of Atta sexdens subsp. rubropilosa,reared in vitro (Della Lucia, Vilela & Moreira, 1987), abasidiocarp of an agaricoid fungus formed in a living garden.The ants were unable to suppress the expansion of thebasidiocarp, although they did cut parts from the pileus capin an attempt to inhibit its opening. They also piled cut leafand flower parts on top of the basidiocarp in an attempt toreincorporate it back into the garden (Fig. 1). The basidiocarpwas removed and placed in a sterile jar containing moistcotton to maintain humidity. The basidiocarp increased about10 % in size in 2 d and began to open by splitting the partialveil. The veil was incompletely ruptured but still formed anannulus which was held to the stipe by filaments of hyphae.

Based on the following characteristics, the fungus belongsto the genus Leucoagaricus (Locq.) Singer and is described asnew.

Leucoagaricus weberi Muchovej, Della Lucia & R. Muchovej,sp. nov. (Figs 2-5)

Etym: for N. A. Weber, American entomologist who didmuch of the initial work with fungi from ant nests

Basidiomata hemiangiocarpica, lepiotoidea, alba. Pileus umbonatus,albus, squamulosus reeurvatus, atro-brunneus vel niger; annulusmembranaceus, ad stipes hyphis adhaerens. Stipes cylinder-centralisad basim incrassatus. Lamellae Iiberae, albae. Basidia cum 4 sporae,26-31 x 9-12 ~m. 5porae hyalinae, dextrinoideae, obclavatae, laeves,8'5-10 x 4-5 ~m.

Holotypus: Herbario UFV, 10 Apr. 1990, J. J. Muchovej.

Basidiocarps hemiangiocarpic, lepiotoid, with a cylindricalstipe, white in colour. Pileus convex to slightly umbonate,recurved squamulate, the squamules of parallel hyphae, whichon the ends are dark brown to black, revealing white contexthyphae beneath, margin crisped, context of parallel hyphae,clamp-connexions not seen, staining dark reddish brown inlactophenol, 8 mm thick at the apex to membranous at themargin, not staining with ammonia, oleiferous hyphae present,not exuding. Stipe cylindrical, bulbous at the base, 20 mmdiam" 10 cm high, initially white but drying brown to reddishbrown; annulate, annulus membranous to fleshy, only slightlyadherent to the stipe by hyphal stands, initially present as anannular veil; volva absent. Lamellae free, crowded, white andwrinkled; lamellar trama intermixed to weakly parallel, clamp­connexions not seen. Cystidia absent. Basidia 4-spored,26-31 x 9-12 j..\m. Spores hyaline, dextrinoid, metachromatic,broadly obclavate, smooth, uni- to biguttulate in ammonium,germ pore small in the thickened wall, eccentric, apparent asa minute thinness of the wall, spores 8'5-10 x 4-5 ~m.

Oleiferous hyphae produce an oily to resinous substance inthe basidiocarp tissue and are visible as large thickenedhyphae. The oily to resinous long-chain hydrocarbons shouldproduce high energy content which the ants harvest from thefungus, Fungal parts which the ants consume are said to havea high carbohydrate content (Quinlan & Cherrett, 1979).

The section of Leucoagaricus to which this fungus belongs isunclear. Characters which exclude it from the other sections(Singer, 1975) are spores less than 12 ~m (from Macrospori

Leucoagaricus weberi from a live nest of leaf-cutting ants

3

1310

Figs 3-5. Microstructure of Leucoagaricus weberi. Fig. 3, Basidium and spores. Fig. 4, basidium with underlying tissue. Fig. 5, hymenialtrama with oleiferous hyphae (oh).

Singer); smooth spores (from Sculpturati Singer); lamellae notchanging with ammonia (from Piloselli (Kuhn.) Singer); a well­developed annulus and epicutis of fibrils (from Sphaero­cystophori Singer). The other 2 sections, Rubrotincti andLeucoagaricus, have similar characteristics of spore size andbeing moderate to fleshy, and overlap in characteristics ofspore print, germ spore and presence of fibrils. The differencebetween these two sections is due to the darkening of thecontext. The production of oleiferous hyphae in any of thesesections has not been reported, and since these hyphae arequite evident and are a distinct morphological character, theintroduction of a new sectional name to accommodate thespecies is warranted.

Section Oleoagaricus Muchovej, Della Lucia & R. Muchovej,section nov.

Sporae minus quam 12 I-lm, laeves, hyalinae, porus germen imper­fectus ad inconspicuus. Contextum constans, cum hyphae oleiferosae.Pileus squamulosus, atro-brunneus vel niger.

Typus Leucoagaricus weberi Muchovej, Della Lucia & R. Muchovej

Spores less than 12 I-lm, hyaline, smooth, with an incompleteor inconspicuous germ pore. Context unchanging, witholeiferous hyphae. Pileus with brown to black squamules.Moderate fleshy species.

This is the first time any agaricoid fungus has been foundin an active ant nest in which the ants were still cultivating the

garden. The ants apparently secrete antibiotic substanceswhich suppress the growth of other fungi and bacteria(Weber, 1956). If the health of the fungal garden declines,other fungi quickly overgrow the garden and suppress thegrowth of the ant's fungus (Muchovej & Della Lucia, 1990;Weber, 1966). Therefore, this indicates that the basidiocarpwas from the species which the ants cultivate since aninvading fungus would not be able to obtain sufficient energyto reproduce from the ant nest without eliminating thecolony.

Leucoagaricus weberi differs from the species previouslydescribed in that P. gongylophora produces ochre-colouredspores and the cap scales are purple-brown (Saccardo, 1985)and L. wichanskyi which has smaller spores and does not havesquamules or oleiferous hyphae (Weber, 1957).

This research was supported in part by the ConselhoNacional de Desenvolvimento Cientifico e Technol6gico(CNPq), Brazil.

REFERENCES

Della Lucia, T. M., Vilela, E. & Moreira, D. D. O. (1987). Criando sauvas emlaborafrios. Gincia Hoje 6, 25-29.

Holldobler, B. & Wilson, E. O. (1990). The Anls. Cambridge, MA: BelknapPress.

Kreisel. J. (1972). Pilze aus Pilzgarten von Alia insulares in Kuba. Zeilschrifl fUrAllgemeine Mikrobiologie 12, 643--654.

J. J. Muchovej, T. M. Della Lucia and R. M. C. Muchovej

Muchovej, J. J. & Della Lucia, T. M. C. (1990). Escovopsis a new genus fromleaf cutting ant nests to replace Phialocladus nomen invalidum. Mycotaxon37, 191-195.

QUinlan, R. j. & Cherrett, j. M. (1979). The role of fungus in the diet of theleaf-cutting ant Alta aphalotes (L.). Ecological Entomology 4, 15 1-160.

Saccardo, P. A. (1895). Sy/loge fungorum II, 152.Singer, R. (1975). The Agaricales in Modern Taxonomy. Vaduz: j. Cramer.Weber, N. A. (1938). The biology of the fungus-growing ants. Part III. The

(Received for publication 19 March 1991 and in revised form 10 April 1991)

1311

sporophore of the fungus grown by Alia Ctphalotes and a review of reportedsporophores. Revista de Entomologia 8, 264.

Weber, N. A. (1956). Treatment of substrate by fungus-growing ants.Anatomical Record 125, 504.

Weber, N. A. (1957). Fungus-growing ants and their fungi Cyphomyrmexcostatus. Ecology 38, 480--494.

Weber, N. A. (1966). Fungus-growing ants. Science 153, 587---<i04.Wilson, E. O. (1971). The Insect Societies. Cambridge, MA: Belknap Press.