Acromyrmex fracticornis is a species of leaf-cutter ant, a New World ant of the subfamily Myrmicinae of the genus Acromyrmex. This species is from one of the two genera of advanced attines (fungus-growing ants) within the tribe Attini. It is found in the wild naturally in southern Brazil, Paraguay and northern Argentina.

Overview

Commonly known as "leaf-cutter ants" they are a species of ant from one of the two genera of advanced attines within the tribe Attini.

Head view of ant Acromyrmex fracticornis specimen.

Acromyrmex can be identified from the closely related Atta genus of leafcutter ants since they have 4 pairs of spines and a rough exoskeleton on the upper surface of the thorax.

A mature Acromyrmex fracticornis colony contains mostly sterile female workers. They are divided into castes, based mostly on size, that perform different functions. Acromyrmex exhibit a high degree of biological polymorphism, four castes being present in established colonies – minims (or "garden ants"), minors, mediae and majors. Majors are also known as soldiers or dinergates. Each caste has a specific function within the colony. Acromyrmex ants are less polymorphic than the other genera of leafcutter ants Atta, meaning that there is comparatively less differential in size from the smallest to largest types of Acromymex. The high degree of polymorphism in this genus is also suggestive of its high degree of advancement.

Like Atta, Acromyrmex subsists mostly on a particular species of fungus (genus Leucocoprinus) which it cultivates on a medium of masticated leaf tissue. This is the sole food of the queen and other colony members that remain in the nest. The media workers also gain subsistence from plant sap they ingest whilst physically cutting out sections of leaf from a variety of plants.

Before leaving their parent colonies, winged females take a small section of fungus into their bucchal pouches and it is with this that the subsequently wingless queens 'seed' the fungus gardens of incipient colonies, cutting and collecting the first few sections of leaf themselves.

Acromyrmex has evolved to change foodplant constantly, preventing a colony from completely stripping off leaves and thereby killing trees, thus avoiding negative biological feedback on account of their sheer numbers. However, this does not diminish the huge quantities of foliage they harvest.

Acromyrmex fracticornis colony densities are positively correlated with basal grass coverage and the amount of grazing damage. A. fracticornis preferentially harvested tender grass blades that showed little or no previous damage by other invertebrates. They preferentially harvest Digitaria smutsii and Panicum maximum more often than other species, and Pennisetum purpureum, Pennisetum ciliare and Brachiaria decumbens were selected significantly less often.

Synonyms

• Acromyrmex jorgenseni Gonçalves, 1961
• Moellerius fracticornis Forel, 1909

See also

• List of leafcutter ants

References