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Acromyrmex is a genus of New World of the subfamily Myrmicinae. This genus is found in South America and parts of Central America, México and the Caribbean Islands, and contains 33 known species. Commonly known as "leafcutter ants" they comprise one of the two genera of advanced attines within the tribe Attini, along with Atta.
The antennae are the most important sense organs Acromyrmex species possess, and are jointed so the ant can extend them forward to investigate an object. It can retract them back over its head when in a dangerous situation, for example, a fight. Acromyrmex species have eyes, but their eyesight is very poor. Like all insects, the eye is compound eye, meaning it is made up of many eyelets called ommatidia, with the number of these eyelets varying according to species. Male ants tend to have more ommatidia than other castes. The ocelli, which are generally found on top of the heads of queens, are thought to aid aerial navigation by sunlight.
Acromyrmex is dark red in colour. In addition to the standard ant anatomy, the back of the thorax has a series of spines which help it manoeuvre material such as leaf fragments on its back.
Acromyrmex can be distinguished from the closely related leafcutter ant genus Atta by having four pairs of spines and a rough exoskeleton on the upper surface of the thorax compared to three pairs of spines and a smooth exoskeleton in Atta.
Much of the inside of the Acromyrmex head is occupied by the muscles that close the ; the muscles that open the jaws are much smaller. The brain, though tiny, is a very complex organ, and allows Acromyrmex to learn and react to its surroundings. It can remember colony odour, navigation, and where it has placed a certain object.
The heart is a long, tubular organ running the entire length of the body, from the brain to the tip of the abdomen. It has Heart valve within it that prevent blood from flowing the wrong way. The fluids bathing the internal organs is circulated by the heart; these fluids then filter through the organs and tissues. The pharynx, which is part of the gut, controlled by six muscles, pumps food into the oesophagus. Debris in the food, such as soil, is filtered before it enters the oesophagus and is collected in a tiny trap, the infrabuccal pocket. When this pocket becomes full, the Acromyrmex ant empties it into an area within or outside the nest designated as a waste-products area.
Several glands in the head secrete various substances, such as those responsible for the digestion of food. Another gland within the head produces digestive and, in some species, alarm chemicals; these chemicals are used to alert nearby ants of impending danger, and any ant that detects this alarm will automatically go into "battle mode". If an ant is crushed, a huge blast of this chemical is released, causing the entire colony to go into "battle mode".
The thorax contains muscles to operate the legs and wings and the nerve cells to co-ordinate their movements; also contained in this part of the body is the heart and oesophagus.
The abdomen contains the , poison glands, ovaries in the queen, and the Dufour's gland, among other things. Acromyrmex ants have two "stomachs", including a dry, social stomach in which they can store food and later regurgitate to larvae, the queen and other ants. This is separated from the stomach proper by a small valve; once food enters the second stomach, it becomes contaminated with gastric juices and cannot be regurgitated. The exact function of the Dufour's gland is unknown, but is thought to be involved in the release of the chemicals used in the production of odour trails, which the ants use to recruit nest mates to a food source. It may also produce sex-attractant chemicals.
Once on the ground, the female loses her wings and searches for a suitable underground lair in which to found her colony. The success rate of these young queens is very low and only 2.5% will go on to establish a long-lived colony. Before leaving their parent colonies, winged females take a small section of fungus into their infrabuccal pouches to 'seed' the fungus gardens of incipient colonies, cutting and collecting the first few sections of leaf themselves.
This mutualistic relationship is further augmented by another Symbiosis partner, a bacterium that grows on the ants and secretes chemicals; essentially, the ants use portable . Leafcutter ants are sensitive enough to adapt to the fungus' reaction to different plant material, apparently detecting chemical signals from it. If a particular type of leaf is toxic to the fungus, the colony will no longer collect it. The only two other groups of insects that have evolved fungus-based agriculture are ambrosia beetles and termites. The fungus cultivated by the adults is used to feed the ant larvae and the adult ants feed on the leaf sap. The fungus needs the ants to stay alive, and the larvae need the fungus to stay alive.
In addition to feeding the fungal garden with foraged food, mainly consisting of leaves, it is protected from Escovopsis by the antibiotic secretions of Actinomycetota (genus Pseudonocardia). This mutualistic microorganism lives in the metapleural glands of the ants.. Actinomycetota are responsible for producing the majority of the world's antibiotics today.
In Central America, leafcutter ants are referred to as "wee wee" ants, though not based on their size. They are one of the largest ants in Central America.
Deterring the leafcutter ant Acromyrmex lobicornis from defoliating crops has been found to be simpler than first expected. Collecting the refuse from the nest and placing it over seedlings or around crops resulted in a deterrent effect over a period of 30 days..
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