Trail pheromones are

semiochemical A semiochemical, from the Greek wiktionary:σημεῖον, σημεῖον (''semeion''), meaning "signal", is a chemical substance or mixture released by an organism that affects the behaviors of other individuals. Semiochemical communication c ...

s secreted from the body of an individual to affect the

behavior Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as we ...

of another individual receiving it. Trail pheromones often serve as a multi purpose chemical secretion that leads members of its own species towards a food source, while representing a territorial mark in the form of an allomone to organisms outside of their species. Specifically, trail pheromones are often incorporated with secretions of more than one exocrine gland to produce a higher degree of specificity. Considered one of the primary chemical signaling methods in which many social insects depend on, trail pheromone deposition can be considered one of the main facets to explain the success of social insect communication today. Many species of ants, including those in the genus ''

Crematogaster ''Crematogaster'' is an ecologically diverse genus of ants found worldwide, which are characterised by a distinctive heart-shaped gaster (abdomen), which gives them one of their common names, the Saint Valentine ant. Members of this genus are ...

'' use trail pheromones.

Background

In 1962, Harvard professor Edward O. Wilson published one of the first concrete studies constructing the groundwork for the notion of trail pheromones. Claiming an odor trail is deposited by the sting apparatus of the hymenopteran '' Solenopsis saevissima'' which results in a pathway from the colony to a food source, this study encouraged further investigation of how this chemical is laid, how it affects communication between species within and outside of its own, the evolution of the

, etc.

Mechanism

The pheromone is synthesized in the same region as venom, or other primary hormonal departments within the organism. Often, trail pheromone synthesis occurs in the ventral venom gland, poison gland, Dufour's gland, sternal gland, or hindgut. When secreted, the pheromone is dropped in a blotch-like fashion from the foraging organism onto the surface leading to the food source. As the organism proceeds to the food source, the trail pheromone creates a narrow and precise pathway between the food source and the nesting location, which another organism of the same species, and often the same nest, follows precisely. Commonly, an organism, when initially laying down the trail may renew the trail a number of times to demonstrate the value of the food source while running in tandem. Once the trail is laid, other members of the species will recognize the chemical signal and follow the trail, and each individually renew the trail on the way back to the home source. While this pheromone is constantly deposited by its members, the chemicals diffuse up into the environment propagating its message. Once the food source runs out the organisms will simply skip the task of renewing the trail on the way back, thus resulting in the diffusion and weakening of the pheromone. Studies have shown that with quality of food, distance from nest, and amounts of food, the strength of the trail pheromone may vary. Often the foraging individual may synthesize the trail pheromone as a mixture of chemicals produced by different glands which allows such specificity. While members of the same species who discovered the food constantly renew this trail pathway, as the chemical is secreted into the environment as a signal for food in their

umwelt In the semiotic theories of Jakob von Uexküll and Thomas A. Sebeok, ''umwelt'' (plural: umwelten; from the German '' Umwelt'' meaning "environment" or "surroundings") is the "biological foundations that lie at the very epicenter of the stu ...

, the very same chemical can often be interpreted as a territorial mark for outside species.

Insects that employ trail pheromones

Ants

Ants typically use trail pheromones to coordinate roles like nest defense and

foraging Foraging is searching for wild food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce. Foraging theory is a branch of behavioral ecology that studies the foraging behavi ...

. Ants can produce a trail of defensive secretions that trigger an alarm response within their nestmates. In regards to foraging, an ant can communicate the quality of a food source to its colony; the more rewarding a food source is, the higher the concentration of the trail produced. Additionally, some species, like ''

Lasius niger ) , official_languages = , languages_type = National languagesMyrmicine ants produce their trail pheromones through their poison glands. The major component in the trail pheromones secreted by '' Pristomyrex pungens'' is 6-''n''-pentyl-2-pyrone; several

monoterpene Monoterpenes are a class of terpenes that consist of two isoprene units and have the molecular formula C10H16. Monoterpenes may be linear (acyclic) or contain rings (monocyclic and bicyclic). Modified terpenes, such as those containing oxygen func ...

s were also found in the secretion, but they provided only marginal effects when combined with the former. The major components found in the secretions of '' Aphaenogaster rudis'' include anabaseine,

anabasine Anabasine is a pyridine and piperidine alkaloid found in the Tree Tobacco ('' Nicotiana glauca'') plant, a close relative of the common tobacco plant (''Nicotiana tabacum''). It is a structural isomer of, and chemically similar to, nicotine. Its ...

, and 2,3'-bipyridyl, though the third contributes less than the other two. When secreted, this trail pheromone does not recruit ants directly from their nest; instead, worker ants may stumble upon to the trail unintentionally and follow it thereafter to the food source

Bees

Bees can use trail pheromones to mark food sources and the entrance of their hives. Oftentimes, when finding a source, bees will mark that exact location as well as secreting pheromones along the flight back to their hives. Employment of trail pheromones is extensively studied in

honey bee A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the current cosm ...

s and

stingless bee Stingless bees, sometimes called stingless honey bees or simply meliponines, are a large group of bees (about 550 described species), comprising the tribe Meliponini (or subtribe Meliponina according to other authors). They belong in the family A ...

s, for both are highly social. The trail pheromone of the stingless bee ''

Trigona recursa ''Trigona'' is one of the largest genera of stingless bees, comprising about 32 species, exclusively occurring in the New World, and formerly including many more subgenera than the present assemblage; many of these former subgenera have been el ...

'' is produced by its labial glands. One of its key compounds is hexyl decanoate, and when secreted, the pheromone will recruit other bees towards the source. The stingless bee '' Scaptotrigona pectoralis,'' like ants, can utilize another colony's food trail. Specifically, they can learn foreign pheromone trails at a source, broadening their options for foraging. However, in some cases of aggressive bees, like ''

Trigona corvina ''Trigona corvina'' ( Cockerell, 1913) is a species of stingless bee that lives primarily in Central and South America. In Panama, they are sometimes known as zagañas. They live in protective nests high in the trees, but they can be extremely a ...

'', encounters between individuals from different colonies at a food source will result in fights and ultimately death amongst both parties.

Termites

Termites use trail pheromones primarily as a means of foraging. They can lay pheromones along a trail as their abdomens touch the ground, specifically through their abdominal sternal glands. As the other termites follow, they will continue to add to the trail. The basal termite ''

Mastotermes darwiniensis ''Mastotermes darwiniensis'', common names giant northern termite and Darwin termite, is a termite species found only in northern Australia. It is the most primitive extant termite species. Evolutionary significance This species shows uncanny s ...

'' produces trail pheromones from at least two sternal glands despite every other species producing theirs from only one. This pheromone, composed soley of a norsesquiterpene alcohol, elicits trail-following from other termites. As aforementioned, these successive termites can add to the trail, depending if it is used for foraging or recruiting workers to complete tasks. In the case of ''

Reticulitermes santonensis ''Reticulitermes'' is a termite genus in the family Rhinotermitidae. They are found in most temperate regions on Earth including much of Asia and the Middle East, Western Europe, and all of North America. Caste descriptions ''Reticuliterm ...

'', foraging trails have spotted markings throughout the path, whereas recruitment trails are more continuous from the termites dragging their bodies along the path.

Ecological significance

Trail pheromone deposition from an organism is correlated with its environment. In the event where a food source is identified and a trail pheromone is deposited, certain wildlife may flock towards or away from the trail causing temporary or '' dispersal'' of the population or individual. With relocation of wildlife, surrounding plant life may change as well; for example, pollen attached to the migrating organism is also relocating, thus may potentially regenerate in different patches.

Abiotic factors affecting trail pheromones

;Temperature :When the foraging organism's optimal foraging temperature is present, the organism will be more likely to search for food. Often, the further temperature falls out of this range, the less likely foraging will occur, thus, the less likely trail pheromones will be deposited. ;Season :Alongside with temperature, foraging occurs more during some seasons than others. With a change in season comes additional factors: a change in predators organism to avoid, change in food supply, and change in light availability. Often foraging organisms choose preference over such factors. ;Humidity :If it is too humid or not humid enough, organisms may choose not to forage. ;Other chemicals :Other surrounding chemicals may interfere with strength of pheromones.

Biotic factors affecting trail pheromones

;Surrounding animals :Although the pheromone may diffuse off as a territorial representation of the foraging organism, that does not secure the safety of the organism. In fact, this act may do the opposite and attract competing wildlife. With more surrounding predators, or competitors, comes more difficulty with foraging for a food source. Especially in cases were food is scarce, surrounding organism. Depending on the cost vs benefits tradeoff, an organism, in a situation where it may need the food supply, may be willing to risk the dangers to obtain it. Also, with more predators or competitors out there, the risks of foraging increase. ;Surrounding plants :Factors such as type and abundance of surrounding plants in an environment may certainly affect the degree of trail pheromone potency. Plants residing in close proximity to the odor trail may emit an abundance of chemicals which can either mask, change, or possibly even help propagate the signal. Additionally, areas saturated with plant life may block or alter trail pheromone diffusion.

References

{{reflist, 30em Pheromones Insect pheromones Semiochemicals Chemical ecology