Trigona spinipes

Like all other stingless bees, Trigona spinipes is highly social. When foraging, the workers utilize polarized odor-trail communication to relay the locations of food sources to each other. Unlike classic pheromone trails which extend from the food source to the nest, these polarized pheromone signals are short and do not reach the nest. They likely evolved to be short so as to not lead eavesdropping predators back to their nest.[7] What makes these trails polarized is that they are strongest at the food source and taper off moving away from it. This allows other bees following the signal to arrive at the food in large numbers without wasting time looking for food along the trail.[7] Octyl octanoate is the most significant component of the trail pheromone. It is emitted from the cephalic labial glands of Trigona spinipes and makes up approximately 74% of the secretion. Studies found synthetically produced octyl octanoate to be equally attractive to natural extract derived from the labial glands of foragers.[5]

Because Trigona spinipes queens only mate once in their lifetimes, there is tremendous competition between males to copulate with virgin queens. Usually 30–50 but sometimes even hundreds of males can be counted near virgin queen colonies in lek-like groups. The males come from great distances and from a variety of nests. There is a very low probability that a male will ever mate. They stay inside the colony until the age of 2–3 weeks and then leave the nest and live the life of a solitary male bee, which might be 4–6 weeks. While living alone, they will forage with conspecific workers and may follow these workers back to their nests to learn the locations of conspecific nests.[10]

While Trigona spinipes workers follow their nest-mates pheromone trails to food resources, they have been shown to follow scent marks left by another stingless bee Melipona rufiventris. They do this when they are foraging for new sources of food. Afterwards, Trigona spinipes will attack foraging Melipona rufiventris bees and take over their food. Some hypothesize that honey bee dance evolved to prevent eavesdropping espionage of this sort.[7]

The pheromone signal laid down by Trigona spinipes have been found, surprisingly, to be a deterrent to the more dominant stingless bee species Trigona hyalinata. The reason for this is not clear, but it is hypothesized that the dominant specie wants to avoid costs and injuries associated with seizing a food source from Trigona spinipes rather than finding its own source.[13] Trigona hyalinata are attracted to food sources with fewer Trigona spinipes foragers, because they can easily overpower a small number of their competitors.[14]

Trigona spinipes is locally known for its aggressiveness. Despite lacking the ability to sting, workers will pursue intruders and bite them. Each of their two mandibles have 5 sharp teeth. A study found that among 12 stingless bees investigated, Trigona spinipes was one of the 6 species that engaged in suicidal biting. The phenomenon of suicidal biting involved workers biting a target intruder so tenaciously that a significant number of the workers suffered fatal injuries. Of the 6 bees which engaged in suicidal biting, Trigona spinipes displayed the most aggressive behavior overall.[15]

Sex in Trigona spinipes is determined by whether or not the eggs are fertilized. Fertilized eggs are diploid and become females while unfertilized eggs are haploid and become males. Caste determination is trophic, meaning that it is not hereditary, but rather depends on the quantity and quality of food consumed by larvae.[16] Female larvae which consume better and higher quality food develop 12 rather than the usual 4 ovarioles at the pupal stage which later develop into queens. This trophic caste determination is the reason that Trigona spinipes queens are larger than workers. There is no size difference between queens and workers in other Meliponini species which utilize trophogenic caste determination mechanisms.[17] Virgin queens pose a threat to established queens. They are usually not needed by the colony so they are usually either killed by workers or imprisoned.[18]

Although they are smaller and have fewer ovarioles than queens, workers retain the ability to lay viable eggs. This ability is somewhat limited. Workers which are in close proximity to the queen often lay trophic or sterile eggs presumably due to hormone signals from the queen. In addition, the queen caste routinely consumes eggs laid by workers.[16]

Unlike what might be expected for such large colonies, there is no polyandry or polygyny in Trigona spinipes, such as can be found in honeybees. The sperm limitation hypothesis for the evolution of polyandry postulates that polyandry – the behavior of a queen mating with multiple males – evolved partly as a way for the queen to obtain enough sperm to fertilize her eggs. A positive correlation has been found between polyandry and colony size across a variety of insects including ants, bees, and wasps. Polyandry also has the advantage of promoting genetic diversity in large colonies, which promotes disease resistance, as has been shown in other bee species that are usually monandrous.[19] As such, since Trigona spinipes are not polyandrous, the mechanisms by which they promote genetic diversity are not clear.[12]

The fact that Trigona spinipes colonies are headed by singly mated queens leads to conflict between workers and the queen over male production. Workers have the ability to lay unfertilized haploid eggs which will develop into males. Kin selection argues that it is in the workers favor to do this. This is because each worker is more related to her own sons (relatedness=0.5) than to the queen's sons (relatedness=0.25). In bee species such as honeybees, which are headed by polyandrous queens workers, workers are more related to the queen's sons (relatedness=0.25) than they are to each other's sons (relatedness = 0.125), so they consume each other's sons in a phenomenon known as worker policing. However, this is not the case in Trigona spinipes. There is ongoing conflict between queens and workers over egg laying with eggs constantly being consumed. This conflict may explain why Trigona spinipes, unlike honeybees, lay male and female eggs in identical cells. This makes it more difficult for workers to determine where the queen's male eggs are located.[18]