Social Insect Communication: More Than Just Sexual Signals

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    Imagine… you are a worker honeybee searching for nectar and pollen from a flower, suddenly you see a fellow worker bee wagging its body and walking in a circular pattern. Using the directions from the dance and the release of pheromones you now know where a flower full of nectar is! Because of this communication between the worker insects, the location of food is shared. Social insects are found mostly in the orders Hymenoptera and Isoptera. Social colonies are made up of castes in which the insects play different roles, mainly egg layers, and workers. 

Solitary vs. Social Insect Communication

Both solitary and social insects communicate, however, strictly solitary insects communicate only to attract and transfer signals with mates. Social insects have much more complicated communication. These sexual signals are often chemical but can also be visual, acoustic, vibrational, or tactile. Higher levels of sociality lead to communication of division of labor, resource utilization, nestmate recognition, and collaborative defensive actions. However, it is not necessarily true that social insects have increased brain capacity. It has been documented that the part of the brain involved in processing long-term memory and signals is smaller in social paper wasps than in solitary potter wasps (both wasps are in the same family). This could be because social insects thrive off each other, demanding limited cognitive ability. However, social reproductive females of the Halictine bee were found to have larger mushroom bodies than workers or solitary Halictine bees. 


Queen Signals

Queen signals indicate the queen's presence or fertility to workers who can help raise the young. Worker insects can also use this information to control others' reproduction by destroying eggs laid by other workers. When a colony loses its queen, the queen signal is lost, and nonsterile workers can start laying eggs. Queens of red fire ants (Solenopsis invicta), produce pheromones that inhibit reproductive activity in virgin queens and reinforce the helping behavior of the workers. The European honeybee (Apis mellifera), has a complex queen mandibular pheromone (QMP) that regulates worker ovarian activity, inhibiting the raising of new queens, attracts workers and males, coordinates swarming, and delays the transition from nursing to foraging. Looking at the evolutionary history of queen pheromones, social male drones prefer chemical profiles of unmated over mated females, like solitary insects. These queen pheromones may have evolved from the compounds that are produced at the onset of ovarian activity in solitary insects. 


Nestmate Recognition

To protect an insect colony, only nestmates can be allowed to enter the nest. This is important for preventing non-members from exploiting a nest’s resources. Recognition chemical cues are used. When two individuals meet, they touch each other with their antennae and sense the others' recognition cues. If the cues are unfamiliar then the individual will respond aggressively. Colonies adjust how often they incorrectly reject nestmates and incorrectly accept non-nestmates. For example, when nectar is scarce, honeybee guards lower the acceptance threshold, even if they may accidentally reject nestmates. 


Recruitment

Recruitment is the process of directing foraging workers to a resource, usually food. Directing others to the food source and motivating others to forage can be done using the same or different signals. Honeybees do this using the waggle dance, pheromones, and flower odors motivating nestmates to forage and communicate the location of the food. Stingless bees will mark the food patch or leave a scent trail. Bumblebees use excited runs and the release of recruitment pheromones to inform others about food resources. In ants and termites, small colonies have recruiters that guide others to the food source, large colonies use trail pheromones to guide a group of others to the source. 


Alarm signals

Insects have alarm signals to communicate distress, most of which are chemical. For example, isopentyl acetate is released when something is stung, triggering more honey bees to sting. Honeybees only react to IPA when they are in groups and are most sensitive to it when they are close to the entrance of the colony. Alarm pheromones cause two different responses depending on the size of the colony. When the alarm is released, small colonies disperse, and large colonies attack and defend. When threats are urgent, acoustic alarm signals are beneficial because they travel fast. Some ants drum their substrate, causing faster and more aggressive responses to a future-emitted alarm pheromone.


 Sources

Wenseleers, T., & van Zweden, J. S. (2017). Sensory and cognitive adaptations to social living in insect societies. Proceedings of the National Academy of Sciences of the United States of America, 114(25), 6424–6426. https://doi.org/10.1073/pnas.1707141114 


Leonhardt, S., & Menzel, F., Nehring, V., Schmitt, T. (2016). Ecology and Evolution of Communication in Social Insects, Volume 164, Issue 6, Pages 1277-1287, ISSN 0092-8674, https://doi.org/10.1016/j.cell.2016.01.035.

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