Social wasps, such as European hornets (Vespa crabro) and Southern Yellowjackets (Vespula squamosa), are fascinating social insects that live in organized and hierarchical colonies. Their life cycle is complex and includes a larval stage essential to the proper functioning of the colony.
Larval Development: A Synchronized Life Cycle
The development of social wasp larvae is a precise and synchronized process that begins with the laying of eggs by the queen. The queen lays oval-shaped, whitish eggs in hexagonal cells built in the nest. She can lay several hundred eggs per day, ensuring the colony's survival. After a few days of incubation, the eggs hatch and give birth to tiny, whitish, legless larvae that are entirely dependent on adults.
Larval Growth
Social wasp larvae go through several larval stages before metamorphosing into adults. Each larval stage is characterized by an exponential increase in the size and weight of the larva. Workers feed the larvae with captured and chewed prey. The larvae's diet consists primarily of caterpillars, insects, and other invertebrates, the exact composition varying depending on the wasp species. The larvae communicate with the workers through chemical signals, allowing them to request food.
- For example, larvae of Vespula squamosa produce a chemical substance called "food begging pheromone," which attracts workers to their cell.
- A study conducted in 2018 showed that the production of this pheromone is regulated by the amount of food consumed by the larva.
Larval development is influenced by several environmental factors, including temperature and humidity. Optimal temperatures and constant humidity promote rapid growth and healthy development.
Metamorphosis
Once larval growth is complete, the larvae undergo a spectacular metamorphosis. The larva transforms into a pupa, a phase of rest and transformation. The pupa is immobile and wrapped in a silk cocoon. During this phase, the larva undergoes a profound physiological and morphological transformation, developing the wings, legs, and other characteristic structures of the adult.
The development time from larva to adult varies depending on the species and environmental conditions. For Southern Yellowjackets (Vespula squamosa), for example, the complete life cycle lasts approximately 40 days.
Larval Behavior: More Than Just a Mouth to Feed
Social wasp larvae are not simply food receptacles. They play a crucial role in the proper functioning of the colony.
The Primordial Role of Larvae in the Colony
- Larvae produce pheromones, chemical substances that influence the behavior of adults. These pheromones enable communication within the colony and contribute to social cohesion.
- Larvae contribute to the development of the colony by consuming a large amount of food, thus promoting the growth and development of adults and the queen.
The size of the colony is directly related to the number and development of the larvae. Larger colonies have a larger number of larvae, which feed a larger number of workers, allowing the colony to thrive and develop. A study on European hornets (Vespa crabro) showed that colonies with a larger number of larvae have a better ability to capture prey and defend their territory.
Larval Behavior
Social wasp larvae exhibit unique and well-defined behaviors. The larvae adopt specific postures to communicate their nutritional needs and other information to the workers. For example, a larva that needs food will twist and move around in its cell.
Larvae also interact with each other. They can sometimes compete for food resources, but they can also cooperate to regulate the temperature of the nest. Studies have shown that Southern Yellowjacket larvae can coordinate their movements to create air currents that help ventilate the nest and maintain an optimal temperature.
Adult Behavior Towards Larvae
Adults in the colony exhibit specific parental behaviors towards the larvae. Workers constantly feed, protect, and clean the larvae. The larvae have a direct influence on the behavior of adults. For example, the presence of larvae stimulates the production of pheromones that regulate the reproductive behavior of adults. The queen will lay more eggs when the colony has a large number of larvae, ensuring the colony's continued growth.
Although the larvae are generally well cared for, cases of cannibalism may occur in some colonies. Workers may eliminate weak or sick larvae to ensure the survival of the colony. This behavior is particularly common during times of food shortage or when the colony is threatened.
The Relationship Between Larvae and Adults: A Complex and Essential Symbiosis
The relationship between larvae and adults is a complex symbiosis essential for the survival of the colony. Larvae are a source of food for adults. Workers can regurgitate food for the larvae, but the larvae also produce nutrient-rich salivary secretions that adults consume. This process, called trophallaxis, allows for resource sharing and strengthens social bonds within the colony.
Larvae produce pheromones that contribute to the social cohesion of the colony and regulate the behavior of adults. The pheromones emitted by the larvae can influence the reproductive behavior of the queen, the production of workers, and even the defense activities of the colony. The larvae also play a crucial role in the reproduction of the queen. Pheromones produced by the larvae stimulate the queen to lay more eggs.
The transmission of genetic information from the queen to the larvae is essential for the sustainability of the colony. Genetic variations among larvae can influence their development and behavior, contributing to the evolution of social wasp colonies.
The development and behavior of social wasp larvae are fascinating aspects of the biology of these social insects. Understanding these processes allows us to better understand social life and complex interactions within wasp colonies.