The nature and evolution of swarming in tropical social wasps (Vespidae, Polistinae, Polybiini)

Absconding (evacuating) swarms of social wasps following damage to nest or brood are more likely when the brood is young. Reproductive (fissioning) swarms in Metapolybia aztecoides occur during periods of much competition among queens. When a well-developed queen or group of queens is present nest enlargement rather than swarming may follow peaks of female production. In times of worker shortage neither nest enlargement nor swarming occurs. Seasonal swarming is reported in some species from 5 - 20 N. latitude, and from 12 - 35 S. latitude. Preparations for swarming include regrouping, cessation of nest building, unusual readiness to fly when disturbed, buzzing runs, trail marking, and, sometimes, brood cannibalism, aggressive begging, new nest initiation, and temporary aggregation along the swarm route. Old workers serve as scouts. Swarming individuals independently search for scent marks, with efficiency probably improved by use of prominent landmarks, conservation of direction and altitude between marks, and close spacing of marks at turns. Two possibly intergrading modes of trail following distinguish «diffuse» and «clumped» swarms. The trail pheromone is probably derived from sternal gland secretions originally important in dominance and territoriality, and subsequently used as «assembly» pheromones, orientation cues, recruitment signals, and (finally) markers guiding long migrations. There may be some co-evolution of pheromonal trail marking by swarming females and that of conspecific males. Honeybee swarming, like wasp swarming, is associated with periods of marked intracolony reproductive competition, whose onset is timed via regulation of queen rearing.