Honey Bee Communication: Pheromones

Introduction

Queen, Worker and Drone honey bee image. Together with the honey bee dance, honey bee pheromones represent one of the most advanced ways of communication among social insects.

The composite organization of the honey bee society, which consists of three adult castes (queen, worker, and male) and non-self-sufficient brood, provides for many coordinated activities and developmental processes and thus needs a similar elaborate way of communication among the colony members. Pheromones are the key factor in generating and maintaining this complexity, assuring a broad plasticity of functions that allow the colony to deal with unforeseen events or changing environmental conditions.

The honey bee society cannot function without effective communication. Most honey bee communication occurs by smell and taste. The intricate system of chemical messengers are termed hormones and pheromones. Pheromones are chemical substances secreted by an animal’s exocrine glands that elicit a behavioral or physiological response by another animal of the same species. In honey bees the targets of pheromonal messages are usually members of the same colony, but there are some exceptions in which the target can be a member of another colony

Pheromones are involved in almost every aspect of the honey bee colony life: development and reproduction (including queen mating and swarming), foraging, defense, orientation, and in general the whole integration of colony activities, from foundation to decline. Pheromones allow communication among all the honey bee castes: queen–workers, workers–workers, queen–drones, and between adult bees and brood.

Pheromones

In honey bees, as in other animals, there are two types of pheromones: primer pheromones and releaser pheromones. Primer pheromones act at a physiological level, triggering complex and long-term responses in the receiver and generating both developmental and behavioral changes. Releaser pheromones have a weaker effect, generating a simple and transitory response that influences the receiver only at the behavioral level.

In the following paragraphs the main honey bee pheromones are described, based on the honey bee caste to which they belong and the glands responsible for their production. In the first part of the chapter the effect (or the effects) exerted by each pheromone on the receivers and on the bee colony will be illustrated, while the neurophysiologic and molecular mechanisms of the response to the chemicals will be discussed later.

Queen Pheromones

Impact of Releaseer and Primer Pheromones by honey bee queen.\

Releaser and primer effects of the queen signal, which regulates colony functions and development. Stimulating effects are indicated as “+” and inhibiting effects as “–.”

The honey bee queen represents the main regulating factor of the colony functions. This regulation is largely achieved by means of pheromones, which are produced by different glands and emitted as a complex chemical blend, known as the “queen signal.”

The queen signal acts principally as a primer pheromone, inducing several physiological and behavioral modifications in the worker bees of the colony that result in maintenance of colony homeostasis through establishment of social hierarchy and preservation of the queen’s reproductive supremacy. More specifically, the effects of the queen signal are maintenance of worker cohesion, suppression of queen rearing, inhibition of worker reproduction, and stimulation of worker activities: cleaning, building, guarding, foraging, and brood feeding. It is known that when the queen is old or sick (low pheromonal signal) or it dies (no pheromonal signal), workers are driven to rear new queens from young brood within 12–24 hours; the removal of the queen in absence of young brood soon leads to the decline of the colony: the workers stop performing their activities and start to lay unfertilized eggs that develop into male adults (drones); the colony becomes disorganized, unfit, dirty, susceptible to diseases and prey of predators; it rapidly depopulates and goes toward a certain death.

In addition to its primer effect, the queen signal exerts an attractive releaser effect: it calls workers around the queen in a retinue group, which is stimulated to feed and groom her; in young premating queens it acts as attractant for drones during the mating flights; during swarming it keeps the swarm together.

When the queen is stationary on the comb she is surrounded by a circle of workers known as “court” or “retinue” that face toward her and feed, palpate, and lick her. Usually the retinue is composed of eight or 10 workers. QMP secretion, which represents the main constituent of the queen signal and its components are accountable for the formation of the retinue. The attention paid by retinue workers increases when the virgin queen becomes mated and lays eggs, and then decreases as she grows old. The degree of attractiveness of the queen is null at 0–1 day old, medium from 2 to 4 days old, and high from 5 days to 18 months old. Mating is a crucial factor for the development of the chemical signal of the queen and its attractive effect on workers. QMP also suppresses both queen supersedure and swarming by its dispersal throughout the colony

Alarm Communication

Alarm pheromones are widely distributed in social insects. Honey bees have two different alarm pheromones, one from each end of the body. The mandibular glands of workers produce 2-heptanone and one of the glands of the sting produces isopentyl acetate. The sting pheromone is better known and is the major alarm chemical.

The chemical released when a bee stings, isopentyl acetate, is absent in newly emerged workers whereas bees 15+ days of age have one to five mg. There are several other components of the gland such as acetates and alcohols and they may work in conjunction with isopentyl acetate. Actual stinging or defensive behavior is correlated with isopentyl acetate. Defensive behaviors range from alerting to flying (buzzing); if disturbance persists stinging is the last response. Bees display a faster reaction time and more concentrated defensiveness upon perception of the alarm pheromone. Generally, bees will respond to alarm pheromone only at or near the colony, not in the field. Smoke in some way masks the pheromone.

The second alarm pheromone, 2-heptanone, is produced in worker mandibular glands. It, like isopentyl acetate, is absent in newly emerged workers but is present by foraging age. Bees respond to 2-heptanone at the nest entrance similarly as they do to isopentyl acetate, but it is not nearly as effective in producing a response, requiring 20 to 70 times as much compound before bees respond. Queen and drones lack 2-heptanone.

Scent or Nasonov Gland

Graphic showing honey bee using navonov gland Workers have a scent (Nasonov) gland at the tip of the abdomen. The gland emits a mixture of seven terpenoids which serve primarily in orientation. To release the chemical mixture the workers stand high on the hind legs with the abdomen elevated and tilt the last abdominal segment downward while fanning the wings. Bees use the scent to help sisters locate home, food, and water sources. It acts with queen substance in a pheromone concert to keep the bees of the swarm together.

Other Pheromones

Honey bees have a trail pheromone that includes chemicals released from their lowest leg segment, which serve as orientation pheromones. Brood, drones, and beeswax comb emit pheromones . the former helps to maintain queen dominance as it is responsible for retarding worker reproductive organ development. The mixture of pheromones plus the distinctive queen signature pheromone, mix with food odors to give each bee colony a distinctive hive odor. Hive odor is not a specific pheromone but does impart a chemical identity to each social unit.