DeGrandi‐Hoffman and Chen 2015). Specifically, the binding of highly conserved structural motifs of pathogens by special receptors activate hemocyte‐mediated cellular events such as phagocytosis or encapsulation of the pathogen, induction of hemolymph coagulation or melanization, or the synthesis of antimicrobial peptides (DeGrandi‐Hoffman and Chen 2015). Further, RNA interference, a major antiviral immune response of insects, has also been identified in several honey bee studies (DeGrandi‐Hoffman and Chen 2015).
Age Polyethism
An age‐related division of labor among worker honey bees is well known, where younger bees perform the inside tasks (first two to three weeks of life), while older bees complete the outside jobs (last one to three weeks of life) (Winston 1987). However, because bees are sensitive to social changes within their colony, this division of labor is not firm and behavioral maturation of work activities may change, directly regulated by worker to worker interactions (Leoncini et al. 2004). For example, when a colony begins to lack older foraging bees, some bees commence foraging as young as five days of age, two weeks earlier than usual. Similarly, when a colony has an overabundance of older bees, younger bees delay their maturation to foraging (Leoncini et al. 2004).
The transition of a honey bee during aging from a life without flying and only inside hive tasks to one of outside defense and foraging, imparts unique functional demands and energy requirements (Elekonich and Roberts 2005). Vitellogenin, a storage protein produced in the fat body of insects and secreted into the hemolymph, plays a central role in such social organization of the honey bee colony, influencing social behavior, stress resilience, immunity, and longevity (Amdam et al. 2012). Besides guiding behavior and lifespan, vitellogenin also affects brood food production and worker specialization for pollen versus nectar collection (Nelson et al. 2007). Similarly, juvenile hormone acts to regulate the rate of behavioral development in honey bees, and guides many of the necessary conversions from a bee fostering brood to one collecting and processing nectar (Sullivan et al. 2000; Elekonich and Roberts 2005). Vitellogenin together with juvenile hormone are inversely correlated to the onset of foraging behavior in worker honey bees; younger nurse bees have low levels of juvenile hormone that increase with age and high vitellogenin, while older foraging bees exhibit the opposite relationship (Johnson 2010; Corona et al. 2007; Sullivan et al. 2000; Robinson 1987).
Other mechanisms are also involved in the behavioral transition of worker honey bees, including the queen and brood pheromones, which inhibit and accelerate worker maturation toward foraging, respectively (Doke et al. 2015; Bortolotti and Costa 2014). In addition, older foraging bees release a pheromone, ethyl oleate, that affects the behavioral maturation of young bees as outlined above, slowing down the transition of nurse bees into foragers (Leoncini et al. 2004). Complex models of division of labor in insect societies are proposed that integrate social, environmental, and nutritional factors, as well as both primer and releasing pheromonal mechanisms; the queen and brood pheromones, as well as vitellogenin and juvenile hormone are considered important parts of the story (Doke et al. 2015; Johnson 2010).
Overwintering Biology
Honey bees exhibit remarkable seasonal changes in their behavior and physiology in temperate climates with the changing seasons, as well as other tropical or arid climates following the cycle of flowering plants (Doke et al. 2015; Winston 1987). Winter conditions or a dearth in nectar and pollen production result in cessation of brood rearing and foraging, lifespans of the worker bee increase, and the active lifestyles of the worker and queen bees slow. Honey bees in temperate climates have stronger responses to seasonal changes compared to tropical areas (Winston 1987). Spring, summer, and fall worker bees (exhibiting an age‐based division of labor) complete most of the hive tasks – except for reproduction – sequentially with only a short lifespan of around 30–45 days, while winter honey bees – also known as diutinus bees – become generalists working to maintain a thermoregulating cluster and may live up to eight months (Winston 1987; Doke et al. 2015; Johnson 2010). Levels of vitellogenin help shape such seasonal changes in honey bee behavior and physiology and have a positive impact on lifespan; the short‐lived foraging worker bees produce less vitellogenin than nurse bees, wintering bees have the highest levels among workers, and the longest living queen bee has the highest levels of all castes (Amdam et al. 2012; Corona et al. 2007). Juvenile hormone levels (low in nurse and wintering bees) decrease in the fall and rise markedly in again in spring, suggesting that fall bees are already in their winter physiologic state, and overwintering bees return to a forager bee physiology in the spring (Doke et al. 2015; Fluri et al. 1982).
Temperature Regulation
Honey bees are heterothermic, meaning their individual temperature varies with the outside environment, yet they can also regulate body temperature via endothermic activity (Stabentheiner et al. 2010; Vidal‐Naquet 2015). In addition, honey bee larvae and pupae have a low metabolic rate and cannot maintain thermal constancy in a changing environment; therefore, the brood are strongly dependent upon nest temperature regulation for development (Stabentheiner et al. 2010; Kronenberg and Heller 1982). Fortunately, the social organization of the honey bee hive facilitates colony level homeostasis including the migration activity of the worker bees within the nest and various bee behaviors. Other factors including the size and insulating properties of the nest also affect colony thermoregulation. During the winter, when cooling of the colony occurs, a portion of the worker bees (those older than two days) produce heat by movement of thoracic flight muscles while other nest mates (less than two days old) remain ectothermic (Stabentheiner et al. 2010). Such heat conduction among bees provides effective heat transfer and helps maintain the brood nest temperature in a precise range of 32–36 °C for normal development. Similarly, various strategies are used by social honey bees to cool the nest when the temperature becomes too high, and temperatures above 36 °C are reported to damage brood and negatively affect development (Vidal‐Naquet 2015; Kronenberg and Heller 1982). Cooling of the nest cavity in warm conditions may occur via several mechanisms including dispersal of bees away from the brood, hive ventilation by worker bees fanning their wings or evaporative cooling using water at the hive entrance or within the colony (Winston 1987).
Part 2: Communication in Honey Bees
Renowned biologists, Hölldobler and Wilson (2009) stated, “the essence of social existence is reciprocal, cooperative communication.” Similarly, Seeley (1995) emphasized “all biologists are keenly aware of the amazing adaptive responses of cells and organisms, and are awed by the complexity of the underlying mechanisms of cellular and organismal physiology. But probably few biologists recognize that evolution has likewise endowed certain animal societies with impressive abilities and has fashioned elaborate mechanisms of communication and control inside these societies to produce their remarkable group‐level skills.” Thus, advanced communication processes have evolved in honey bee colonies to coordinate interactions among its members and enable their intricate social organization. For example, honey bees have developed a complex system of communication strategies (including various dance behaviors, chemical messaging, vision and olfaction, and magnetic fields) to help them locate and store food, grow, build and maintain their colony, locate and defend their hive, attract other bees and for many other colony activities (Seeley 1995; Winston 1987).
Physical Communication
Waggle Dance
Of the diverse methods of communication known to humankind, the honey bee dance language is among the most intricate and well‐studied in all of the animal kingdom (Hölldobler and Wilson 2009). The waggle dance of the honey bee is perhaps best known and permits foraging worker bees to precisely communicate the location and value of a food source. Through several ingenious experiments, the Austrian scientist Karl von Frisch first described this remarkable dance language where cooperative honey bees of a colony share food gathering information (von Frisch 1967). Once a honey bee locates a rich food source, say a patch of
