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Dearth and Colony Impact

Posted August 7, 2025

A nectar dearth or simply dearth is a natural seasonal gap when few or no plants are blooming with nectar-rich flowers. It typically occurs:

In July and August in Ohio
After the spring and early summer nectar flows (e.g., clover, black locust)
Before the fall flow (e.g., goldenrod and asters in September)

Many beekeepers recommend feeding your bees during the nectar dearth. It’s often stated as a requirement but why is that? As a backyard beekeeper do I have to feed? Let’s learn a little more about this time of the year and its impact on the honey bee so you have more information to help answer that question for yourself.

Longevity

Beginning at the end of summer nectar flow (dearth) and early fall, worker bees with increased longevity (up to four times that of spring months) gradually appear in the colonies. By mid-fall, long-lived workers constitute the majority of the hive population. In addition to the greater longevity, these bees are different from their sisters that were produced in spring in their hypopharyngeal gland size, juvenile hormone and vitellogenin levels, and hemolymph protein content. The appearance of these long-lived bees is linked with times when the colonies’ natural brood production is reduced or stopped (e.g. brood breaks), which can happen during dearth, winter months or queen loss, creating a need for these bees to sustain the colony population into the next season. Studies have shown that increased longevity even in a tropical-adapted honey bee can occur under typical tropical seasonal changes that result in the reduction of foraging.

Worker bees in temperate regions normally live for up to 60 days in the foraging season while a subpopulation of workers produced at the end of summer survive routinely more than 200 days through the winter. It’s also been found that average worker longevity was significantly higher in the dearth season (reduced brood) compared to when resources are ample (increased brood). This can even be scientifically demonstrated in the spring and summer months by eliminating open brood, younger larvae that are fed by nurse bees and in cells that are not sealed with silk and wax, which results in emerging worker bees that become “winterized” and live up to 5 months.

This may explain the feeling that beekeepers have about queenless colonies that seem to last forever. From the information above what is happening is that the last sections of emerging workers are winterized because there isn’t brood pheromone to trigger their development. This allows them to live slightly longer, have the time for a worker to develop and eventually lay unfertilized eggs (drones). These drones become the colonies’ last attempt in spreading their genes during a future mating flight. This trait also allows a small portion of a colony that is swarming to live slightly longer, providing time for the queen to emerge, mature, get matted and return to begin laying. The colony may have to wait on average ~48 days before new workers will emerge to begin their maturing process requiring even more days before taking over as foragers to feed the colony.

Pre-Foraging Age

Lifespan is a fundamental life-history trait that can exhibit tremendous variation between individuals of a given population. Variation in lifespan is generally linked to both intrinsic and extrinsic pressures acting separately or interacting with each other. While intrinsic mortality risk is due to ageing (physical and functional degradation of the body), extrinsic mortality risk rather refers to environmental hazards (e.g. pollution, parasites, climate and predation).

Honeybees are social insects that exhibit striking caste-specific differences in longevity. While honeybee queens can live up to 5 years, workers usually only live 2 to 6 weeks in the summer and about 20 weeks in the winter. The 10-fold difference between the summer and winter worker bee lifespan relies on differences in both intrinsic physiological senescence (aging) processes and extrinsic factors like exposure to environmental pressures (i.e. winter bees rarely leave the safe environment of the hive). In fact, as a result of age polyethism (work activities), the extrinsic mortality risk of summer bees is not constant throughout the individual’s life. Bees spend the first weeks of their adult life performing tasks within the hive environment but then switch to foraging activity that exposes them to environmental hazards such as temperature, predation or dehydration. In addition, the transition to foraging activity is accompanied by a reduction in protein and lipid reserves, as well as the glycolipo protein vitellogenin, a major antioxidant. Foragers will then experience constant probability of death over time, but they may also face the depletion of limited glycogen reserves essential to their flight activity. The age at the onset of foraging (AOF), which can be modulated according to the size, demography and needs of the colony, as well as by several environmental factors, is, therefore, assumed to be an important driver of the lifespan of worker bees.

Test results show that the age at the first flight and onset of foraging are critical factors that determine, to a large extent, lifespan. Most importantly, the results indicate that a large proportion (40%) of bees die during pre-foraging stage, and for those surviving, the elapsed time and flight experience between the first flight and the onset of foraging is of paramount importance to maximize the number of days spent foraging. Once in the foraging stage, individuals experience a constant mortality risk of 9% and 36% per hour of foraging and per foraging day, respectively. These risks can also vary based on environmental situations and increasing resource demands during times such as dearth. In conclusion, the pre-foraging stage during which bees perform orientation flights is a critical driver of bee lifespan.

Seasonal Worker Mortality Rates

We find that there are seasonal differences in honeybee colony variability to both intrinsic and extrinsic worker mortality. Colonies are most flexible to extrinsic (age-independent) nurse and forager mortality during periods of higher extrinsic mortality and resource availability but most elastic to intrinsic (age-dependent) mortality during periods of lower extrinsic mortality and lower resource availability such as during dearth or winter.

We find that there are seasonal differences in the strength of selection against senescence (decline in physiological functioning and lifespan) in honeybee workers, as measured by the sensitivity of the colony growth rate to age-dependent worker mortality. We find that the colony is more sensitive to changes in both nurse and forager senescence in winter conditions, when resources are scarce and extrinsic mortality is lower, than in summer conditions, when resources are plentiful and extrinsic mortality is high. The colony’s sensitivity to forager senescence is even higher when winter also reduces brood survival. Since colonies cannot easily produce new workers in winter, small increases in the senescence of existing workers have larger effects on the colony. This difference in sensitivity may largely explain why winter honeybee workers have a much lower senescence rate than spring or summer workers. In contrast, colonies are most sensitive to changes in extrinsic mortality in summer when resources are plentiful; this may be because summer workers spend more of their lives in the riskier forager state rather than the more protected nurse state.

Environmental Cues and Lifespan

Honey bee colonies respond rapidly to environmental conditions. The proximal cue of artificial rainfall causes a shift to conservation physiology in a matter of hours. Similarly, forage dearth or persistent low temperatures can shift physiology towards colony thermoregulation or resource conservation including production of the diutinus (long-lived) worker phenotype, defined by worker longevity and conservation physiology. Diutinus workers consume and digest pollen in the fall, or at the beginning of a pollen dearth, then conserve the nutrition internally to provide for the growing colony when environmental conditions improve. With the coming of winter, pollen diversity and nutrition disappear completely across the northern landscape and decrease drastically on the southern landscape. While the diutinus phenotype is well documented in northern climates, there is little to no data on its expression during mild winter conditions typical of the southern US including Texas, Florida and California where an economically significant number of commercial bee colonies overwinter annually since these mild conditions allow for continued foraging opportunities. These mild winters involve a variety of indistinct or conflicting environmental cues, including warm daily temperatures, and the availability of pollen and nectar in the landscape. Subsequently, brood rearing over winter commonly discontinues in predictably cold (Northern) climates, but continues at significantly reduced levels in southern climates, stimulating foraging behavior throughout the winter and eliminating the possibility of diutinus workers because the presence of brood in the hive environment accelerates both behavioral and cellular senescence (aging) among worker bees. After approximately 10 days of foraging, workers experience a sharp increase in mortality (shortening of their lifespan). It could be stated then that southern states do not have winter or long-lived bees and to keep these colonies of short-lived bees from dying must provide resources by moving them to foraging opportunities and/or constant feeding.

Colony Size

Honey bees balance colony populations against available food resources by adjusting brood rearing during nutritionally stressed periods such as dearth, winter or cold wet springs. Workers limit colony populations primarily through brood cannibalism of eggs and young larvae but often resume brood rearing when conditions improve. However, extended brood cannibalism possibly during a lengthy dearth or winter period reduces brood and removes brood signals that mediate brood rearing, such as E-β-ocimene, a vola-tile pheromone produced by eggs, young larvae, prepupae and ovipositing queens.

Robbing

In a social species like the honey bee, changes in foraging strategy require shifts in several groups of specialized workers that are involved in collecting, storing, and processing food. In cases of extreme food shortage, honey bee colonies can switch to a high-risk, high-reward foraging tactic known as honey robbing, which involves stealing mature honey from other colonies. Colonies engaged in honey robbing show a corresponding increase in defensive behaviors displayed by specialist guard bees, presumably because the conditions that provoke robbing also increase the risk of colony invasion. Previous studies suggest aggressive behaviors displayed by robbing forager nestmates modulate guard defensiveness. We found little evidence that food type influences forager interactions with guards. Rather, conflict at the feeder (hive or open feeder) is the best predictor of increased aggressive interactions, even when accounting for the effects of seasonal change. Thus, intraspecific conflict at the food resource during robbing may drive shifts in individual forager aggression, activating guard defensiveness as one component of a syndrome of colony-level changes required to accommodate the robbing foraging tactic.

For example, while foraging activity and aggression are known to increase simultaneously during honey robbing, the specific cues driving this behavior remain unclear. Furthermore, although studies have shown that the levels of serotonin and dopamine, which are related to aggressive behavior, peak in the bee brain during August and September (dearth), the possible relationship between these biochemical changes and the frequency of honey robbing remains unknown.

Referenced Materials

Ask Why: The Hobbyist Beekeeper

Health and Immunity

Extracting Layens Honey Frames

STOP PRETENDING.

START BEE-TENDING.

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