0. Abstract

The weakening of a honey bee colony rarely results from a single isolated factor. Most often, it is a gradual process in which multiple constraints—parasitic pressure, nutritional imbalance, thermal disturbances, or exposure to toxins—interact and progressively reduce the resilience of the superorganism.

The model presented in this article describes three main spirals that can self-reinforce: an infectious spiral, a chilling spiral, and a starvation spiral. As long as the population remains sufficient and healthy, the colony can compensate for these disturbances. When resilience declines, regulatory mechanisms become fragile and the weakening dynamics accelerate.

Understanding this logic allows the beekeeper to recognize early warning signs sooner and to intervene before multiple spirals become established simultaneously. The goal is not to eliminate all risk, but to maintain a sufficient level of population and health to preserve the colony’s adaptive capacity.

1. A colony in balance: a living and resilient system

A honey bee colony is not a simple aggregation of individuals, but a superorganism capable of fine regulation and continuous adaptation (Tautz, 2008). Under normal conditions, it naturally hosts viruses, bacteria, fungi, and parasites without collapsing. The presence of pathogens therefore does not automatically mean disease.

The stability of the colony relies on several complementary mechanisms: flexible demographic organization, collective thermoregulation, and immunity that is both individual and social. Some weakened workers spontaneously leave the hive—a behavior sometimes described as “altruistic suicide”—thereby helping to limit the spread of infectious agents (Rueppell et al., 2010).

The longevity and physiological robustness of bees are strongly linked to vitellogenin, a key protein produced in the fat body that plays a role in regulating ageing, immune function, and division of labor (Amdam et al., 2005). Likewise, ethyl oleate, a pheromone produced by foragers, modulates the transition of young bees to foraging and contributes to internal demographic balance and age polyethism (Leoncini et al., 2004).

As long as these mechanisms function harmoniously, the colony can absorb temporary disturbances: climatic variation, moderate parasitic pressure, or fluctuations in floral resources. Collapse is generally not abrupt; it results from a progressive imbalance when several stress factors act simultaneously and exceed the system’s regulatory capacity.

2. Triggering factors: when balance becomes fragile

In the field, weakening situations most often result from a gradual combination of constraints. In most cases, several constraints add up and progressively fragilize the colony. Four categories of stress recur regularly in the literature and in beekeeping practice: lack of food, parasites and viruses, cold or thermal disturbances, and exposure to toxins (vanEngelsdorp et al., 2009).

The parasite Varroa destructor plays a central role in this dynamic. Beyond its direct effect on bees, it acts as a vector and amplifier of viruses, notably Deformed Wing Virus (DWV), thereby increasing the infectious load within the colony (Rosenkranz et al., 2010). Poorly controlled parasitic pressure is now one of the most well-documented factors in colony losses.

The nutritional factor is just as decisive. Insufficient availability of pollen or nectar leads to metabolic stress, reduced body reserves, and a shortened lifespan of workers (Naug, 2009). An underfed colony becomes more vulnerable to infections and less able to ensure brood thermoregulation.

Climatic conditions also play a role. Prolonged periods of cold or large thermal fluctuations can disrupt brood development. Suboptimal temperature during the pupal phase influences behavioral performance and the robustness of adult bees (Tautz et al., 2003; Jones et al., 2005).

Finally, repeated exposure to pesticides or certain acaricide treatments can act as an additional stressor, weakening bee physiology and increasing sensitivity to pathogens (Medrzycki et al., 2010).

Taken in isolation, each of these factors can sometimes be compensated by the colony’s adaptive capacity. It is when several of them interact simultaneously that the risk of imbalance increases sharply.

3. The logic of spirals: when stress self-amplifies

 

A weakened colony generally does not collapse overnight. The process is often gradual and silent. The conceptual model presented here is inspired by the work of Oliver (2010), enriched and complemented by subsequent scientific data from apidological research. A first disturbance—whether parasitic, nutritional, or climatic—leads to a slight decrease in population or worker performance. As long as this loss remains moderate, collective regulatory mechanisms can compensate.

However, some disturbances have a particular feature: they not only weaken the colony, they also change its ability to defend itself. When a reduction in bee numbers decreases thermoregulation, food provisioning, or immune efficiency, the system enters a self-amplifying dynamic. One initial loss leads to a second, which triggers a third.

This type of dynamic is referred to as positive feedback: the effect reinforces the initial cause. In honey bee colonies, several spirals can establish themselves simultaneously and evolve in parallel. An infection promotes worker loss; worker loss disrupts thermoregulation; impaired thermoregulation further weakens bees. The dynamic becomes circular.

It is important to emphasize that these spirals do not systematically lead to collapse. A strong colony can interrupt the process if conditions improve or if the beekeeper intervenes in time. But when several loops become established simultaneously, resilience decreases rapidly.

In the following sections, three main spirals are described: the infectious spiral, the chilling spiral, and the starvation spiral. They do not necessarily occur in sequence; they can coexist, mutually reinforce one another, and evolve at different speeds.

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Spiral 1 – The infectious spiral: when viral pressure exceeds regulation

Deformed Wing Virus

Viruses are part of the normal environment of honey bee colonies. Many colonies harbor viruses at low levels without showing apparent symptoms. The situation changes when the viral load increases rapidly or when the bees’ immune capacity decreases. The parasite Varroa destructor plays a decisive role here. By feeding on larvae and adult bees, it directly weakens individuals and acts as a vector for viruses, notably Deformed Wing Virus (DWV). The simultaneous presence of the parasite and a high viral load leads to amplification of infection within the colony (Rosenkranz et al., 2010).

Bees have antiviral mechanisms, notably RNA interference (RNAi), which helps limit viral replication by neutralizing certain messenger RNAs (Maori et al., 2009). As long as these mechanisms function effectively, infection can remain controlled.

The spiral begins when several factors weaken this regulation: nutritional stress, exposure to toxins, or high parasitic pressure. Increased mortality reduces the number of workers available for brood care and food provisioning. A weakened colony then produces fewer robust bees, which further facilitates viral spread.

The beekeeper may observe only a developmental stall, irregular brood, or a gradual decline in the adult population. By the time losses become clearly visible, the spiral is often already well established.

However, it should be recalled that a strong colony can interrupt this negative dynamic if parasitic pressure decreases or if overall conditions improve. The infectious spiral is not irreversible; it becomes problematic when it combines with other stressors.

Spiral 2 – The chilling spiral: when thermoregulation becomes insufficient

Maintaining a stable brood temperature is one of the essential collective functions of a colony. Bees actively regulate the temperature around 34–35 °C through coordinated behaviors: heat production via isometric muscle contraction, clustering, ventilation, and strategic distribution of workers (Tautz, 2008). When the population decreases, thermoregulatory capacity weakens. An insufficient number of adult bees makes it more difficult to maintain a stable brood temperature. In cold or unstable periods, this can lead to repeated thermal fluctuations and disrupted larval development.

Conversely, during strong heat, a very weakened colony may also lack enough bees to ensure effective ventilation and cooling. Excessive brood temperatures then increase physiological stress and can impair the quality of emerging bees. In temperate regions, this risk mainly concerns weak colonies during summer.

Studies have shown that suboptimal temperatures during the pupal phase influence adult behavioral performance, notably learning and orientation capacities (Tautz et al., 2003; Jones et al., 2005). Other work suggests that disrupted development may also increase sensitivity to certain pesticides (Medrzycki et al., 2010).

The chilling spiral becomes established when worker loss reduces thermoregulation, producing adult bees that are less performant or more fragile. These bees contribute less effectively to resource collection and brood care, leading to a further decrease in the active population.

This process can remain subtle. The beekeeper may observe brood thinning due to chilling (not to be confused with patchy brood due to disease), slowed development, or a colony that struggles to cover all brood-box frames. As long as the population remains sufficient, the colony can stabilize. But if this spiral combines with infectious pressure or lack of food, the imbalance accelerates.

Spiral 3 – The starvation spiral: when the food flow breaks down

A colony does not depend only on its honey reserves. Its balance relies on a continuous flow of nectar and, above all, fresh pollen, which is indispensable for brood rearing and for maintaining the physiological functions of workers. When the forager population declines, this flow quickly diminishes.

The loss of foragers can be linked to parasitic and/or infectious pressure, unfavorable weather, or exposure to toxins. Whatever the initial cause, the consequence is similar: fewer food inputs enter the hive. The colony must then draw on its reserves and reduce brood rearing.

An insufficient protein intake directly affects the bees’ fat body, a central organ for metabolism and immunity. Vitellogenin production decreases, influencing longevity, physiological robustness, and internal demographic balance (Amdam et al., 2005). Weakened bees live shorter lives and contribute less effectively to collective tasks.

The spiral sets in when reduced food inputs decrease worker quality and lifespan, which further reduces the number of active foragers. The colony progressively becomes unable to compensate for its losses. Metabolic stress also promotes increased susceptibility to infections, which can restart the infectious spiral described above.

In the field, this dynamic often translates into stalled development, a lack of bee bread, reduced wax production, or a colony that seems “light” despite the presence of brood. As long as outside inputs resume quickly or the beekeeper intervenes, the colony can rebalance. However, if this spiral combines with parasitic pressure or failing thermoregulation, the weakening process accelerates.

7. Interaction of spirals: when resilience erodes

Illustration: S. Imboden, 2026

The three spirals described above do not operate in isolation. In practice, they often evolve in parallel and can mutually reinforce one another. An infection weakens workers; weakened workers regulate temperature less effectively; disrupted thermoregulation produces less robust bees; a reduced population collects less food. The system becomes circular.

The central notion is not a single factor, but resilience. As long as the colony has a sufficient number of healthy bees, it can compensate for temporary losses. It adjusts division of labor, slows brood rearing, or mobilizes reserves. This plasticity is its main strength.

The situation becomes critical when the decline in bee numbers reaches a level at which essential collective functions can no longer be ensured properly. Thermoregulation, food provisioning, and infection control become simultaneously fragile. At that stage, each additional loss further reduces compensatory capacity.

This is not necessarily a precisely measurable threshold, but rather a functional tipping point. The colony can no longer absorb disturbances. The spirals self-amplify and the dynamics accelerate.

This phase can remain subtle for some time. The beekeeper may simply observe a colony that is “lagging behind,” less dynamic than others. Yet this is precisely when vigilance is decisive. Early intervention can still restore balance. When the population becomes too weak and only young, poorly nourished bees remain, recovery capacity decreases sharply.

Understanding this interaction of spirals makes it possible to change perspective: the objective is not only to treat an isolated factor, but to maintain at all times a sufficient level of population and health to preserve the resilience of the superorganism.

8. Early observation: recognizing weak signals

In many situations, colony collapse is not sudden. It is preceded by subtle signs that only attentive observation can detect. The colony does not “collapse” in a day; it slows down, stagnates, or seems less dynamic than the other hives in the apiary.

A first signal may be insufficient spring build-up: a brood area that does not increase despite favorable conditions, or a colony that does not cover the number of frames expected for the season. Irregular or thinned brood can reflect a demographic imbalance or infectious pressure.

The absence or low presence of bee bread is another important indicator. A colony raising brood without visible pollen stores is operating under strain. Similarly, reduced wax production or lack of activity during a nectar flow suggests that resource inflow is insufficient.

The behavior of bees at the hive entrance can also provide valuable information: unusual agitation, disorganized activity, or conversely low traffic despite good weather conditions.

These signals do not necessarily mean that a spiral is already out of control. They do indicate, however, that resilience may be decreasing. Regular, comparative observation of colonies within the same apiary remains one of the beekeeper’s most powerful tools.

Intervening early often makes it possible to interrupt an unfavorable dynamic before multiple spirals become established simultaneously. The earlier the action, the higher the chances of restoring balance.

9. Practical recommendations: acting before the spirals become established

In the field, preventing spirals from becoming established is based on a simple principle: maintaining a sufficient and healthy population. The aim is not only to correct a one-off problem, but to prevent multiple stressors from adding up and reducing the colony’s regulatory capacity.

1. Maintain low parasitic pressure

Regular control of Varroa destructor remains a priority. High parasitic pressure favors viral amplification and can trigger the infectious spiral. Regular monitoring of infestation, application of recommended treatments at the correct dose and appropriate time, and post-treatment evaluation help limit this risk (Rosenkranz et al., 2010).

2. Ensure continuous nutritional input

A well-fed colony resists infections and climatic variation better. The presence of sufficient honey and pollen reserves should be checked regularly, especially during critical periods (late winter, unstable spring, late summer). Supplemental feeding can be considered when natural resources are insufficient, in order to avoid prolonged metabolic stress.

3. Support thermoregulation

Hive space management should be adapted to colony strength. A weak colony should not be maintained in a volume that is too large to heat or ventilate. Conversely, in hot periods, adequate ventilation and an appropriate location reduce the risk of thermal stress.

4. Reduce exposure to toxins

Limiting exposure to agricultural pesticides and avoiding repeated or inappropriate use of certain acaricide treatments help preserve the physiological robustness of bees (Medrzycki et al., 2010). Prudent treatment management is an integral part of maintaining resilience.

5. Observe and compare colonies regularly

Comparing colonies within the same apiary makes it possible to detect early stagnation or developmental delays. A colony that remains consistently behind deserves special attention, even in the absence of striking symptoms.

6. Preserve a sufficient and healthy population

Maintaining an adequate number of healthy workers is the best safeguard against spirals becoming established. This requires coherent management of brood, reserves, and parasitic pressure throughout the season.

7. Do not combine collapsing colonies with healthy colonies

A colony in an advanced weakening phase may carry a high viral or parasitic load, even without spectacular symptoms. Combining it with a healthy colony can promote transmission of infectious agents and reactivate an infectious spiral. When in doubt, it is preferable to isolate or eliminate the weakened colony rather than risk contaminating the apiary.

10. Conclusion

A colony generally does not collapse because of a single isolated factor. Weakening often results from a progressive interaction between infection, thermal imbalance, and nutritional stress. Understanding this dynamic makes it possible to act earlier and more effectively.

The beekeeper’s objective is not to eliminate all risk, but to maintain a sufficient level of resilience so that the colony can absorb the inevitable disturbances of its environment.

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See also :

• Principles of honey bee feeding
• Recognizing healthy colonies
• Recognizing honey bee diseases
• Guide to honey bee health
• Vitellogenin
• Varroa does not feed on blood

 

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