The influences of various kinds of stress on a honey bee colony are often ignored. Stress doesn’t cause a particular disease, but weakens a colony so that disease can get a foothold. A honey bee colony should be looked at as a “black box,” into which energy (pollen, nectar, water) flows and is then converted into products (honey, beeswax, brood, bees). Anything reducing energy flow into the box is termed stress. The beekeeper is interested in removing as much energy from the system (honey, wax or pollination in the form of worker bee energy) as possible. Paradoxically, therefore, the beekeeper becomes a component of stress on a colony.
Weather is perhaps the greatest potential source of colony stress. Inclement conditions slow down or stop altogether flow of nectar and pollen into a colony. In spring and early summer, the brood is consuming large amounts of energy (food). A sudden shut down of foraging (rainy conditions, confinement by the beekeeper for moving), if prolonged, causes severe stress. The bees’ solution is to stop brood rearing, reducing energy investment and colony growth. Good management provides food during this stress period. Providing a reliable water supply is also critical.
In cold weather, moisture must be ventilated or it can cause stress on the cluster, which is attempting to keep the brood warm. Temperature fluctuation also causes stress. The brood nest temperature needs to be maintained (93 to 95 degrees F.) for normal brood development. Anything interfering with temperature control (colonies located in cold locations or in damp conditions) causes more energy (more bee work fueled by pollen and nectar) to be funneled into heat production. Chilled brood is an excellent example of stress on a colony. Too much brood for the available adult population to cover results in individuals on the outside of the brood nest to die. More energy is required to produce replacement individuals and energy is also required to remove the dead larvae or pupae.
Again, any phenomenon interfering with internal efficiency is termed stress. Some of the more important factors are: number of adult bees, ratio of adult bees to brood, and egg laying rate of the queen. All these go into determination of the energy necessary to operate the colony. Because older larvae are provisionally fed (a little at a time as needed), there must be a population of young bees in proportion to larvae requiring feeding. The queen’s egg laying rate is regulated to allow for this constantly changing ratio by the colony. Other adults must also be available to provide nectar and pollen required by the nurses (which usually don’t forage) to feed the larvae. Conditions that can radically change a population balance are swarming,Swarming pesticide poisoning and beekeeper caused conditions including moving colonies, making splits or shaking a package.
The best general rule to avoid stress is maintaining a strong (large population) colony of bees. Strong hives are capable of dealing better with environmental fluctuation. They can also more quickly change bee ratios for efficient colony operation. All this is not to make an already complex subject less understandable. Rather it is to plead for more concise observation and clearer thinking when developing conclusions and/or contemplating solutions to declines in colony productivity. The successful beekeeper is one who knows when to let the bees alone, yet actively helps them through stressful times to attain their maximum productivity (energy output).
Stress is also implicated in outbreaks of other brood diseases and viruses. Incidences of chalkbrood and sacbrood have also been correlated with this phenomenon.
Viruses are responsible for a number of diseases of either brood or adults. The best known viral brood disease is sacbrood Fortunately, it is relatively rare. Many adult viruses have been detected, but they occur only sporadically and except for reducing stress on colonies, there are no preventative recommendations. This has completely changed since the introduction of the Varroa bee mite, however, causing a lot of headaches in the beekeeping community.
Control of an adult disease affecting all honey bees is one of the few success stories in disease management. Nosema, caused by a spore forming microorganism, Nosema apis, which invades the digestive tract is a good example. Unfortunately, a new variation of the disease, Nosema ceranae, has completely disrupted the thinking about this disease and its effects on honey bee colonies.
Finally, a huge stress on honey bee colonies is the ever-present possibility that pesticides will affect colony behavior from killing colonies outright to more insidious non-lethal symptoms. These are becoming more important as more and more chemicals are being employed in Varroa mite control.
