An article in American Bee Journal (June, 1993, pp. 431-434) by Jost Dustmann discusses the natural defense mechanisms protecting the health of the honey bee. It asks a provocative question: when is a social organism like the bee colony sick? The presence of pathogens, the article continues, in a colony, single bees, food or wax does not mean a colony is sick. Only when the number of diseased or dead bees, larvae or pupae exceeds a certain limit and normal functioning of the colony is disturbed, is a colony deemed sick. A small loss of infected bees and individuals in developmental stages is necessary for any healthy colony.
The article discusses ten main defense mechanisms honey bees have against diseases and pests:
1. Cleaning or grooming behavior of adults. Some call this “hygienic behavior.” It is the basis for several breeding programs in the U.S. This pattern includes: (a) single infected bees reacting quickly by dying soon and removing themselves as a source of infection and/or (b) sister bees quickly identifying abnormal (diseased) individuals (adults, larvae and pupae) and eliminating them from the population. Hygienic behavior is shown to be effective against American foulbrood, nosema, chalkbrood, sacbrood and paralysis. The article also indicates that it will probably be involved in resistance to Varroa mites in European bees as has been observed in Asian species, Apis cerana.
2. Quickly regenerating losses of population. This is extremely effective as removal of diseased individuals can be compensated for in a short time. The ability to replace bees rapidly generally outstrips even the greatest current threat to populations, the Varroa bee mite.
3. Continuous rotation of bee generations. Brood followed by adults followed by brood is analogous to crop rotation in commercial agriculture, where growing of one crop is often followed by sowing another. The article suggests a good example of this is tracheal mite infestation, which cannot keep up with replacement of bees by a colony in normal times. There is also evidence of active movement of mites into older bees. However, when older bees live longer, the mites may get the upper hand.
4. Swarming. A major defense is building new wax combs after bees swarm from their old colony. This appears to be a predominant strategy of Africanized honey bees, which not only swarm, but also abandon (abscond from) their nests. Beekeepers can artificially mirror this activity by renovating combs periodically.
5. Restricting disease to either larvae or adults. This strategy ensures that if larvae are diseased, adults are not and vice versa. Both stone brood and Varroa are exceptions to this rule.
6. Control of fertility and population control. More in evidence in Varroa infestations, the mite’s preference for drone brood deflects parasitization away from workers. In addition, the heavy cappings on affected drone brood, if left intact, ensure fewer mites will emerge.
7. Immune reactions. Observed in single adult bees, this has not been shown for the colony as a whole, but is a reasonable hypothesis Bactericidal molecules (peptides) are formed in individual bees and consumption of foreign materials (phagocytosis) by blood (hemolymph) cells has also been observed.
8. Stinging and biting. The first is self-evident. Biting has been shown to be a defense mechanism against Varroa, but found at low levels in European bees. New research is revealing that biting is in fact more important than at first realized.
9. Proventriculus and peritrophic membrane. The former structure prevents entry of foreign organisms (bacteria, pathogens) from the crop or honey stomach into the digestive system. The latter lines the digestive tract, protecting it from rough materials and also preventing entry of bacteria and fungi into the hemolymph.
10. Antibiotic substances. An extremely important aspect of the honey bee’s defenses, these chemicals can be found in honey (called “inhibine”), stored pollen and propolis (flavonoids, terpenes). These substances have also been implicated in human health concerns, including the use of diluted honey as a surgical dressing and consumption of propolis as preventative medicine.
The article concludes with another question: How can the beekeeper manage bees without interfering with the above natural strategies? There are five recommendations:
1. Selecting and breeding bees that have the necessary defense mechanisms already in place. Controlled mating is seen as essential.
2. Ensuring the environment provides enough of the right food for bees. If not, then the beekeeper must feed both carbohydrate (sugar) and protein (pollen substitute/supplement).
3. Determining the beehive is the right size with reference to colony size and management practices. Establishing artificial swarms that build new combs and uniting young colonies with older ones established the year before ensure rotation of bees and wax. Routinely replacing (renovating) old combs is something every beekeeper should consider. Splitting hives, which also produces new queens is becoming more the norm
4. Keeping bees without using drugs. In general, the article concludes that medical treatment of a colony will interfere with the natural defense mechanisms discussed above. This is especially true for antibiotics, which cannot eradicate infections, but only mask symptoms, leading to sometimes huge reservoirs of disease ready to break out at any moment. One exception to this, however, is the use of a registered pesticide to control Varroa, sometimes an absolute necessity at the present time in many North American apicultural situations.
Finally, many colonies take care of themselves whether the beekeeper takes action or not. See what contributor Rusty Burlew found out via inadvertent “let alone beekeeping.”