Bee Self Defence- Hygienic Behaviour
Originally printed in the October 2014 issue of the Australian Bee Journal
Humans and Bees
Humans have had a relationship with honey bees (Apis mellifera) for a long time. From the earliest honey hunters to beekeepers managing apiaries, we have used their honey and propolis as food and medicine and their wax for industry. Now we rely on them to pollinate our intensive food system essential to feeding the world’s people. Only healthy honey bees can grow colonies to produce profitable quantities of hive products and provide pollination services that are essential to our lives.
Honey Bee Self Defense
Honey bees colonies can be thought as a super organism, each bee having a role and contributing to the greater fitness of the whole. As such, these super organisms have evolved for millions of years, developing behavioural and biological defenses against pests and diseases, keeping the colony healthy and productive. By understanding bee self defense behaviours and biological processes beekeepers can use both breeding and management decisions to optimize honey bee health.
This article provides a background on hygienic behaviour, an important bee self defense behaviour. It is the first of a series of articles on self-defense traits aimed at helping beekeepers maintain optimum health in their apiaries.
Hygienic behaviour is a heritable genetic trait and a specific type of nest hygiene triggered by smell where 15-18 day old workers can detect, uncap, and remove dead or diseased brood from the nest before the disease enters into a transmittable stage (Arathi et al. 2000, Masterman et al. 2001). Some bees are able to detect diseased brood shortly after it is infected and remove it before the pathogen becomes contagious. Slow removal of diseased brood (after it is contagious) may actually aid the spread of disease in the nest.
Two equally beautiful brood frames. The frame on the left is from a hygienic colony whereas the frame on the right is from a non hygienic colony
Hygienic behaviour was first noted in the 1930’s during efforts to determine if some honey bee colonies were resistant to American Foulbrood (ABF) caused by the bacteria Paennibacillus larvae. Interest in this behavioural trait continued through the 1960 and 1970’s as a mechanism for resistance to AFB. However, with the advent of sulfa drugs and antibiotics used to treat AFB, research was not sustained. In the late 1950’s Walter Rothenbueler coined the term “hygienic behaviour” while studying the heritability of the trait.
During the past 30 years in most of the world, AFB developed resistance to a commonly used chemical, oxytetracyclene (OTC), chalkbrood posed serious negative effects on colony health and Varroa emerged as a major threat to most of the world’s honey bee populations. As bee pests and diseases either developed resistance to chemicals, or the effective chemicals used have shown to have negative effects on honey bee health, beekeepers and researchers are again examining bee’s own self defense mechanisms.
In 1941 A.W. Woodrow (USDA in Laramie Wyoming, USA) fed sugar syrup inoculated with p. larvae spores to experimental colonies and discovered that some colonies removed infected brood before it formed contagious spores (Spivak and Gilliam 1998, I). In fact, the faster the diseased brood was removed, the fewer additional larvae were infected. The most rapid removers showed no signs of AFB infection even through spores were found in brood cells and honey. Those rapid removers were resistant to AFB (Sturtevant 1953 as reviewed in Spivak and Gilliam 1998, I).
Chalkbrood (caused by the fungus Ascosphaera aphis) was discovered in the USA in 1968 in California and spread rapidly across the North America. When USDA researchers Steve Taber and Martha Gilliam found chalkbrood in Arizona, they began looking closer at the pathology of the fungal infection.
They observed that some colonies removed larvae infected with chalkbrood within 24 hours. Through subsequent studies Gilliam and coworkers determined it was possible to breed for resistance to chalkbrood. Hygienic behaviour was found to be the primary factor that led to chalkbrood resistance however, there are other factors that help a colony resist the infection. Interestingly, “friendly” moulds and beneficial bacteria found in bee bread can inhibit A. apis growth (more information on beneficial microbes in a future article) (Spivak and Gilliam 1998, II).
Tests for selecting for hygienic behaviour were devised and refined. Colonies were presented with a section of frozen brood and the time to uncap and remove the dead pupae was monitored. Colonies that quickly removed dead frozen pupae were also colonies that showed resistance to chalkbrood. This process showed that using freeze killed brood could serve as a test to gauge the colony’s propensity for hygienic behaviour and thus resistance to chalkbrood.
When faced with Varroa infestation, colonies bred for hygienic behaviour have been observed to remove mite infested pupae, interrupting the mite’s reproductive cycle. However, at low infestation rates, the chemical cues may not be strong enough for the hygiene bees to detect the parasitized larvae. Only at high infestation rates (two or more mites per brood cell) is the pupae damaged enough to alert the hygiene bees (Boecking 1992). But if the colony is faced with an infestation that severe, the colony is probably beyond saving. Hygienic behaviour alone is not the silver bullet for Varroa tolerance.
Breeding for Hygienic Behaviour
Breeding for hygienic behaviour is easily performed. It is being implemented worldwide in countries with substantive apicultural industries.
In populations of honey bees that have not been selected specifically for rapid hygienic behaviour, around 10% of the colonies will carry this trait (Spivak personal comm). From the research done in Australia on hygienic behaviour, just over 15% of tested colonies meet the requirement for rapid hygienic behaviour. These data demonstrate that Australian Honey bee stocks do exhibit rapid hygienic behaviour useful for combating diseases such as AFB and chalkbrood and pests such as future populations of Varroa. These stocks can be improved on with selective breeding.
Stock improvement: Selecting and Breeding for Hygienic Behaviour
Arathi, H. S., and Marla Spivak. “Influence of colony genotypic composition on the performance of hygienic behaviour in the honeybee,< i> Apis mellifera L.” Animal Behaviour 62.1 (2001): 57-66.
Boecking, O., and W. Drescher. “The removal response ofApis mellifera L. colonies to brood in wax and plastic cells after artificial and natural infestation withVarroa jacobsoni Oud. and to freeze-killed brood.” Experimental & applied acarology 16.4 (1992): 321-329.
Masterman, R., et al. “Olfactory and behavioral response thresholds to odors of diseased brood differ between hygienic and non-hygienic honey bees (Apis mellifera L.).” Journal of Comparative Physiology A 187.6 (2001): 441-452.
Spivak, M. and M. A. Gilliam. “Hygienic behaviour of honey bees and its application for control of brood diseases and varroa.” Part I Bee World 79.3 (1998): 124-134.
Spivak, M. and M. A. Gilliam. “Hygienic behavior of honey bees and its application for control of brood diseases and varroa.” Part II Bee World 79.4 (1998): 169-186.