Читать книгу Honey Bee Medicine for the Veterinary Practitioner - Группа авторов - Страница 52

The idea that non‐human animals can self‐medicate – that is, use organic compounds to clear an infection or reduce its symptoms – was long thought to be limited to vertebrates since it was presumed that it required learning (de Roode et al. 2013). However, we now know that self‐medication or “zoopharmacognosy” is widespread in the insect world, in part because insects utilize a wide variety of organic compounds and have evolved methods to medicate their relatives, offspring, or even societal members. Given there are a variety of reasons why an animal might consume an organic substance independent of improving its own health or that of its kin, true self‐medication has a strict definition: the organism must intentionally seek out the compound, the compound must harm the parasite, the compound must benefit the host, and finally, its use must come with a cost to the host if consumed in the absence of an infection (Abbott 2014).

Honey bees exhibit self‐medication both as a way to prevent infection and to treat an acquired infection. While most insects consume organic compounds to protect their own health or that of their offspring, eusocial honey bees collect resins to treat the entire colony rather than the individual bee, a form of mass medication. Simone‐Finstrom and Spivak (2012) observed that honey bees increased their resin foraging in response to exposure to the chalkbrood fungus, A. apis. In their study, rates of pollen collection declined while resin collection increased after honey bees were challenged with chalkbrood. Since chalkbrood is a disease of larvae and not adult bees, the increase in collection of resins in response to a fungal pathogen is a marvelous example of social immunity in which the colony, rather than the individual bee, is the beneficiary of the adaptive behavior (Simone‐Finstrom and Spivak 2012). Curiously, the bacteria causing American foulbrood and another fungus, Metarhizium, failed to elicit increased resin foraging in their investigation.

Pollen plays a key role in brood rearing, worker bee lifespan, and bee resistance to pathogens. In particular, pollen and protein availability influence hypopharyngeal gland development in worker bees and an abundance is associated with lowered infection titers with deformed wing virus (DeGrandi‐Hoffman et al. 2010). Although not a form of self‐medication since bees do not increase pollen collection in response to infection, a pollen rich diet has been shown to provide protective benefits against a variety of pathogens, including the Varroa mite (Annoscia et al. 2017). In particular, the apolar fraction of pollen (that portion of pollen especially high in fatty acids, hydrocarbons, and sterols, and distinguishable in the laboratory from the polar fraction) appears to provide a dietary protective measure against disease. In the case of Varroa mites, the adults penetrate the bee cuticle and increase water loss, feed on the bee's fat body creating a negative energy balance, and vector viral diseases. Pollen is protective by providing a source of hydrocarbons for cuticle integrity, the unsaturated fatty acid component of pollen shows antibiotic activity, and pollens enhance immune function. The authors conclude that in bees infested with V. destructor, access to a pollen‐rich diet increases lifespan and can compensate for the negative effects of the mite (Annoscia et al. 2017). Bumble bees (Bombus impatiens) are known to alter their foraging patterns based on the quality of the nutritional resource, with high Pollen:Lipid ratios of highest attraction (Vaudo et al. 2016). Likewise, the secondary metabolites in floral nectar (alkaloids, teropenoids, and glycosides) have been shown to reduce bumble bee parasite loads (Richardson et al. 2015). Such observations confirm suspicions that changes in bee forage, particularly in agricultural dominated landscapes or in migratory beekeeping practices, likely contributes to colony declines. The important message for the bee doctor from all this research is that colony nutrition is ultimately connected to colony health and that the role of the veterinarian in helping the beekeeper manage disease should always include a thorough evaluation of colony nutrition, including review of local bloom calendars, hive pollen stores, and the use of protein supplements.