Читать книгу Honey Bee Medicine for the Veterinary Practitioner - Группа авторов - Страница 48

Group living in insects with its consequent division of labor, cooperative care of brood, and the overlap of more than a single generation in time and space are the hallmarks of the superorganism. Insects living within a coordinated framework, where tasks are divided among different bee castes and communication networks are compartmentalized in a confined space, are susceptible to the spread of disease from one individual to another. Likewise, their strict control of the nest cavity environment necessary to maintain the stable temperatures for brood care can be compared to a pathogen incubator. The group living of honey bees predisposes the individuals and the entire organism to epidemics. Fortunately, honey bees and other social insects have evolved highly adaptive behaviors that range from “constitutive” (aka prophylactic) to “inducible” (aka activated) responses that help prevent disease (Simone‐Finstrom 2017). Behaviors that reduce or eliminate pathogen exposure or pest infestation at the level of the superorganism are collectively known as social immunity.

One of the advantages of a social (or group) response to preventing or actively eliminating an infection by a parasite or pathogen in honey bee(s) is a coordinated response from the colony. By doing so, the individual bee is able to conserve resources that it would otherwise expend on maintaining and delivering an individual response. The immune function of individual honey bees is costly and expressed to a lesser degree than in asocial insects; indeed, the mapping of the Apis mellifera genome revealed a surprising lack of immune specific genes (Evans and Pettis 2005; Simone et al. 2009). This does not mean that individual honey bees lack discrete methods for disease protection entirely. Like other insects, honey bees have a hard chitinous exoskeleton that protects against pathogen entry, possess hemocytes that can phagocytize foreign invaders (though they lack memory cells and any ability to produce protective antibodies like vertebrates), remove themselves from the colony when sick or dying, recruit specialized members to perform dangerous biosecurity tasks as guards and undertakers, and even mummify pests too large to carry out of the hive.

In his comprehensive review of social immunity in honey bees, Simone‐Finstrom (2017) described the colony level adaptations for health in a continuum from prophylactic to activated: polyandry, task allocation, transfer of compounds and microbiota, resin use, allogrooming, hygienic behavior, social fever, and absconding. On the one extreme, diverse genes made possible by multiple matings and the compartmentalization of honey bee societies offer fixed preventative measures for health. The diversity that comes from numerous patrilines is linked closely to colony vigor and disease resistance and, once a queen mates, the colony's diversity (and thereby the protective alleles coding for disease protection) can only be changed by requeening. Likewise, the social structure of the honey bee colony, with its separation of castes, offers an important first line of defense against infectious disease since castes are separated in both time and space. Yet, the allocation of tasks is rarely altered by pathogen exposure.

On the other extreme, both social fever and absconding are actions taken by honey bees predominantly as a consequence of exposure to a pathogen and represent specific actions to combat the agent. Those social immune strategies located in‐between on the continuum may offer both prophylactic and treatment modalities; for example, the collection of resins can be preventative when bees seal their nest cavity in a complete protective “propolis envelope” or resin gathering can be activated by a specific pathogen as a kind of “self‐medication.” In our overview of social immunity, we will focus on just three of these traits: allocation of tasks with compartmentalization, use of compounds with antimicrobial actions – both bee‐derived and plant‐derived, and social fever. The miticidal actions of grooming and hygienic behavior are covered in detail elsewhere in this book on chapters about wild colony health, the biology of the varroa mite, and queen breeding for mite resistant honey bees.