A model of infection in honeybee colonies with social immunity

Abstract

Honeybees (Apis mellifera) play a significant role in the pollination of various food crops and plants. In the past decades, honeybee management has been challenged with increased pathogen and environmental pressure associating with increased beekeeping costs, having a marked economic impact on the beekeeping industry. Pathogens have been identified as a contributing cause of colony losses. Evidence suggested a possible route of pathogen transmission among bees via oral-oral contacts through trophallaxis. Here we propose a model that describes the transmission of an infection within a colony when bee members engage in the trophallactic activity to distribute nectar. In addition, we examine two important features of social immunity, defined as collective disease defenses organized by honeybee society. First, our model considers the social segregation of worker bees. The segregation limits foragers, which are highly exposed to pathogens during foraging outside the nest, from interacting with bees residing in the inner parts of the nest. Second, our model includes a hygienic response, by which healthy nurse bees exterminate infected bees to mitigate horizontal transmission of the infection to other bee members. We propose that the social segregation forms the first line of defense in reducing the uptake of pathogens into the colony. If the first line of defense fails, the hygienic behavior provides a second mechanism in preventing disease spread. Our study identifies the rate of egg-laying as a critical factor in maintaining the colony’s health against an infection. We propose that winter conditions which cease or reduce the egg-laying activity combined with an infection in early spring can compromise the social immunity defenses and potentially cause colony losses.

Honey bees increase social distancing when facing the ectoparasite Varroa destructor

“…At the core of the society, an excess of compartmentalization, by avoiding interactions with infected nestmates, might lead to social disruption and a dramatic loss of work force. Although our study does not provide evidence to support either of the two hypotheses (caregiving or ergonomic optimization), it shows the importance of investigating the variation in social immunity strategies and their interaction across different levels (e.g., cohort age) and contexts in insect societies (46)(47)(48).…”

Glucosinolate Bioactivation by Apis mellifera Workers and Its Impact on Nosema ceranae Infection at the Colony Level

“…Fully developed colonies definitely represent a situation not easily comparable to small groups of bees of the same age confined in cages and reared in an incubator. The dose administered to fully developed colonies is shared among a large number of the members of the superorganismic group by trophallactic exchanges [ 72 ] and diluted with other feeding sources coming from the available floral resources or from nest stores.…”

Pathogens Spillover from Honey Bees to Other Arthropods

“…Nonetheless, the global picture is certainly far from complete, since data may misrepresent the actual distribution and gaps remain in our understanding of both epidemiological features and invasion dynamics of many pathogens [ 12 , 20 , 21 , 22 , 23 , 24 , 25 ]. Apis mellifera is known to share pathogens with bumblebee species, including viruses, bacteria, fungi and protozoa [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. After acting as incidental hosts, western honey bees may become the primary maintenance host, as occurred in the cases of Nosema ceranae , Crithidia bombi , and Apicystis bombi [ 35 ].…”