Abstract
Social immunity forms an essential part of the defence repertoire of social insects. In response to infestation by the parasitic mite Varroa destructor and its associated viruses, honey bees (Apis mellifera L.) have developed a specific behaviour (varroa-sensitive hygiene, or VSH) that helps protect the colony from this parasite. Brood cells heavily infested with mites are uncapped, the brood killed, and the cell contents removed. For this extreme sacrifice to be beneficial to the colony, the targeting of parasitized brood for removal must be accurate and selective. Here we show that varroa-infested brood produce uniquely identifiable cues that could be used by VSH-performing bees to identify with high specificity which brood cells to sacrifice. This selective elimination of mite-infested brood is a disease resistance strategy analogous to programmed cell death, where young bees likely to be highly dysfunctional as adults are sacrificed for the greater good of the colony.
Highlights
Honey bees (Apis mellifera L.) are cavity-nesting eusocial insects living in large colonies of around 40,000 sterile workers, a single fertile queen and, during the reproductive season, a few thousand males
By comparing the characteristics of individual brood targeted for removal by varroa-sensitive hygiene (VSH) behaviour (TA) with those of age-matched brood from adjacent varroa-infested but non-targeted (NT) cells and non-infested (NI) cells, this study suggests how adult bees choose which-pupae to sacrifice
The VSH behaviour observed in this study was performed by healthy bees on highly varroa-infested brood frames
Summary
Varroa destructor Infested Brood received: 06 January 2016 accepted: 15 April 2016 Published: 03 May 2016. Social immune management of the capped brood phase acquires special significance, as it represents a potential haven for pathogens and parasites seeking to avoid detection and removal elsewhere This is the context that has allowed the recently acquired, exotic parasite Varroa destructor to become the main pathogenic threat facing honey bee colony survival worldwide[8]. Some A. mellifera populations that naturally survive varroa infestation without treatment[12,13,14], implying that the combined social and individual defence mechanisms of A. mellifera are sufficiently plastic to adapt to new threats such as varroa One such adapted social defence is varroa-sensitive hygiene (VSH), which involves the specific detection and removal of varroa-infested (pre)-pupae[15]. By comparing the characteristics of individual brood targeted for removal by VSH behaviour (TA) with those of age-matched brood from adjacent varroa-infested but non-targeted (NT) cells and non-infested (NI) cells, this study suggests how adult bees choose which (pre)-pupae to sacrifice
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