Transmission of Israeli acute paralysis virus through brood care in honey bees

Israeli acute paralysis virus (IAPV) is a major stressor for honey bees worldwide. Similar to other viruses, IAPV is vectored by the Varroa mite, and can be transmitted horizontally between adult bees through contact with infected bees or substances. However, compared to other honey bee viruses, the transmission pathways of IAPV inside a colony are less studied, particularly at the “worker-to-larva” interface. The likelihood that brood care is an important route of transmission for IAPV is high—not only for transmission between workers and larvae, but between workers as well. During brood care, several workers interact and contact each other both directly and indirectly through depositing diet while tending to a larva. IAPV has been detected in royal jelly and other components of the larval honey bee diet, but the susceptibility of the larvae to IAPV and the overall risk of transmission from an infected worker to a larva is understudied, as is the potential social immune response to prevent virus transmission. We performed a series of experiments to investigate the exposure of honey bee larvae to IAPV as a result of nursing from infected workers, including investigating the brood care behavior of infected workers towards a healthy larva. A more thorough understanding of transmission between workers and larvae can illuminate some aspects of how IAPV, without the presence of vectoring mites, can spread throughout a colony.