Exposure to constant artificial light alters honey bee sleep rhythms and disrupts sleep

Abstract

Artificial light at night (ALAN) is known to create changes in animal behavior in some invertebrates and vertebrates and can result in decreased fitness. ALAN effects have not been studied in European honey bees (Apis mellifera), an important pollinator. Colonies can be exposed to ALAN in swarm clusters, when bees cluster outside the nest on hot days and evenings, and, in limited cases, when they build nests in the open. Forager bees maintained in incubated cages were subjected to constant light or dark and observed with infrared cameras. The bees maintained a regular sleep pattern for three days but showed a shift on the fourth day in the presence of continuous light. Bees under constant light demonstrated a 24.05-hour rhythm, compared to a 23.12-hour rhythm in the dark. After 95 hours, the light-exposed bees slept significantly less and experienced significantly more disturbances from their peers. They also preferred to sleep in the lower portion of the cages, which had lower light intensity. These findings suggest that ALAN can disrupt honey bees sleep patterns, which may have implications for their behavior and overall colony health.