Chronic heat stress disrupts foraging motivation in honey bees

Abstract

Pollinator mortality is a global concern linked to climate change; however, the complex responses underlying heat stress in honey bees are not yet fully understood. This study investigated the impact of chronic heat stress on honey bee appetitive motivation and related physiological processes that are essential for colony functioning. From June to October 2022 and April to October 2023, bees were exposed to 25°C (Group 25) and 35°C (Group 35) in controlled environments, with a Group Control kept under natural conditions. We evaluated sucrose responsiveness as an appetitive indicator, colony performance in late summer, four physiological traits, and eleven molecular markers. Nine genes were heat-sensitive, including those linked to maturity, aging (AmMblk-1, Amfor), and cognition (JHAMT, AmOctaR1). Foragers from Group 35 showed reduced sensitivity to low-sucrose solutions, potentially impairing food collection. This behavioral deficit likely contributed to poor honey stores and reduced colony development. Our findings suggest that chronic heat stress can impair honey bee foraging motivation and efficiency, posing a risk to colony health. These results underscore the broader ecological consequences of rising global temperatures for pollinators.