Acute ozone exposure impairs detection of floral odor, learning, and memory of honey bees, through olfactory generalization

Air pollution stemming from human activities affects the environment in which plant and animal species live and interact. Similar to primary air pollutants which are emitted, secondary air pollutants, such as tropospheric ozone (O-3) formed from nitrogen oxides, are also harmful to human health and plant physiology. Yet, few reports studied the effects of O-3 on pollinators' physiology, despite that this pollutant, with its high oxidative potential, likely affects pollinators behaviors, espe-cially the perception of signals they rely on to navigate their environment. Volatile Organic Compounds (VOCs) released by plants are used as signals by different animals. For pollination services, VOCs attract different insects to the flowers and strengthen these interactions. Here, we used the honey bee Apis mellifera as a model to characterize the effects of acute ex-posure to different realistic mixing ratios of O-3 (80-, 120-, and 200-ppb) on two crucial aspects: first, how exposed honey bees detect VOCs; and second, how O-3 affects these pollinators' learning and memory processes. With electroantennogram (EAG) recordings, we showed that increasing O-3 mixing ratios had a biphasic effect: an initial 25% decrease of the anten-nal activity when bees were tested directly after exposure (O-3 direct effect), followed by a 25% increase in activity and response when bees were allowed a two-hour rest after exposure (O-3 delayed effect). In parallel, during olfactory condi-tioning, increasing O-3 mixing ratios in both exposure protocols scarcely affected olfactory learning, followed by a decrease in recall of learned odors and an increase of response to new odors, leading to a higher generalization rate (i.e., discrimination impairment). These results suggest a link between O-3-related oxidative stress and olfactory coding dis-turbance in the honey bee brain. If ozone affects the pollinators' olfaction, foraging behaviors may be modified, in addition with a possible long-term harmful effect on pollination services.