Historical behavioural data disentangle evolutionary and environmental drivers of recent declines in insect...

Entomologists monitor insect population trends by surveying individuals attracted to artificial lights at night with the assumption that flight-to-light behaviour is fixed. However, emerging data suggest that entomological light traps are rapidly losing efficacy relative to other trap types, and the dramatic growth in anthropogenic light pollution over the past century has been identified as a probable cause. To investigate whether decades of strong selection against a conspicuously maladaptive behaviour have decreased insect attraction to light and compromised light trapping as a survey method, we compared the light attraction of urban and rural Helicoverpa zea (Boddie) corn earworm moths with historical behavioural records from 1967. Our results suggest that the flight-to-light response has remained relatively constant over time but may be strongly influenced by environmental visual clutter even in seemingly dark habitats. These findings call into question the use of light traps in long-term surveys, as the darkness within which they operate is rapidly deteriorating.