Multiple Effects of Artificial Lighting at Night on Male Glow-worms' Mate Searching Behaviour

Artificial lighting at night (ALAN) has been identified as a driver of insect decline, disrupting their ecology, behaviour and physiology. Recent studies have begun to identify the mechanisms by which ALAN affects nocturnal insects but focus primarily on moths. In glow-worms (Lampyris noctiluca), population survival relies on males detecting and reaching the glow emitted by bioluminescent females at night. Despite evidence suggesting many deleterious effects of ALAN on their mating success, little is known about the behavioural mechanisms underlying those effects. Using a translational approach, we assessed males ability to detect and approach females, both in nocturnal conditions and under ALAN showing that males land near a female before walking towards it. Thus, males navigate through dense vegetation to find a mate. Males walking on a trackball were highly reliable in adjusting their course to rapid left to right shifts of a green LEDs mimicking females glow, reorienting in less than 1 second. Under ALAN, males reliability to detect the dummy female was significantly hindered, along with their speed, stamina and orientation. This indicates ALAN has multiple simultaneous impacts on the ability of males to reach females, impairing their mating with potentially severe consequences on glow-worms population survival.