Environmental influences on the bioluminescence display of the glow-worm, Arachnocampa flava (Diptera: Keroplatidae)

Glow-worms are the larvae of fungus gnats that use bioluminescence to lure night-flying insects to their webs. They are found in still, humid environments such as rainforest gullies, the vicinity of waterfalls or inside caves. Arachnocampa flava is endemic to south-east Queensland where it is the focus of night-time tourism at a number of subtropical rainforest locations. For management of tourist populations as well as understanding the natural dynamics of the bioluminescence display, previous studies of A. flava used photographic imaging or quadrat-based counts to assess the number of larvae glowing. Here, time-lapse digital photography with an SLR camera is employed in a rainforest gully to image a glow-worm colony at 10 min intervals. Recordings took place between April and December of 2010. Blocks of continuous recording lasted 13-35 continuous days. This sampling frequency revealed the nightly bioluminescence intensity profile and the influence of some environmental conditions. On nights without rainfall, larvae initiated glowing soon after dusk, rapidly rose to a peak intensity and then progressively decreased their intensity through to dawn when they douse in response to approaching dawn. Bioluminescence output increased substantially on nights when rainfall was recorded. Use of a tipping-bucket rain gauge at the site showed that larvae increased their intensity and the number glowing increased immediately when rain began falling. Moonlight around the time of a full moon inhibited larval bioluminescence output. The time-lapse photographic method proved to be a useful monitoring tool that has revealed correlations between climate and season and the intensity of the glow-worm display