High road mortality during female-biased larval dispersal in an iconic beetle

Abstract

Animals often disperse from one habitat to another to access mates or suitable breeding sites. The costs and benefits of such movements depend, in part, on the dispersing individuals’ phenotypes, including their sex and age. Here we investigated dispersal and road-related mortality in larvae of a bioluminescent beetle, the European common glow-worm, Lampyris noctiluca, in relation to habitat, sex and proximity of pupation. We expected these variables to be relevant to larval dispersal because adult females are wingless, whereas adult males fly when searching for glowing females. We found that dispersing glow-worm larvae were almost exclusively females and close to pupation. The larvae were often found on a road, where they were able to move at relatively high speeds, with a tendency to uphill orientation. However, each passing vehicle caused a high mortality risk, and we found large numbers of larvae run over by cars, especially close to covered, forest-like habitat patches. In contrast, adult females in the same area were most often found glowing in more open rocky and grassy habitats. These findings demonstrate an underappreciated ecological strategy, sex-biased dispersal at larval phase, motivated by different habitat needs of larvae and wingless adult females. The results are also consistent with roads being an ecological trap, facilitating dispersal and presumably females’ signal visibility but causing severe larval mortality just before the reproductive stage. Hence, in addition to the previously recognised threats of urbanisation, even low traffic volumes have a high potential to negatively affect especially females of this iconic beetle. Significance statement Animals sometimes need to move from one habitat to another to find mating partners or breeding sites. We found this need to result in strongly female-biased larval dispersal in the European common glow-worm, a beetle known for the glow of wingless females that attract flying males to mate. Female larvae moving between habitats often used a road or trail but perished in high numbers when run over by cars. Hence, roads are likely to be ecological traps for the female glow-worm larvae, attracting them during dispersal, but causing grave mortality. The sex-biased larval dispersal, demonstrated in this study, is a poorly known ecological strategy that was found to be very risky in a human-modified landscape.

Blinded by the Light: Artificial Light Lowers Mate Attraction Success in Female Glow-Worms (Lampyris noctiluca L.)

“…The common glow-worm is widespread in Flanders and is found in open forests and forest edges. During the day, female larvae search for vegetation bordering open spaces where they will later pupate [25]. This location will then remain their displaying site until they have mated [16].…”

The duration of artificial light defines sexual signalling in the common glow-worm

“…Glow-worms and other fireflies face many anthropogenic threats (Lewis et al 2020), including climate change, pesticides, habitat fragmentation, road mortality, and pollution (including artificial light) (Lewis et al 2020;Lehtonen et al 2021). Our finding that extended exposure to artificial light causes female glow-worms to cease glowing suggests that glow-worm reproduction (especially mate searching) would benefit from minimisation of the period of time that an artificial light is turned on, easing the negative anthropogenic impact on these beetles.…”

Plant growers’ environmental consciousness may not be enough to mitigate pollinator declines: a questionnaire-based case study in Hungary

“…Theodorou et al 2020), can also act as ecological traps (e.g. Campioni et al 2022; Lehtonen et al 2021) for insects in other cases. Indeed, although home gardens lure insect pollinators, pesticides are used in many of those gardens, contaminating the nectar and pollen of flowers (Nicholls et al 2018) which, in turn, can have deleterious effects on pollinators’ fitness.…”

“…Theodorou et al 41 ), can also act as ecological traps (e.g. Campioni et al 79 ; Lehtonen et al 80 ) for insects in other cases.…”