Effects of artificial light on growth, development, and dispersal of two North American fireflies (Coleoptera: Lampyridae)

Living on the edge: urban fireflies (Coleoptera, Lampyridae) in Morelia, Michoacán, Mexico

Fireflies (Coleoptera, Lampyridae) are a globally threatened group of insects due to habitat loss and fragmentation, light pollution, climate change and pesticides. However, against all odds, some firefly populations persist in urbanized environments where all four of these factors are present simultaneously. In this work, we compiled several data sources to document the diversity of fireflies in the urbanized area of Morelia, characterize their current habitats, and determine the main stressors affecting these bioluminescent insects. We found seven genera and 26 species of fireflies (19 nocturnal, seven diurnal) associated with 32 urban, peri-urban and extra-urban areas; at least, 14 are new records for Michoacán, and the list for the state now includes nine genera and 41 species. Five additional sites were documented as extinction sites. We compared the characteristics of these five sites with those of the sites with extant populations. We found that in Morelia, fireflies are mainly associated with areas that have high to moderate proportions of vegetation cover, are near water bodies, have very gentle to moderate slopes, and are exposed to low levels of light pollution. In contrast, the extinction sites showed high proportions of artificial surfaces and high levels of light pollution. Because some fireflies are considered bioindicators of ecosystem integrity as they are associated to specific habitats, are highly diverse and due to their sensitivity to environmental changes, we consider that sites from Morelia's urban core and extinction sites show the highest levels of environmental degradation, threatening most fireflies and other insects living in the urban core with local extinction. At the same time, our results also suggest that implementing conservation strategies and sustainable planning for the urban development of Morelia in the short term could allow fireflies and other vital elements of the city's insect communities to persist for future generations. Restoration and conservation of green areas and nighttime environments are essential for biodiversity and human health, especially in intra-urban zones.

Behavioral responses of bioluminescent fireflies to artificial light at night

Bioluminescent insects have been the subject of scientific interest and popular wonder for millennia. But in the 21st century, the fireflies, click beetles, and cave glow-worms that brighten our nights are threatened by an unprecedented competitor: anthropogenic light pollution. Artificial lights can obscure the light-based signals on which these and other bioluminescent organisms rely to court mates, deter predators, and attract prey. In the following review we summarize a recent influx of research into the behavioral consequences of artificial light at night for firefly beetles (Coleoptera: Lampyridae), which we organize into four distinct courtship signaling systems. We conclude by highlighting several opportunities for further research to advance this emerging field and by offering a set of up-to-date lighting recommendations that can help land managers and other stakeholders balance public safety and ecological sustainability.

Artificial light impacts the mate success of female fireflies

Anthropogenic light pollution is a novel environmental disruption that affects the movement, foraging and mating behaviour of nocturnal animals. Most of these effects are sublethal, and their net impact on reproductive fitness and population persistence is often extrapolated from behavioural data. Without dedicated tracking of wild individuals, however, it is impossible to predict whether populations in light-polluted habitats will decline or, instead, move to shaded refuges. To disentangle these conflicting possibilities, we investigated how artificial light affects mating and movement in North American Photinus, a genus of bioluminescent fireflies known to experience courtship failure under artificial light. The degree to which artificial light reduced mate success depended on the intensity of the light treatment, its environmental context, and the temporal niche of the species in question. In the laboratory, direct exposure to artificial light completely prevented mating in semi-nocturnal Photinus obscurellus. In the field, artificial light had little impact on the movement or mate success of local Photinus pyralis and Photinus marginellus but strongly influenced mate location in Photinus greeni; all three species are relatively crepuscular. Our nuanced results suggest greater appreciation of behavioural diversity will help insect conservationists and dark sky advocates better target efforts to protect at-risk species.

Artificial light impacts the mate success of female fireflies

Anthropogenic light pollution is a novel environmental disruption that affects the movement, foraging and mating behaviour of nocturnal animals. Most of these effects are sublethal, and their net impact on reproductive fitness and population persistence is often extrapolated from behavioural data. Without dedicated tracking of wild individuals, however, it is impossible to predict whether populations in light-polluted habitats will decline or, instead, move to shaded refuges. To disentangle these conflicting possibilities, we investigated how artificial light affects mating and movement in North American Photinus, a genus of bioluminescent fireflies known to experience courtship failure under artificial light. The degree to which artificial light reduced mate success depended on the intensity of the light treatment, its environmental context, and the temporal niche of the species in question. In the laboratory, direct exposure to artificial light completely prevented mating in semi-nocturnal Photinus obscurellus. In the field, artificial light had little impact on the movement or mate success of local Photinus pyralis and Photinus marginellus but strongly influenced mate location in Photinus greeni; all three species are relatively crepuscular. Our nuanced results suggest greater appreciation of behavioural diversity will help insect conservationists and dark sky advocates better target efforts to protect at-risk species.

Costs and benefits of "insect friendly" artificial lights are taxon specific

The expansion of human activity into natural habitats often results in the introduction of artificial light at night, which can disrupt local ecosystems. Recent advances in LED technology have enabled spectral tuning of artificial light sources, which could in theory limit their impact on vulnerable taxa. To date, however, experimental comparisons of ecologically friendly candidate colors have often considered only one type of behavioral impact, sometimes on only single species. Resulting recommendations cannot be broadly implemented if their consequences for other local taxa are unknown. Working at a popular firefly ecotourism site, we exposed the insect community to artificial illumination of three colors (blue, broad-spectrum amber, red) and measured flight-to-light behavior as well as the courtship flash behavior of male Photinus carolinus fireflies. Firefly courtship activity was greatest under blue and red lights, while the most flying insects were attracted to blue and broad-spectrum amber lights. Thus, while impacts of spectrally tuned artificial light varied across taxa, our results suggest that red light, rather than amber light, is least disruptive to insects overall, and therefore more generally insect friendly.

Evaluating firefly extinction risk: Initial red list assessments for North America

Fireflies are a family of charismatic beetles known for their bioluminescent signals. Recent anecdotal reports suggest that firefly populations in North America may be in decline. However, prior to this work, no studies have undertaken a systematic compilation of geographic distribution, habitat specificity, and threats facing North American fireflies. To better understand their extinction risks, we conducted baseline assessments according to the categories and criteria of the International Union for Conservation of Nature (IUCN) Red List for 132 species from the United States and Canada (approximately 79% of described species in the region). We found at least 18 species (14%) are threatened with extinction (e.g. categorized as Critically Endangered, Endangered, or Vulnerable) due to various pressures, including habitat loss, light pollution, and climate change (sea level rise and drought). In addition, more than half of the species (53%) could not be evaluated against the assessment criteria due to insufficient data, highlighting the need for further study. Future research and conservation efforts should prioritize monitoring and protecting populations of at-risk species, preserving and restoring habitat, gathering data on population trends, and filling critical information gaps for data deficient species suspected to be at risk.

Ecological Corridor Construction Based on Least-Cost Modeling Using Visible Infrared Imaging Radiometer Suite (VIIRS) Nighttime Light Data and Normalized Difference Vegetation Index

Anthropic pressure is one of the main drivers of landscape change and biodiversity loss. Artificial nighttime light, which can affect species behavior, is an important human-induced threat to biodiversity, but it is often ignored in ecological connectivity research. To mitigate the adverse impacts of artificial lighting on biodiversity, this study integrates artificial nighttime light in landscape ecology and analyzes the influence of artificial nighttime light on landscape connectivity. A quantitative approach integrating nighttime light brightness from a Visible Infrared Imaging Radiometer Suite (VIIRS) with a normalized difference vegetation index (NDVI) from a Moderate-resolution Imaging Spectroradiometer (MODIS) is proposed to estimate the matrix resistance, which can identify the sensitive areas that are disrupted by nighttime light. It was found that the nightscape in the study area is significantly disrupted by nighttime light and the matrix resistance in the center of the study area significantly increases. Compared to the least-cost routes from the NDVI, the “dark” least-cost ecological corridors constructed using our approach apparently change in both location and distance. The corridors moved to the outer suburbs and rural areas, and the maximum increase in distance of the least-cost paths was 37.94%. Due to less disturbance from human activity and the maintenance of a pristine nightscape, “dark” ecological corridors can reduce the adverse effects of night lights and contribute to biodiversity. However, natural habitats have been greatly affected by nighttime light with the increase in global illumination, and it is essential that we improve public awareness of light pollution and formulate light-reduction policies and legislation.