OSAKA, Japan – A new study shows how increases in nighttime lighting (light pollution) and heat from urban areas disrupt insects’ dormancy.
“The study examines a species of meat fly called Sarcophaga similis, but the results could be applicable to any species that rely on predictable environmental signals for biological processes such as growth, reproductive behavior, sleep and migration,” said Assistant Professor Ayumu Mukai of Setsunan University and lead author of the Study. In collaboration with Professor Shin Goto from Osaka City University, her results were published in the Royal Society Open Science.
A common way to study the environmental impacts of urbanization is to study changes in the life cycle of species in the city and surrounding areas. Urban warming and artificial light at night are two of the most important factors. Since urban warming can increase surface temperatures between 5 – 9 ° C, species with lower critical thermal optima, ie biological processes such as growth and development that take place at lower ambient temperatures, are disproportionately affected. Due to large variations throughout the day and year, temperature can be an unreliable indicator for species to determine when to sleep, breed, migrate, etc. Photoperiodism. More nighttime light can disrupt an insect’s photoperiodism, but few studies have focused on the effects of urban warming and artificial light at night on insects in their natural habitat.
“Understanding the conditions that urbanization brings for insects, where they actually live, would be a big step forward in mitigating negative impacts,” said Shin Goto. To understand this, the team conducted experiments indoors and outdoors. Since S. similis typically goes into hibernation in autumn, the laboratory hibernation was induced in flies below two average October temperatures (20 ° C and 15 ° C) with different illuminance levels in order to mimic light urban to dark rural areas. They found that the percentage of flies hibernating decreased from 15 ° C to 20 ° C with increasing lighting and temperature – suggesting that the higher temperatures in urban areas are associated with higher nighttime lighting.
In the field, the team measured when the insects went into hibernation at two locations in the city: at one location with night lighting of around 0.2 lux (the brightness of a full moon on a clear sky) and another with night lighting of around 6 lux, which corresponds to a residential area or a street at night. In locations with dark nights, most flies go into hibernation between October and November, while in locations with increased night light they do not hibernate until after November. The team also compared urban areas with an illuminance of around 0.2 lux with rural areas of almost 0 lux. The proportion of flies hibernating in rural areas increased from late September, about 3 weeks earlier than their urban ones Counterparts. In the cities, too, the temperatures were 2.5 ° C higher, which is believed to be the cause of the delay in hibernation.
While these results suggest that the nighttime lighting that supports our daily lives disrupts insect seasonality, “urban environments are complex, with nighttime lighting and temperatures that vary within the same neighborhood and between different cities,” emphasized Ayumu Mukai: “And our work on a single meat fly does not illuminate the photoperiodic response of other insects.”
To understand the extent to which our cultural life affects other organisms, Shin Goto continued: “Future studies with a variety of insect species in different locations in cities with different climates would clarify how light pollution and urban warming affect the seasonal adaptation of insects affect ”
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