(Paris) Fireflies like to shine at night, but struggle to mate when artificial light is too strong, a study revealed on Wednesday, which warns of the effects of light pollution on the decline of certain insect populations.
Posted at 7:12 p.m.
It is established that artificial lighting disturbs the behavior of many nocturnal animals in the search for food, orientation… And can even kill, like the moth flying around an electric light bulb which it confuses with the Moon, and eventually dies of exhaustion.
But it is difficult to predict the impact of increasingly intrusive nocturnal artificial light – its intensity has almost doubled over the past 25 years – on animals that have been accustomed to darkness for millennia: the species exposed will do they adapt, find refuge in darker skies, or decline?
To see more clearly, scientists have looked into fireflies, some species of which (there are more than 2000) are considered to be in decline according to the red list of threatened species of the IUCN (International Union for the Conservation of Nature). ), although data are lacking to assess this. At issue: habitat loss, pesticides… and light pollution.
Two researchers from the American Tufts University (Massachusetts) thus directly measured the effects of nighttime artificial light on the coupling of these bioluminescent beetles, and therefore their reproduction.
Emission of flashes
By conducting several experiments on the Photinus family, very present in North America: in adults, the diffusion of light (produced by chemical reaction in the abdomen) is used to find a partner during the mating season.
The male displays by emitting flashes, to which the female responds, also by blinking – a means of locating and recognizing females of the same species.
Observers equipped with LED bulbs posted themselves at the edge of the forest, at dusk, to imitate the signal of the females, under different lighting intensities. Result: 28 of the 29 lured males approached the “false” females attracting them in the dark, details the study published in Royal Society Open Science.
Same experiment in a field, on 34 pairs of another species of Photinus: the observer stationed sometimes shined a lamp on the patrolling male, sometimes let the pair form in the dark. Again, the artificial light – even low – significantly disrupted their ability to locate their halves.
The biologists reproduced the test in the laboratory, organizing meetings in variously lit enclosures. At natural dusk, 45% of pairs mated “successfully” — that is, until the release of spermatophore allowing reproduction. Ditto under weak artificial light (3 lux, the unit measuring the rendering of lighting). But at 30 lux, none of the 20 pairs had managed to mate.
The study concludes that light pollution necessarily plays on the decline of some species of fireflies – but not all – and recommends extending this type of research in order to better target efforts to protect endangered species.