Do you ever have a hard time falling asleep if there is light streaming into your bedroom, which you cannot block out? You could say that your biological sleep cycles are disrupted by uninvited light. The same thing happens to animals and plants, particularly as artificial light pollution at night (e.g. city light glow, streetlamps etc.) has been increasing since the 19th century. Lots of living things use natural light as a cue for biological activity, such as feeding and mating. In addition, some animals that are usually active during the day are now becoming active at night because of artificial light. Elisa Gomes and colleagues at the University of Lyon, France, were particularly interested in figuring out if artificial light impacts the feeding and mating rituals of a parasitic wasp, Venturia canescens. A previous study by Gomes showed that this wasp species, which is usually active during the day, also became active at night when exposed to artificial light. Knowing this, Gomes wondered whether artificial light might lead the wasps to feed and lay eggs at night, instead of during the day, as well as altering their lifespans.
To test this, Gomes housed the wasps in plastic boxes at a constant temperature (25°C) with periodic access to food (sugar water) and Mediterranean flour moth larvae, the hosts upon which the parasitic wasps lay their eggs. The team then recreated the natural light patterns of 12 h of light followed by a dark night. While some of the insects experienced low intensity light pollution overnight, comparable to city skyglow, others had their nights disturbed by high intensity light (comparable to a streetlamp). Over a 2-week period, the team monitored the food eaten by the wasps and counted how many eggs they laid in the moth larvae. The researchers also recorded when the wasp offspring emerged from the parasitized moths to determine if artificial light impacted the wasp larvae's development.
Gomes found that the wasps fed more and laid more eggs at night when exposed to nocturnal light pollution. The wasps also lived longer when the artificial light that they experienced at night was more intense, which Gomes speculates might be because the wasps had more time to feed. Despite laying more eggs in artificial light at night, the wasps did not produce more eggs over the entire course of their lifetime. This may have been because the wasps that were experiencing nocturnal light pollution laid fewer eggs during the day. Finally, older wasps that had been exposed to artificial light at night laid eggs that developed faster than eggs laid in total darkness. However, this did not seem to impact the offspring's ultimate development – they grew to be the same size as the offspring produced by parents that experienced complete darkness at night, which developed slower.
Gomes suspects that the offspring exposed to artificial light may have other physiological differences caused by nocturnal light pollution, which were not tested in this study. She also highlights several factors that need to be investigated further, such as what happens when the wasps experience the temperature falls that occur naturally at night. It is also not known if these wasps are sensitive to different colours or shades of artificial light, which could be an intriguing direction for future research. Ultimately, it is clear that artificial light alters the wasp's behaviour, although it remains a mystery whether this is for better or worse.
