Moth species becomes more sexually active when bathed in red light

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An Asian-Australian moth becomes more sexually active under red light than under another colour of light, or in dark conditions.

Dim red light appears to stimulate chemical changes in the antennae of male yellow peach moths (Conogethes punctiferalis), making them more sensitive to the smells emitted by nearby females. This increases their copulation rates, says Wei Xiao at Southwest University in Chongqing, China.

Xiao and his colleagues made the accidental discovery while running general behaviour studies on the moths, which invade orchards and spice farms across Asia and Australia.

To mimic natural light conditions in their laboratory, the scientists kept the lights on for 15 hours and turned them off for nine hours per day. When they needed to work with the moths during the hours of darkness, they turned on red lights because scientists generally assume that insects can’t see red and react negligibly to it, says Xiao.

However, his team realised that every time they turned on the red lights, the moths responded by laying more eggs. So the researchers decided to test the effects of red lights on mating.

They set up four cages, three of which were dimly lit by either red, white or blue light. The last was in complete darkness. Then they placed 30 male and 30 female moths in each cage.

They found that the moths in the ‘red’ cage mated significantly more frequently and laid more eggs than the moths in the other cages, says Xiao.

To understand why that happens, the scientists analysed the antennae of male moths that they had raised in conditions with 15 hours of normal light and 9 hours of dim red light. They found that these moths had more odorant binding proteins (OBPs) in the smell receptors of their antenna neurons, apparently making them hypersensitive to female sex pheromone odours.

It’s possible that this occurs because red light has a long wavelength that can pass through animal tissue and stimulate cellular activity, the researchers speculate.

Such findings no longer surprise Xiao, he says, because insects are full of surprises. “There are too many things unknown in nature, especially in the insect world.”

Journal reference: Frontiers in Genetics, DOI: 10.3389/fgene.2021.611476/full