The red light cheered up the moths

PICTURE: Female yellow peach moth Conogethes punctiferalis view more

Credit: Wei Xiao / Southwest University, China

Do you dim the lights and turn on the red light for a romantic night out with a partner? It turned out that moths do not differ that much in that respect. A new study published in Boundaries in genetics shows that dim red light enhances sexual activity in model, yellow peach moth Conogethes punctiferalis (family Crambidae), by selectively activating the genetic pathway associated with the sense of smell in antennae. This time ultimately makes men more sensitive to the smell of the female sex pheromone and thus more motivated to mate.

“We usually use red lights when we work with moths because long-lasting white light can prevent them from mating,” says lead author Dr. Wei Xiao, a scientist from Southwestern University in Chongqing, China. “However, we realized that moths laid more eggs when we shone red light during the dark phase of their daily light-dark cycle, and we wanted to determine the molecular mechanisms underlying this change.”

Odorant binding proteins (OBPs) are small proteins secreted by helper cells that surround odor receptor neurons in insect antennae. Xiao and colleagues first used quantitative PCR (qRT-PCR) to show that two OBPs, encoded by the CpunOB2 and CpunPBP5 genes, are more abundant in male antennae C. punctiferalis exposed to red light of medium intensity (about 2 lux) than in antennas exposed to darkness or light of other wavelengths. The authors hypothesize that the relatively long wavelength of red light allows entry into tissues and cells and stimulates the expression of CpunOB2 and CpunPBP5 by a still undetermined mechanism.

Xioa et al. he then used another molecular technique, the fluorescence binding assay, to show that these OBPs, when recombinantly expressed in E. coli bacteria, selectively bind to molecules known to be components of the female sex pheromone moth. Electroantenography, a technique that measures electrical activity in antennae in response to stimuli, has shown that male antennae become more reactive to the female sex pheromone after exposure to red light. Finally, they used behavioral experiments to confirm that the ultimate effect of red light on men and women C. punctiferalis is to stimulate mating and egg laying.

Xiao et al. conclude that at least for this species the dimmed red light is sufficient to make the olfactory receptor neurons in the antennae of males hypersensitive to the components of the female sex pheromone, which ultimately enhances the reproductive behavior of adult moths.

Although the yellow peach moth itself is not endangered, Xiao’s study could potentially help promote reproduction in at-risk species or species that are economically important.

“Our study is the first to test the stimulatory effects of red light on mating behavior and is therefore a potential springboard for exploring new conservation techniques for endangered insects,” Xiao says.

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