Why Genetically Modified Flies Don’t Want Sex

By Kate Horowitz

Birds do it. Bees do it. But genetically modified fruit flies just aren’t in the mood.

In what could be called the chemical equivalent of a cold shower, an international team of entomologists has discovered how to decrease some pest insects’ interest in sex. (Related: “Female Flies Put Up a Fight to Keep Sex Short.”)

fruit fly picture
A fruit fly. Photograph by Solvin Zankl/Visuals Unlimited/Corbis

The team, led by Kansas State University’s Yoonseong Park, reveals in a new paper that the secret to killing some bugs’ buzzes is to shut off a specific chemical in their brains. Park and his colleagues recently discovered the chemical—a neuropeptide called natalisin—while studying the genomes of fruit flies and red flour beetles.

Neuropeptides are molecules that carry information from one neuron to the next. An animal brain contains dozens of them, each with its own function, from eating and metabolizing to learning, remembering, and reproducing. When the researchers turned off the natalisin—which they named for the Latin word natalis (“birth”)—in their subjects, they turned off some of their subjects too.

Lowering Sex Drive

The team used a process called RNA interference, or RNAi, to silence natalisin in the insects’ genes. Red flour beetles with suppressed natalisin copulated as usual, but laid 50 to 75 percent fewer eggs than the beetles with unsuppressed natalisin. Nor did it matter which parent had been treated; if either the father or mother beetle had silenced natalisin, the egg count was lower than average. (See “Some Females Too Sexy for Own Good, Fly Study Says.”)

The fruit flies’ reaction was even more extreme. Natalisin-suppressed males showed what the paper—published in the August 26 issue of Proceedings of the National Academy of Sciences—described as “moderate but significant levels of delay in initiating courtship.”

Suppressed females “displayed significantly elevated levels of grooming, which likely prevented the males from being able to access the females for attempted copulation.”

Without natalisin, in other words, the fruit flies just didn’t feel like doing it. All told, only about 10 percent of the natalisin-suppressed flies wound up mating. Those with intact natalisin went about their business, getting busy as usual.

Curiosity aside, one might wonder why scientists would interfere with the sex lives of tiny insects. The answer is that their research has bigger-picture implications. In this case, Park said he hopes the team’s findings will lead to environmentally friendly pest control.

“Natalisin is unique to insects and [other] arthropods and has evolved with them,” he said. That means that turning it off could offer a widespread form of crop protection that wouldn’t affect the plants or other animals.

Promising Field

The field of genetic pest control is a promising one. Selecting which genes or chemicals to knock out “can be highly specific to an insect,” says entomologist Wayne Hunter of the U.S. Department of Agriculture’s Agricultural Research Service.

Unlike most pesticides currently in use, neuropeptide suppression could “target one insect feeding on a tree and not hurt other insects, or not hurt beneficial insects, like predators that eat the insect you have targeted.” (See “Why Female Flies Eat Sperm.”)

Microbiologist John Burand of the University of Massachusetts, Amherst, agrees. Identifying targets like natalisin, he says, is “key to the success and the specificity of this approach.”

The natalisin team comprises researchers from the United States, Slovakia, and South Korea.

Next steps include finding out exactly how the neuropeptide works, what it does in other insects, and how best to turn chemically induced chastity into practical pest control.