When it comes to the sex lives of insects, entomologists sure know how to kill the mood. To keep pests from making love—and little bugs—they have developed all sorts of tricks, like spraying plumes of pheromones that lead love-struck males astray. Now, scientists have developed a new way to disrupt mating: shaking the insects’ perches to disrupt the vibrations that would-be partners normally use to find each other.
“This is a great new approach,” says Christoph Hoffmann, a biologist at the Institute for Plant Protection in Fruit Crops and Viticulture in Siebeldingen, Germany. These good—or bad—vibrations not only stop reproduction, but they may prevent a species of leafhopper from spreading a deadly disease through Europe’s vineyards.
After the American grapevine leafhopper (Scaphoideus titanus) was accidentally imported into Europe in the mid-19th century, likely with plant material brought to combat the Great French Wine Blight, the insects picked up a bacterium that causes a grapevine disease called flavescence dorée, which causes leaves to yellow and grapes to shrivel. Since then, the leafhopper has been slowly spreading the incurable disease throughout the wine-growing regions in southern Europe.
To combat the pest, entomologist Valerio Mazzoni and colleagues at the Edmund Mach Foundation, an agricultural institute in Trentino, Italy, decided to use the leafhopper’s mating signals against them. Leafhopper males “sing” with their legs, vibrating the leaf on which they sit and alerting any nearby females. A female answers with her own vibration, starting a duet that helps the male locate her.
To disrupt the performance, the team played a continuous stream of male singing from laboratory loudspeakers, causing a grapevine cutting with two leaves to shake. The upper leaf hosted one male, and the lower leaf one female. In almost two dozen experiments, not a single male could find the female when the song was played at a high enough volume. In an outdoor experiment, the team hung electromagnetic “shakers” on the supporting wire of a row of grapevines and put pairs of insects into cages wrapped around the shoots. After a day, they checked to see whether the caged insects had mated. In cages 5 meters from the shaker, 33 out of 36 females had not yet mated. That number dropped with increasing distance from the shaker—at 35 meters, only six out of 17 females had not mated—as the authors write in this month’s issue of the Journal of Pest Science.
Hoffman welcomes the new approach to leafhopper control. Because the insects do not use pheromones for attraction, classic mating disruption is not an option. So vintners in many regions are forced to spray insecticides several times a year, Hoffmann says. “Any new approach is welcome, and I think the data here allow us to conclude that this is possible in principle.” The biggest questions for now may be practical. For instance, how do you hang electric cables in vineyards that harvest using machines with rotating knives?
And, of course, there is always the question of cost. The researchers don’t give a final cost per hectare, but their proposed equipment price of 300 euros per hectare “would be great,” Hoffmann says. The team says it should be possible to reduce the price of the equipment and lower costs by turning off the shakers for the 8 hours each day that the hoppers are inactive. Indeed, several companies have shown an interest since the paper came out, Mazzoni says.
“The idea is ingenious,” says Hannelore Hoch, a biologist studying planthoppers at the Leibniz Institute for Evolution and Biodiversity Science in Berlin. Unlike insecticides, the mechanical disruption is targeted specifically at the pest insects. And because no other insects transmit the bacterium, getting rid of the leafhoppers would be enough to protect the vineyards—for now. But she cautions that the leafhoppers might adapt and start mating on other plants. And she wonders how the vibration might affect the vines in the long run. They might grow stronger, for instance, and produce lower yields in the process, Hoch says. “When you intervene in a biological system you never know exactly what will happen.”