How Insects’ Songs of Love May Be Used Against Them

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Hoppers having a shmooze, March 2018.
Hoppers having a shmooze, March 2018.Credit: Migal Galilee Research Institute

The caged hoppers in the Hula Valley lab live the life of Riley. The temperature in their room is controlled for their comfort. Nobody shoos them off the succulent leaves growing there; they can gnaw them as they please.

But these little guys are blithely unaware they’re being closely observed for information that will lead to the most efficient, least environmentally damaging way to keep their numbers down.

Spraying crops with poisons that kill bugs doesn’t do favors to other life forms either. Moreover, insects develop resistance. This kind of pest control has severe limitations. Now scientists believe the key to the process may lie in confusing the insects. How? By singing them their own song.

Or as the scientists call it, harnessing biotremology, the study of how acoustic vibrations affect animal behavior.

As crop pests go, the leaf and plant hoppers that Dr. Rakefet Sharon studies (among other agricultural pests) aren’t the worst. These are no locusts that devour everything green in their path.

But hoppers can inhibit a plant’s growth. Grapes, whether grown for food or wine, suffer from these wee beasties, as do pomegranate and almond trees, Sharon says. And since farmers began cutting back on classic extermination techniques, the hoppers’ numbers have grown.

In temperate Israel, hoppers live more or less year-round, with a three-week breeding cycle in the summer, six-week cycles in the spring and autumn and a two-month cycle in the winter.

Climate change and global warming have clearly made the problem worse, Sharon says. When winters are warmer, as this last one has been, temperatures remain above the insects’ development threshold (15 degrees Celsius) over a significant stretch.

“Since we aren’t dealing with insects that hibernate, but only slow down, we have a greater number of generations and their date of appearance is earlier,” Sharon told Haaretz.

Of course, to thrive, the bugs’ relevant host plants also need to develop. But if one of the crops they like to eat “wakes up” early, and they do too, the restaurant is open.

Credit: Valerio Mazzoni, Fondazione Edmund Mach, Italy

No killing them all

The goal isn’t to exterminate plant and leaf hoppers entirely. Nature abhors a vacuum. Eradicate one pest and it will just be replaced by another, says Sharon, an eco-entomologist studying the issue at Northern R&D, a center for agriculture-related research and development in Israel’s north. It works with the Migal life sciences institute in Kiryat Shmona.

Why use hoppers, anyway, rather than directly target an insect that does worse damage to crops? They’re a great model, Sharon explains, not least because they can be bred in the lab, which isn’t the case for all insects. Also, Israel has dozens of species of hoppers, and it’s useful to see what happens when multiple species interact.

Insects communicate in various ways, including by emitting the chemicals known as pheromones. Around 92 percent of insects use audible communication, but most use frequencies the human ear can’t hear.

Grasshoppers and cicadas, for instance, rub a hind leg against one of their hard forewings, causing the wing to vibrate, not unlike a violin bow and strings.

Leaf and plant hoppers drum. In fact, these hoppers have a range of drumming sounds, achieved by tapping on leaves – each species specific. One hopper species won’t understand the language of another.

A hopper has one sound for wooing, another as a territorial protection device and even a war song. Sharon is studying the hoppers’ communication with Ally Harari of the Volcani Center near Tel Aviv and Valerio Mazzoni of the Italy-based Edmund Mach Foundation, who can now distinguish between one hopper and another.

What are the hoppers saying? I’m here. I’m gorgeous, if it’s a male talking to a female. Or I’m here and this is my territory, hop off, if it’s a male talking to a male. In some species both sexes generate sounds, in some species only the males.

Friendly noise pollution

So if you tape a male hopper threatening other males and play it in the field, the other males will feel discouraged. Or farmers can play the song of a female laying eggs so other females go elsewhere to lay.

Which begs the question of why the disgruntled hoppers wouldn’t just go to Yossi’s field next door. They would of course unless Yossi also plays the bugger-off hopper sounds.

Like the case of pheromone-based pest control, all planters in the area have to use it for it to be effective. The same will apply to population reduction through confusion, Sharon says. Any potential noise pollution once the technology is developed will pale compared to the damage wreaked by other forms of pest control.

Meanwhile, population reduction by way of playing hoppers back their own songs is a distant goal for the Israeli team, which is focusing at this stage on monitoring, says Sharon. Right now the only way to detect and evaluate a hopper infestation, to judge if it’s extermination-worthy or should be left alone, is to see and count the bugs, which requires lots of funding and staffing. “We aim to give farmers a tool,” Sharon says.

The specific sounds the hoppers generate are recorded using laser technology that senses the vibration of the leaves on which the insects are playing their songs. Mazzoni has learned to distinguish among the songs of rival males.

The lasers “reading” the leaf vibration in northern Israel are handled by Prof. Yizhar Lavner of Tel Hai Academic College’s Computer Science Department. The signal is taped, sampled and analyzed for structure, rate and composition. The next stage will be to correlate characteristics of the insect's signal and behavior, or physiology. The goal is an automated system that can distinguish between insect species, say how many are there, and tell what they’re doing, whether courting, mating, fighting, eating and so on.

But don’t hold your breath for biotremology as an ecologically friendly pest-control device in Israel. Sharon estimates that it could take around 15 years to develop. Meanwhile, for around two years now, since a biotremology conference in Italy, scientists around the world have been collaborating on building a library of insect-generated songs. Wait for it: drones with receivers for the hoppers’ acoustic signals.

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