Scientists Find the First Evidence of Insects Choosing Egg-Laying Site Based on Plants’ Sounds

When giving birth, a women pay crucial attention to physical safety and nutrition. Moth females are no different. For them, however, the birthing space is not a house or a healthcare facility. It’s a plant. When choosing a plant to lay their eggs, these females perform a special analysis of the various plant options to decide which would be the safest and the most nutritious one to feed their larvae. In a new study published in the journal eLife Sciences, researchers revealed that they use “plant sounds” to make this decision, the most important decision of a moth mom’s life.

Mysterious communication

Most insects rely on the visual, chemical, tactile, and electrical cues given by plants to determine whether they are safe and healthy. One such cue is ultrasonic sounds. Researchers mentioned in the study that plants emit these ultrasonic signals when triggered by some physiological processes such as cavitation, dehydration, or cutting. Meanwhile, insects have tiny sensors embedded on their bodies that help them detect these signals, which are otherwise inaudible to human ears. These sensors in insects serve two main functions: attracting each other for mating by detecting sounds, and defending from predators.

First-ever plant-insect interaction

Two years ago, researchers from Tel Aviv University (TAU) discovered that plants tend to scream when they are in distress, according to a study published in Cell. In the latest study, the same team of researchers experimented on female Egyptian cotton leafworm (Spodoptera littoralis) moths to reveal that they use these ultrasonic sounds to decide whether or not to lay their eggs on a certain plant. “In this study, we revealed the first evidence for acoustic interaction between a plant and an insect,” researchers said, according to the press release.

How female moths choose a plant to lay eggs?

Female moths are known to lay their eggs on tomato plants. While they feed themselves on flower nectar, the larvae that hatch on the plants feed on the nutrients. So while they select a plant for laying eggs, they ensure that the plant is healthy and not dehydrated. “After proving in the previous study that plants produce sounds, we hypothesized that animals capable of hearing these high-frequency sounds may respond to them and make decisions accordingly,” study author Professor Yossi Yovel from TAU said in the press release. He and his team found that when plants emit distress signals or clicking sounds of dehydration, moths choose to fly away and select another plant for oviposition.

Three experiments

The team repeated each experiment at least nine times with a different crew of females. Three different combos were used for investigating the motivation behind moths’ decisions. In the first experiment, an eclipse of moths was presented with two boxes: one with the playback recording of a tomato plant, and the other box played no sound at all. In this case, the moths chose the box that produced the sound. In the second episode, both the boxes presented to them were silent. Moths chose both boxes equally. This indicated that their decision-making was based on their “hearing plant sounds.”

In the following part of the experiment, the female moths were presented with two boxes: one with the recording of a dehydrated tomato plant, and the other was silent. In this case, the insects chose the silent box, as the dehydrated plant emitted signals of distress. In the last episode, one box contained nothing, and the other was filled with male moths. Since male moths also emit ultrasonic sounds, the researchers wanted to test whether it is just the plants or the hearing that the females were relying on for their decision.

In this case, females laid eggs equally in both boxes. This indicated that the primary motivation behind their decision was “hearing.” They chose to lay eggs upon signals of silence and healthy noise, but when bombarded by sounds of distress, they chose to fly away. Researchers believe that this experiment is just the beginning. They have just started exploring the mystery of plant-insect communication, and there are vaster, greater worlds waiting to be explored.

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