Indian biologists have studied crickets, whose males arrange "amplifiers" from the leaves: this makes their chirping twice as loud and completely irresistible to females.
By quickly rubbing the elytra against each other, male crickets emit a characteristic chirping, signaling their presence to competitors and potential mating partners. The louder the sound, the more formidable rival it seems to males and the more attractive it is to females. All this stimulated a real evolutionary race for loudness, in which the tree crickets Oecanthus henryi used a trick, quite unexpected for such "primitive" animals: they learned to amplify the sound of their chirping.
As you know, some bumblebees bite off pieces of leaves to speed up the flowering of plants. And some male O. henryi crickets gnaw out a hole in the center of the leaf of such a size that they would hold in it, slightly getting stuck, and chirp from this unusual position. This "natural megaphone" allows them to more than double the volume. The unexpected behavior of insects is highlighted in a new article published in the journal Proceedings of the Royal Society B.
The authors of the work - scientists from the National Center for Biological Sciences in Bangalore, India - note that the ability of crickets to use reflective acoustic screens to amplify sound was known before. They are not the result of learning: the mechanism is innate and is equally manifested by insects that have grown both in an artificial and in a natural environment. However, this time the researchers decided to understand this behavior in more detail.
Observing in the field, they showed that only about five percent of O. henryi males arrange for themselves “megaphones” made of leaves (25 out of 463 tracked individuals). On average, they are smaller than the rest and chirp quieter, however, due to the reflective surface of the sheet, the volume is more than doubled.
This sound is produced by crickets in much the same way as violins and cellos - due to the vibrations created by the friction of one elytron against another, serrated, which resonates and creates a chirp. Having settled in the opening of the leaf and pressing their wings against it, the insects increase the size and increase the power of the resonator, and with them the volume. Likewise, we sometimes strengthen our voice by placing our palms with a funnel over our mouth.
To make sure that these screams really work, the authors of the study set up experiments in the laboratory. They demonstrated that O. henryi females showed an interest in louder chirping, whether it was the result of the male's larger size or his use of a resonator leaf. In this way, behavioral cunning evens out the chances of large and small males to reproduce.
A curious feature of the mating of crickets is the duration of this process: the female can control the amount of sperm that she receives from a particular male, due to the duration of copulation. Mating with large males can take more than half an hour, with small males it lasts several times less, allowing you to transfer a smaller number of spermatozoa. However, the loudness of the crickets used by the resonators changed this behavior as well. With such "small, but noisy" males, mating lasted as long as with large ones. Why the female is so "deceived" is not yet known.