Rhyssomatus nigerrimus, often known as the soybean weevil, is a significant pest in soybeans in Mexico and only reproduces on soybeans. Weevils aren’t generally known for being noisy, but some do indeed chirp like some of their insect cousins. A new study examines the acoustic signals of soybean weevils to shed light on how they signal each other for mating or emitting distress calls. (Photo by echame via iNaturalist, CC BY-NC 4.0)

By Grant Bolton, Ph.D.

Grant Bolton, Ph.D.

Summer days and evenings can bring out a symphony of insect noises. The usual suspects are the consistent chirping of field crickets, the raucous screeches of cicadas, or perhaps the stridulations of a katydid.

They’ve all got the same thing on their mind. Attracting a mate and keeping all the competition away.

But what about the insects you don’t typically associate with audible communication? Beetles, especially weevils, aren’t known for being noisy. And yet, with more than 50,000 species worldwide, at least a few were bound to break the silence.

Recently, researchers at the Sierra Nevada Research Institute and Mexico’s National Institute for Forestry, Agriculture, and Livestock Research tuned into a weevil pest of soybeans, and they discovered it was far from quiet.

Soybean Weevils

Rhyssomatus nigerrimus, often known as the soybean weevil, is a significant pest in soybeans in Mexico and only reproduces on soybeans. These weevils congregate in soybean fields, where adults feed on leaves and pods and females lay their eggs inside developing seeds. The larvae grow within the beans themselves, reducing yield and seed quality.

Adding to the challenge, soybean weevils aren’t acting alone. Adults gather in conspicuous groups on soybean plants, forming dense mating clusters. For farmers, these aggregations spell trouble. But, for scientists, they offer an opportunity to answer a key question: If weevils were clustering to mate, how exactly do they signal to one another?

Measuring the Sound of Silence

In a study published in July in the Journal of Economic Entomology, a research team led by Andrea Joyce, Ph.D., at the University of California, Merced’s Sierra Nevada Research Institute recorded both male and female soybean weevils as they aggregated on soybean leaves. Soybean weevils produced faint chirps in two distinct patterns. The first was a pattern of paired chirps, and the second was a series of chirps.

The weevils made the sounds by rubbing their hardened forewings (elytra) against their abdomen to create a squeak. Why both males and females “chirp” remains an open question. The leading hypothesis is species recognition, allowing the beetles to identify one another in crowded leaf clusters.

Interestingly, the longer sequences may act as a distress call, the researchers say. The series of chirps was more likely to be produced when males were in larger groups of five or 10 on a leaf. Females didn’t produce the noise as often in large groups.

These findings suggest that even insects that were once thought to be silent may be producing acoustic signals for mating and intraspecies communication. For a crop pest like soybean weevils, decoding those messages may be beneficial to farmers. If researchers can decode when and why weevils “speak,” it may open new possibilities for monitoring populations or even disrupting their conversations to limit damage in soybean fields.

More broadly, the discovery of chirping soybean weevils adds another layer to the rich story of insect communication. While some insects announce themselves loudly, others rely on faint signals detectable only with careful study. For scientists, this finding highlights how much remains hidden in the insect world, even among familiar agricultural pests.

Ultimately, one thing is clear: in the insect world, silence is rarely what it seems.

Grant Bolton, Ph.D., is a freelance writer and voice actor with a Ph.D. in entomology based in western Missouri. Email: [email protected].