**Summary: Japanese Researchers Discover Fungal Nurseries in Female Dinidoridae Stinkbugs that Protect Eggs from Parasitic Wasps**
For decades, scientists believed that female stinkbugs of the Dinidoridae family, a small group of insects native to Asia, possessed tympanal organs—a kind of hearing structure similar to eardrums—on their hind legs. These organs were assumed to help the bugs detect sounds, perhaps even the courtship songs of males. However, new research led by Takema Fukatsu, an evolutionary biologist at the National Institute of Advanced Industrial Science and Technology in Tokyo, has turned this assumption on its head.
Upon taking a closer look at the hind leg structures of Megymenum gracilicorne, a Dinidoridae species found in Japan, Fukatsu and his team discovered that these so-called tympanal organs were not actually hearing organs at all. Instead, they found something far more unusual: these structures serve as mobile fungal nurseries, a phenomenon previously undocumented in this form among insects.
**A Closer Look Reveals Fungal Gardens, Not Ears**
Most insect tympanal organs are found on the front legs or on the abdomen. The presence of these organs on the hind legs of Dinidoridae females was already unusual, prompting Fukatsu’s team to investigate further. Their initial objective was to understand how this odd placement might influence the stinkbugs’ ability to hear.
However, their investigation quickly revealed that the hind leg structures lacked the essential components of hearing organs, such as a tympanal membrane and sensory neurons. Instead, the researchers found thousands of tiny pores filled with filamentous fungi. These pores were connected to secretory cells that appeared to provide nutrients, allowing the fungi to thrive. In adult females, the structure was even visibly coated with white fungal hyphae.
**How Fungal Nurseries Work in Stinkbugs**
The existence of insect-fungal partnerships is not entirely new. For example, Ambrosia beetles are known to have special organs for transporting and cultivating fungi, which serve as food for their larvae. Yet, in the case of Dinidoridae stinkbugs, the function of the fungal nursery is entirely different. Instead of food, these stinkbugs use the fungi to coat their eggs with a protective fungal blanket.
To observe this process, Fukatsu and his colleagues watched Megymenum gracilicorne females both in laboratory settings and in the wild. The females lay their eggs in a row, then scrape the fungal nursery on one leg with the claw of the other leg to gather fungal spores. They then smear these spores over each egg. Within three days, the eggs are enveloped in a thick, white fungal layer, roughly two millimeters deep.
**Protection Against Parasitic Wasps**
The purpose of this fungal coating soon became clear. Parasitic wasps, which often lay their eggs inside stinkbug eggs, were unable to penetrate the fungal blanket. Experimental tests showed dramatic results: