Some stinkbugs’ legs carry a mobile fungal garden

What Fukatsu discovered was a mobile, self-sustaining fungal garden. “In adult female, this organ was covered with white fungal hyphae,” Fukatsu said. So far, a functionally similar feature has been found in insects like Ambrosia Beetles, which have pocket-like organs used to transport and release fungal spores into holes bored in wood. This way, the beetles create fungal gardens that their larvae and adults can feed on. But in Dinidoridae, the purpose of mobile fungal nurseries is entirely different. The stinkbugs use the fungi to cover their eggs with fungal blankets. Keeping wasps at bay To find out how Megymenum gracilicorne females use their fungal nurseries, Fukatsu and his colleagues observed the bugs in both the lab and in the wild. “They lay eggs in a row and they smear the fungal spores on each egg,” Fukatsu explained. During oviposition, the females scratched their fungal nurseries with a claw on the other leg and then rubbed the eggs. Within three days, the eggs were almost entirely covered with a roughly two-millimeter-thick layer of fungi. The purpose of these fungal blankets was to protect the eggs from parasitic wasps. “When the eggs were covered, the wasps could not approach them—pierce through them to lay their own eggs in the Dinidoridae stinkbug eggs,” Fukatsu said. The team performed a series of experiments that involved releasing the wasps in a container with stinkbug eggs fully covered with fungi and eggs where the fungal blanket was artificially scraped off. It turned out that the blankets significantly reduced the wasp parasitism. The wasps managed to parasitize 62 percent of the fungi-free eggs. In eggs covered with the fungal blankets, this rate was down to 10 percent. Surprisingly, the fungi did not infect the wasps or cause them any harm; the blankets worked more like a physical barrier than a chemical deterrent. “Even when we kept the wasps in Petri dishes full of spores for a full day, they were very happy—they never died,” Fukatsu explains.