Stinkbug Leg Organ Hosts Symbiotic Fungi That Protect Eggs from Parasitic Wasps

Summary

In an astonishing discovery that redefines our understanding of insect anatomy and symbiosis, researchers have uncovered a unique fungal nursery hidden within the hindlegs of female dinidorid stinkbugs, challenging the long-held assumption that these structures served as auditory organs. Traditionally, the conspicuously enlarged surface on the hindleg of female dinidorid stinkbugs has been identified as a tympanal organ—an evolutionary adaptation seen in various insect species for detecting sound. However, pioneering investigations into the Japanese species Megymenum gracilicorne reveal this organ is instead a sophisticated fungal symbiotic hub, instrumental in safeguarding the next generation against parasitic threats. Detailed morphological analyses showed that what was presumed to be a thin, sensitive tympanal membrane is, in fact, a robust cuticular surface densely perforated by thousands of tiny pores. These microscopic openings are conduits for glandular secretions, which nurture the growth of symbiotic fungal hyphae directly on the insect’s leg. This fungal symbiosis is far from a passive association; it represents an active, evolved mechanism whereby female stinkbugs coat their freshly laid eggs with a living fungal shield.The ecological implications of this discovery are profound. Parasitic wasps are notorious for exploiting stinkbug eggs, depositing their own larvae inside and effectively hijacking the stinkbug’s reproductive success. However, the fungal hyphae emanating from the leg organ form a physical barrier that deters such parasitism. Behavioral observations and controlled experiments demonstrated that when eggs are fully smeared with fungal filaments, parasitic wasps are unable to oviposit successfully. In contrast, eggs that were stripped of these fungal coverings—or those laid by females with surgically removed hindlegs—experienced dramatically elevated rates of parasitism. Molecular identification of the fungal constituents uncovered a diverse a...