Japan – Video and observations of the Japanese dinidorid stinkbug Megumenum gracilicorne reveal that the female’s hindlegs, previously thought to be “ears,” are actually specialized symbiotic organs.

Researchers discovered that these organs harbor filamentous fungi allied with Cordyceps. During egg-laying, the female transfers the fungi from her hindlegs onto her eggs. The resulting hyphal coating physically blocks parasitic wasps, protecting the eggs from predation.

Laboratory and field experiments confirmed the protective effect: eggs covered in the fungal hyphae consistently showed lower rates of parasitism compared to eggs without the coating.

Further studies across diverse dinidorid stinkbug species from Taiwan and southwestern Japan showed that all examined females possess similar hindleg organs and exhibit the egg-smearing behavior. Scientists conclude that this organ and behavior likely evolved in a common ancestor of the Dinidoridae family.

This discovery overturns decades of assumptions that the female-specific hindleg organ served as a tympanal ear. Instead, it demonstrates a remarkable evolutionary adaptation for microbial symbiosis, integrating morphological, cellular, and behavioral traits to defend the next generation.

Podcast: Play in new window | Download