Most species of the plant genus Arisaema exhibit a striking sexual dimorphism in spathe morphology: the male inflorescence has a basal exit for visiting fungus gnats (Diptera) to escape after pollen transfer, whereas the female inflorescence acts as "lethal kettle trap", fatally entrapping visiting fungus gnats. This seemingly antagonistic system has long puzzled researchers - how could such a relationship persists evolutionarily if pollinators are killed?

Researchers from the Reproductive Ecology Group at the Wuhan Botanical Garden, Chinese Academy of Sciences have uncovered the hidden mutualism that may explain this paradox.  

Through extensive field observations and laboratory analyses of Arisaema bockii in a subtropic forest habitat in China, they find that fungus gnats lay eggs inside the female spathes of Arisaema species. The team documented the full life cycle of fungus gnats - from egg, larva, and pupa to adult - all developing within these inflorescences, which act as both oviposition sites and nurseries. 

However, since no food reward is provided by the plant, the larval food source remained a mystery. Through close observation, the researchers discover that the decaying bodies of adult fungus gnats, fatally trapped in the kettle trap, serve as a key nutritional resource for larval development. 

This suggests a hidden mutualism: Arisaema provides brood sites for fungus gnat offspring, while the larvae scavenge on their conspecific corpses to survive. This mechanism may contribute to the long-term maintenance of this unique pollination system.

The study, titled "Scavenging contributes to larval food intake in fungus gnats using the Arisaema kettle trap as a brood site", has been published in the journal Ecology.  HUANG Wen and LI Xin are co-first authors, Prof. YANG Chunfeng is the corresponding author, and Prof. WANG Qingfeng and Prof. Jon Ågren (Uppsala University, Sweden) provided key guidance. A photo gallery of the findings was also published in The Bulletin of the Ecological Society of America. The work was supported by the National Natural Science Foundation of China and the CAS Strategic Priority Research Program.

Inflorescence of Arisaema bockii and the fungus gnat larvae feeding on adult corpses. (A) A. bockii in the natural habitat. (B) Male inflorescence of A. bockii; the orange arrow indicates the basal exit hole through which fungus gnats escape after visiting. (C) Female inflorescence of A. bockii, which lacks an exit hole and traps fungus gnats, serving as an oviposition site. (D) Fungus gnat larvae feed on decaying adult carcasses. (Photo credit by HUANG Wen)