Back from the dead: A fungus gnat pollinator turns Arisaema lethal trap into nursery

Abstract

Societal Impact Statement The research explores the complex interaction between flowering plants and their pollinators, specifically focusing on the genus Arisaema. Unlike most plants, Arisaema has a distinctive trait in which killing pollinators can be beneficial. Traditionally, this interaction has been viewed as highly antagonistic because it appears to favor the plants at the expense of the pollinators. However, new evidence reveals that a pollinator uses the lethal floral trap of Arisaema thunbergii as a nursery. Remarkably, some individuals probably even escape from the trap after laying eggs. This finding challenges the prevailing notion that deceptive pollination is the sole outcome in Arisaema, a genus known for its intricate lethal pollination mechanisms. Summary While many flowering plants engage in mutualistic relationships with their pollinators, flower‐insect interactions are not always mutually beneficial. Some plants exploit their pollinators by deceptively promising rewards without delivering them. Among such plants, the genus Arisaema (Araceae) is notable for its antagonistic behavior towards pollinators, as female plants invariably entrap them with lethal effects. Here we tested the hypothesis that the succulent appendix of some Arisaema species, such as Arisaema thunbergii, may serve as a food source for pollinator larvae, leading to the possibility of nursery pollination. To investigate this, we retrieved adult insect corpses trapped within the spathes of A. thunbergii. Subsequently, we incubated the spathes after collecting the corpses to determine if conspecific insects emerged from them. We present novel evidence that one of the main pollinating fungus gnats, Leia ishitanii, uses the lethal floral trap of A. thunbergii inflorescences as a nursery. Astonishingly, some L. ishitanii individuals may even succeed in escaping from the female spathe after depositing their eggs. These findings challenge the conventional understanding that deceptive pollination is the norm within the genus Arisaema. The interaction between A. thunbergii and L. ishitanii, in which a significant portion of female adults die inside but still reproduction seems successful, suggests an intermediate stage between brood‐site deception and nursery pollination mutualism.

Keywords

• brood pollination
• deceptive pollination
• lethal kettle trap
• mutualism–parasitism continuum
• nursery pollination
• trap flower