Ethological evidence for sexually exploitative pollinator attraction by Arisaema serratum (Araceae).

Deceptive pollination exploits pollinator perceptual biases while offering no reward. Arisaema (Araceae) employs an extreme form of this strategy, in which fungus gnats are lured into a slippery floral tube that often proves fatal. However, the key factors governing attraction and capture remain poorly understood, partly due to the typically low frequency of floral visitation. Preliminary observations revealed that Arisaema serratum exhibits a relatively high visitation rate of fungus gnats. We therefore conducted direct behavioral observations of pollinators associated with A. serratum in a controlled field plot, combining video monitoring with morphometric analyses. Over two years, we recorded 2459 visits by male Cordyla sixi (Mycetophilidae) during 64 hours of observation, confirming a highly specialized interaction. Visit frequency declined only after floral senescence, with no progressive decrease observed within daily sessions, indicating negligible learning-based avoidance. Morphometric analyses suggested a positive correlation between thicker appendices and increased visitation, as well as between larger spathes and increased visitation, but a negative correlation between higher inflorescence placement and visitation, likely reflecting the low flight path of fungus gnats. Behavioral observations revealed frequent genital displays, wing-fanning, and exploratory walking on the appendix. Simultaneous visits by multiple males prolonged residence time and facilitated the arrival of additional individuals. Together, these findings support a scenario in which floral scent mimics sexual or aggregation pheromones, attracting dense male assemblies and enhancing pollination success. This study provides the first detailed ethogram of fungus gnat behavior associated with Arisaema, thereby offering novel insights into the mechanistic basis of this highly exploitative pollination system.