Fly pollination in <i>Impatiens orchioides</i> Bedd. (Balsaminaceae): Possible role of fungus gnats and phorid flies as pollinators

Abstract The pollination biology of Impatiens orchioides Bedd., a rare, endemic, scapigerous, and critically endangered balsam species, was surveyed by assessing the populations distributed across four different areas in the Nilgiri district of the Western Ghats. Impatiens orchioides usually blooms during the peak of southwest monsoon, that is, between mid‐July and the last week of September. Flowers are few on the scape inflorescence, hermaphroditic, and zygomorphic, with pale reddish‐brown lateral and middle petals and an ovary‐anther complex at the center. A shallow nectariferous pit containing a thin film of nectar was observed. The pollen–ovule (P/O) ratio was 191:1. Impatiens orchioides showed a 65.7% fruit set and 74% seed set under natural conditions. Flies were the major visitors of I. orchioides . Bradysia sp. (Sciaridae), Exechia sp. (Mycetophilidae), and unidentified flies from the Phoridae and Drosophilidae families were observed visiting the flowers at very low frequencies. Based on the compatibility of insect size, space available between the nectariferous pit and anther‐ovary complex, as well as the pollen load and frequent contact, phorid flies and Bradysia sp. are likely to contribute significantly to the pollination of I. orchioides more than Exechia sp. The nectar analysis revealed the presence of fructose (21 mg/mL), glucose (0.76 mg/mL), and sucrose (0.11 mg/mL), which serve as a major floral reward for these insects. However, this species faces several challenges, including a limited population size, a narrow distribution range, a low number of pollinators, and habitat threats. Therefore, it is essential to prioritize the conservation of this unique balsam species.