• Mesler, Michael R.

Fungus gnats (Sciaridae and Mycetophilidae) are the principal pollinators of Listera cordata (L.) R. Br. (Orchidaceae) and Scoliopus bigelovii Torr. (Liliaceae) in coastal redwood forests of northern California. Although primitive diptera have generally been regarded as relatively inefficient pollinators, fruit set for both species is high: 61-78% for L. cordata (1976-1978) and 94.3%-98.5% for i (1978-1979). Since probability of pollination per visit is low, we attribute high fruit set to the large number of gnats present at our study sites and corresponding large number of visits to flowers. The relative frequency of geitonogamous vs. xenogamous pollen flow was estimated by emasculating flowers and subsequently comparing pollen reception or fruit set of emasculates with controls. Results for both species indicate that interplant movement of pollen is common. Thus, fungus gnats can be effective pollen vectors, both in terms of overall fruit set and potential for cross-pollination.