Pollination and insect visitors to the putatively brood-site deceptive endemic spurred helmet orchid, Corybas cheesemanii

Abstract

Deceptive orchids typically employ food or sexual deception of male insects. Brood-site deception, when flowers are pollinated by female flies fooled into attempting oviposition, is less well characterized for orchids but is probably common among New Zealand terrestrial orchid species. Helmet orchids (Corybas, Nematoceras and related genera) are considered specialist brood-site deceivers that mimic mushrooms and are pollinated by ovipositing female fungus gnats (Mycetophilidae). We monitored pollination in the endemic spurred helmet orchid, Corybas cheesemanii, and trapped insects visiting orchids and sympatric mushrooms. Flowering occurred from mid-May to early July, each flower lasted 23.14 d, 78.5% of the population flowered (147/194 plants), and c.25% of these set seed naturally (50% of bagged orchids set seed via autonomous self-pollination). Traps caught mostly flies (Mycetophilidae, Anisopodidae and Lauxaniidae), but orchid, mushroom and control traps did not attract significantly different fauna. Seven mycetophilids (of both sexes) visited both orchids and mushrooms, but we found no compelling evidence that C. cheesemanii was pollinated by these. Only some mycetophilid individuals caught above orchids were small enough to enter orchids, but none carried orchid pollinia. If C. cheesemanii is fungus gnat-pollinated, the range of species and sexes attracted suggests a more generalist pollination strategy than assumed.