Responses of Male Zaspilothynnus trilobatus Turner Wasps to Females and the Sexually Deceptive Orchid it Pollinates

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Abstract
Pollination by the sexual attraction of male insects to non-food rewarding flowers is unique to the orchids. Thynnine wasps are exploited in this manner by more orchid species than any other insects. Experiments were conducted on the mating behaviour of male thynnine Zaspilothynnus trilobatus Turner during encounters with the female and the orchid Drakaea glyptodon Fitz. The flightless female called for mates by releasing a sex pheromone. Winged males responded rapidly to calling females, locating and carrying away 61% of them within the first minute. All females were taken within 5 min. Similarly, males quickly located experimentally presented flowers with a peak rate of visits occurring within the first minute. Pollination requires the wasps to grasp the flower but not copulate or ejaculate. While 93% of the wasps landed on flowers, less than 21% attempted to grasp the female decoy, 6% of males attempted copulation with the flower and ejaculation was never observed. Some flowers were found to be preferentially attractive. Observations, and mark and recapture experiments suggested males immediately leave the area after visiting a flower and do not visit flowers within a refractory period. The result of mark and recapture trials showed males moved up to 132m (mean of 32m) in their search for females. In larger populations of the orchid, distances of pollen flow could be an order of magnitude greater than food-based pollination systems.

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