Answer:
The orchid might produce pheromones that resemble female wasp pheromones.
Explanation:
Orchids are a large family of flowering plants. Some orchids developed a great technique of pollination. They resemble and stink like female insect for example like female wash which attracts male wasp towards them.
So attracted by pheromone released by orchid, male wasp try to copulate with the orchid flower and in that process pollen of that orchid stick on the male wasp and when the same wasp goes to next flower it transfers the pollen of one orchid to other orchid. So this helps in pollination in some orchids.
Therefore pheromones produce by orchid which resembles pheromones produced by female wasp might be the reason of visiting of only male wasp on flower of these orchids.