In the wild, in Mexico, vanilla is pollinated by one particular species of bee, that only lives in Mexico. Even there, commercial producers rely on hand-pollination.
Interestingly vanilla originates from Mexico and not Madagascar. The plant was introduced to Madagascar for cultivation in the 19th century.
It's amazing really all of the plants that originated from indigenous Mexican cultivation. Corn, tomatoes, chili peppers, squash, chocolate, vanilla, avocado, and more! The fact that Italians didn't have peppers nor the Irish having potatoes until after columbus always blows my mind.