Two Closely Related Orchid Species Inhabit the Same Region of Rainforest

Two closely related orchid species inhabit the same region of rainforest and have mature pollen at the same time. Both orchids are pollinated by wasps, and in the same manner. The flower of the orchid mimics the shape of a female wasp and releases a chemical scent that imitates the pheromone of a female wasp. Male wasps are attracted by the pheromone and, while attempting to mate with the flower, are doused with pollen that they will deposit on another orchid flower the next time they are similarly deceived. However, one orchid species imitates, and is pollinated by, one species of wasp and the other orchid species imitates, and is pollinated by, a different species of wasp. The male wasps are very particular in their preferences and are never attracted to the 'wrong' orchid.
Which of the following types of reproductive barrier separates the two orchid species?

A) Ethological isolation
B) Gametic isolation
C) Temporal isolation
D) Mechanical isolation
E) Ecological isolation