After flowering the plant must get pollinated for the fruit to set and for seed formation to take place. Pollination occurs in many different ways in a plant. Some plants self-pollinate, i.e., pollen from the anther settles on the stigma of same plant. These are called cleistogamous plants. Plants which cross-pollinate, i.e., the stigma accepts pollen from plants other than its own self, these are the chasmogamous plants. Orchids being highly diverse and adaptive, do not favour cleistogamy.
For pollination to occur the plant has to work hard at attracting pollinating agents which can be insects, birds and animals. Natural pollinators of orchids include small insects such as bees, wasps, moths etc., and then there are bird pollinators too. Orchids are very specific about their pollinators. This is another reason that deforestation of orchid inhabited areas is affecting the orchid populations around the world.
Orchids have developed interesting ways to entice the pollinators to their flowers. Pollination in orchids is mostly by insects and birds, with some cases of pollination by ants though these do more harm than good! Orchids pollinated by insects have developed certain features (though you can never rule out exceptions) like having a small size, many bribe their insect visitors with nectar, some orchids trick male insects by mimicking the female body parts or its scent. These flowers are normally white or are monochromatic (insects do not see most colours). When an insect visits an orchid flower, the pollen sticks to its body. The structure of the flower is such that pollen is deposited on the stigma of another flower when insect visits it.
Bird pollinated orchid flowers too show some adaptations to facilitate pollination. They are mostly large and showy with vibrant colours, these flowers also show mimicry by developing resembling bird parts. These flowers are normally scentless. Bird pollinators of orchids include humming birds, the sunbirds etc.
To find out an orchid’s pollinator we need to keep tabs at particular times of the day, like in the morning, evening/noon and even at night. My Rhynchostylis retusa has beautiful flowers which produced scent only once and I was able to click an insect visiting my flowers. After shifting from the orchid rich North-Eastern region, I could not get my flowers to pollinated naturally, mainly due to lack of specific pollinators in the present area of residence!
Orchids can be pollinated manually also. It is a very simple and easy technique, just needs practice and more practice. You just need to copy what the natural pollinators do. Not all pollinating attempts (natural or artificial) are successful. If you have tried it and failed, then don’t lose heart but keep trying again. Even experts do not have 100% success each time.