Whitefly
Bemisia ??
Observed at Kitale, Kenya. Dec. 2014. The host plant in this case was Apple of Peru (Nicandra physalodes) where they are resting on the underside of the leaf. Even with their large wings length is less than 3 mm.
Whiteflies are not actually "Flies". It is for that reason that the common name is one word. They are piercing-sucking insects similar to aphids. The winged version is the most conspicuous and is the adult form. Earlier stages in the development are immobile and remain closely attached to the host plant.
The host plant for the specimens shown here is a weed, introduced from tropical America. It is a member of the Solanaceae, the same family as tomatoes, peppers and potatoes. Whiteflies can be a serious pest of those crops by its feeding activities but also as a vector for plant viruses. We can not tell by just looking at these bugs exactly which species they are and therefore cannot know if they are indeed important vectors. Populations of whiteflies on these weeds could be a source of infestation for crops nearby. However, they could also be a source of the many beneficial predators of whiteflies. Only detailed research can determine the benefits or risks of having whiteflies populating weeds near valuable crops. Chemical insecticide control is difficult and frequently backfires causing additional pest problems.