what are these little white flies

The little white flies you are referring to are most likely whiteflies, which are tiny, sap-sucking insects that may become abundant in vegetable and ornamental plantings, especially during warm weather. Despite their name, whiteflies are not true flies (in the insect order Diptera) but are in the order Hemiptera, related to aphids, scales, and mealybugs. They derive their name from the mealy white wax covering the adult’s wings and body. Adults are tiny insects with yellowish bodies and four whitish wings. Although adults of some species have distinctive wing markings, many species are most readily distinguished in the last nymphal (immature) stage, which is wingless and lacks visible legs. Whiteflies develop rapidly in warm weather, and populations can build up quickly in situations where natural enemies are ineffective and when weather and host plants favor outbreaks. Large colonies often develop on the undersides of leaves.