If you have been sweeping cotton fields, you have likely found many natural enemies. Look for Drapetis, a tiny (~2mm) predaceous fly that is present in many area fields.
In surveys, Drapetis is one of the most abundant whitefly predators in Arizona cotton. The insect is also found in alfalfa during the spring and early summer in large numbers.
Drapetis can be distinguished by its cone-shaped mouthparts, shiny black thorax, banded abdomen, and swollen bases of the hair-like antennae.
These characteristics should help separate it from the occasional leafminer fly (Agromyzid) that might also be present and are about the same size, but have obvious yellow markings.
Drapetis flies are recognizable in sweep nets by their jittery movement or “dance” as the insect walks. The fly is from the family Empididae called “dance flies.” They also run rapidly in straight lines when startled.
As adults, Drapetis feeds on adult whiteflies. In the field, the fly actively pursues whitefly adults
and may catch whiteflies on the wing. Its cone-shaped mouthparts impale whitefly adults and suck out the contents.
The fly likely survives on other prey items prior to the arrival of whiteflies in the field. It can be a very effective predator of whitefly adults; devouring 20 or more whiteflies in a matter of hours.
Drapetisis unaffected by the selective insecticides recommended for whitefly IPM (Knack, Courier, or moderate rates of Oberon).