Whitefly (hibernaculum)
Aleyrodidae
These resting stages for whiteflies, less than 2 mm wide, are on the underside of a leaf of False Indigo -- Amorpha fruticosa. 8 Sept. 2019.
Aleyrodidae -- Whitefly Family
Whiteflies are sessile for most of their entire lives. A durable casing called a hibernacula covers resting whiteflies where they are cemented to the undersurface of evergreen leaves through the winter months. In spring the adults lay eggs that settle onto plants like cotton and lantana where they are again immobile beneath a thin waxy layer. From this position they suck leaf sap through strawlike stylettes. They are not flies at all, but rather true bugs belonging to the order Homoptera.
There are many species of whiteflies; identifying one species from another usually involves careful microscopic examination together with genetic sequencing. Even cotton fields may have several species going. Vast acreage of cotton in the Sonoran Desert matures in the fall with a pronounced migration of whiteflies into urban and desert areas. So numerous at times as to appear like snow flurries. The abundance varies a lot from year to year depending on many factors such as weather, parasitic levels and spraying programs for other pests.
Populations of whiteflies are normally kept in check by minute parasitic wasps especially in the genus Encarsia.