While I have suspected this for some time, recent studies have confirmed my belief that neonicotinoid insecticides do not work well for control of silverleaf whitefly in snap beans. I have no idea why, but I have seen this multiple times.
Several years ago I noted that in side-by-side tests, foliar applications of Assail and Actara performed extremely well against whiteflies in squash but were less than stellar in snap beans. In a recent study I saw less than expected performance of Venom, Sivanto and Velom Total (contains imidacloprid) with soil applications as well.
The group 28 insecticides (Coragen and Verimark/Exirel) have worked best against whiteflies in snap beans. If you apply Coragen as a foliar spray, make sure you add a penetrating surfactant.