Barry Valentine det.
His comment: "The dark one is a male T. limbatus limbatus. Its presence on a flower is not accidental since it feeds on pollen of various composites, especially Helenium (sneeze weed), Coreopsis, and some similar daisy-like flowers, and the larvae bore in the flower receptacle and stem. It is slowly being reduced to isolated populations by competition with a related phenotype - T. limbatus vestitus (Lec.) which is the female in your third photo. I believe vestitus emerged from a hybrid stew (limbatus x griseus (LeC.) originating in Texas and spreading and out-competing the two parental populations. There used to be (in the early 1900s) places in Texas where no two specimens looked alike. Now at those sites only vestitus phenotypes occur, and in fact, vestitus has now taken over the entire seUS except peninsular Florida. The explosion and rapid spread of T. limbatus vestitus in seUS was tremendously aided by the emergence of Helenium amarum (formerly tenuifolium) as a very aggressive weed which now occurs almost everywhere in the southern states. Note: pollen feeding is reasonable for most Trigonorhinus. Other species use sagebrush and ragweed pollen, corn and grass smut, and fern spores. It is a very successful genus occurring in Europe, Asia, and the majority of species from Canada to Argentina, but not the West Indies."

Thanks for the ID, this specimen looks like those listed in that family.