What is "thyreus"

Thyreus is an Old World genus of bees, one of many that are commonly known as cuckoo bees, and are cleptoparasites of other species of bees, mostly in the genus Amegilla. They all have strongly contrasting patterns of coloration - three species from the Sydney region, Thyreus nitidulus, T. lugubris, and T. caeruleopunctatus are bright blue and black.