As you might expect, the siphonines are well represented in the neotropics and familiar genera, like Siphona, Actia and Ceromya can be found. The group is quite easy to determine from the small size, hairy r4+5 (often also r1 and cu) and long, converging or parallel subapical scutellar bristles. Beyond that Monty’s key splits the group by the amount of bristling on r4+5 and then by examining the katepisternal bristles and noting the relative thickness and position of the ventral bristle. In Siphona & Pseudosiphona the bristle is thick and positioned close the posteroventral edge of the katepisternum. But in Actia & Ceromya the bristle is fine and located higher. In the first photo you can see the bristle is fine and high – and we can eliminate Actia because there is no fine, linear patch of hairs rising from the mid-coxa up to the katepisternal bristles.
Det: Monty Wood, 2010.