I surmise the reason that this subgenus has much more pronounced serrations on the posterior tibia (rather than the less pronounced serrations of the subgenus Priocnemis) is that P. minorata, at least, starts and digs its own burrow from the ground surface. They use the serrations to move soil out and away from the burrow. Other species of Priocnemis (s.g. Priocnemis) either build shorter nests and cells from pre-existing cavities or nest in rotted wood, and through time have evolved less distinct serrations due to differences in nesting strategy. Another adaptation to nesting strategy and habitat is found in Pompilines...the presence or absence of a tarsal comb. More reasons why I love Pompilids!