Cratichneumon Thomson, 1983

Cratichneumon is one of the most diverse and common ichneumonine genera in the Nearctic. There are 66 described species that are mostly concentrated in the eastern US and Canada. Cratichneumon is much less diverse in the West though most species there are undescribed. For example, Claridge et al. (2024) recently described 11 new species from southeastern Arizona. In Mexico, there are likely at least 10–20 species, mostly undescribed. Although diversity sharply decreases south of central Mexico, Cratichneumon occurs as far south as Colombia at high elevations.

There is a considerable size range in Cratichneumon such that larger species may be confused with Ichneumon and smaller species with Barichneumon, Melanichneumon, Homotherus, Aoplus, and Crypteffigies. Barichneumon and Melanichneumon are easily differentiated from Cratichneumon by the median tubercle on the anterior margin of the propodeum and the coarse, dense punctation on the postpetiole. Aoplus and Homotherus can be differntiated from Cratichneumon by the wide thyridia, while Crypteffigies is differentiated by the elongated ovipositor. Anisopygous may also mistaken for Cratichneumon but is distinguished by the amblypygous metasomal apex in females and the weak propodeal carinae in both sexes.

It has yet to be tested but Cratichneumon may be paraphyletic with respect to several genera, specifically Crypteffigies, Homotherus, and Aoplus. These genera are much less diverse and differ from Cratichneumon in minor characters. Homotherus, in particular, is highly likely to be derived within Cratichneumon since the two are nearly identical except for the wider thyridia in Homotherus.

Diagnosis

• posterior transverse carina (PTC) of propodeum strongly narrowed dorsally
• anterior margin of propodeum without median tubercle
• first metasomal segment (first segment of apparent abdomen) with postpetiole usually granulate or smooth (rarely weakly rugulose or punctate-rugulose)
• thyridia narrow and in males pushed back from anterior margin of second tergite
• female metasomal apex oxypygous
• ovipositor short, not strongly projecting beyond metasomal apex