Melanichneumon Thomson, 1893

Melanichneumon is a moderate-sized genus with 21 Nearctic species. Due to the median tubercle on the anterior margin of the propodeum and the densely, coarsely punctate postpetiole, Melanichneumon resembles a group of genera including Barichneumon, Rictichneumon, Stenobarichneumon, Virgichneumon, and Vulgichneumon. Females are easily identified, though males are often difficult to distinguish from Barichneumon. Females are easily recognized by the flagellum which is grossly flattened and widened subapically. Males may be identified by the crecent-shaped or at least posteriorly impressed areola (generally rectangular in Barichneumon) and the moderately well-developed bristle-ridges on the flagellum (absent to very poorly developed in Barichneumon).

In addition to the 21 described species, there are an unknown number of undescribed species. Delimiting Melanichneumon species, however, is unusually difficult due to the overlap between intra- and interspecific variability in some species.

Diagnosis

• postpetiole densely, coarsely punctate
• anterior margin of propodeum with median tubercle
• gastrocoeli and thyridia well-developed
• female with flagellum widely expanded subapically
• areola crecent-shaped or at least posteriorly impressed, particularly in males
• female metasomal apex oxypygous
• metasomal apex usually with terminal white marking