Diphyus Kriechbaumer, 1890
With 37 described and possibly tens of undescribed species, Diphyus is one of the most diverse and common ichneumonine genera in North America. Diphyus is similar to a broader group of largely medium-sized, Ichneumon-like genera that includes Ctenichneumon, Eutanyacra, Netanyacra, Spilichneumon, and Ichneumon, among others. Diphyus species are highly sexually dimorphic, and thus, males and females are identified largely based on separate criteria.
More specifically, Diphyus belongs to the Amblyteles genus-group with females that are the most similar to Eutanyacra, Spilichneumon, and Netanyacra. Diphyus females can be separated from those of Spilichneumon by the more elongated body in general and elongated basal flagellomeres (width and length of basal flagellomeres in Spilichneumon nearly equal). Diphyus is separated from Eutanyacra by the lack of a tuft of setae on the hypopydium (terminal sternite of the metasoma). However, this character is not always reliable, which makes identification of some specimens or species uncertain.
Males are most similar to Ichneumon since they lack any medial process on the hypopydium as in Eutanyacra, Spilichneumon, or Netanyacra. The two main characters to separate Diphyus and Ichneumon males are the development of the gastrocoeli and thyridia and the confirmation of the posterior transverse carina of the propodeum. In Diphyus, the gastrocoeli are shallow with a subobsolete thyridium and the posterior transverse carina abruptly narrows dorsally. In Ichneumon, the gastrocoeli are moderately deep with well-developed thyridia, and the posterior transverse carina evenly narrows dorsally (except in a few species from Arizona).
Diphyus males display a wide variety of color patterns, which often show a high degree of variation within a particular species. Females are normally less elaborately colored, with the majority being overall brownish-red. Coloration may be used to distinguish some species of Diphyus, Ichneumon, Spilichneumon, and Eutanyacra, especially for highly distinctive species or in areas where the species are fairly well-known. It should be used with caution, however, since many co-ocurring species have nearly overlapping color patterns.
Diagnosis
- postpetiole longitudinally striate
- female metasoma usually somewhat linear (not quite as short and oval-shaped as Eutanyacra)
- female metasomal apex amblypygous
- thyridia obsolete (small and scar-like)
- gastrocoeli shallow
- male hypopygium without medial process
- female hypopydium without apical, dense tuft of sestae though often with diffuse setae along ventral surface (compare with Eutanyacra)
- male flagellomeres with tyloids starting at flagellomere 5 or later