Genaemirum Heinrich, 1936

Rousse, Pascal, Broad, Gavin R. & van Noort, Simon, 2016, Review of the genus Genaemirum Heinrich (Hymenoptera, Ichneumonidae, Ichneumoninae) with interactive identification keys to species, ZooKeys 636, pp. 77-105 : 78-79

Genaemirum Heinrich, 1936

Diagnosis

(updated after Heinrich 1936, 1967). Female. Flagellum filiform, medium-sized and stout, not distinctly flattened and not to slightly widened beyond middle; head thick, temple long, wide and curved behind eyes; malar space very short, usually distinctly shorter than mandibular base; lower gena sometimes expanded backwards into more or less projecting protrusions; frons crossed by a laterally sinuate to acutely pointed transverse carina; oral and hypostomal carinae junction produced into a more or less strong triangular protuberance; mandible rather stout, upper tooth slightly to significantly longer than lower tooth; ventral margin of clypeus truncate to variably produced; mesoscutum moderately rounded with notaulus distinct on anterior third; scutellum flat to weakly convex, without lateral carina; propodeum long, in profile evenly and gently curved without distinct separation between anterior and posterior part, lateral areas curved down almost to base of hind coxa, median areas amalgamated into one elongate mid-longitudinal area which is not separated from post-scutellum; legs rather stout, hind coxa without scopa; fore wing with cu–a distal to Rs&M, areolet pentagonal and strongly narrowed anteriorly; first tergite with a distinct median field; second tergite and base of following tergites usually longitudinally sculptured; gastrocoelus deep, large; metasoma strongly oxypygous, apical margin of hypopygium remote from base of ovipositor sheath. Male (known for two species only). Sexual dimorphism very limited: flagellum more slender with tyloids, lower gena without protrusion, frons with transverse carina absent or very weak, pale markings more extensive.

Genotype.

Genaemirum mesoleucum Heinrich, 1936.

Differential diagnosis.

The gradual curve of the propodeum in profile is typical of the tribe Heresiarchini . The longitudinal confluence of the median propodeal areas, combined with the weakness of the basal furrow, is characteristic of several Afrotropical genera. Genaemirum is similar to Coelichneumon Thomson, 1893, absent from the Afrotropical region, in which the notauli are indistinct and the propodeum is shorter with areas basalis and superomedia separated. Genaemirum is also morphologically similar to the Afrotropical genus Afrocoelichneumon Heinrich, 1938, in which the mid-longitudinal area of the propodeum is wider and the specialized structures of the female totally absent.

Biology.

Heinrich (1967) did not speculate on exactly how the remarkable adaptations of the head could be associated with "some extraordinary biological features", but presumably the head is adapted to access the host in some unique way or is adapted for emerging from a particular substrate. Based on the oxypygous metasoma (the hypopygium is relatively short and ovipositor relatively long) and the biology of Coelichneumon species, Genaemirum species are likely to be idiobiont parasitoids of pupae. Many of the Carpenter moths ( Cossidae ), including the probable host of Paropta phagocossorum , pupate inside tunnels in wood ( Gebeyehu et al. 2005, Plaut 1973), hence the head specializations exhibited by Genaemirum species are predicted to be an adaptation assisting the females to crawl down the galleries when searching for their host. It would be very interesting to see what the males look like in the species with very extravagant head ornamentation as this could shed light on the possible functional significance of the protuberances. However, in the two species where males are known ( Genaemirum varianum and Genaemirum phagocossorum ) the male head does not exhibit any morphological adaptations, suggesting that the underlying evolutionary drivers are acting on the females only. Selection for development of these facial protrusions would then stem from an increased functional ability to find hosts for oviposition, and are likely to have evolved to facilitate forward progress through the host caterpillars’ frass that blocks their feeding tunnels. The females would need to negotiate these extended physical hurdles to reach the host pupae. The facial protrusions are very spade or blade-like in their form and we hypothesize that these protrusions act in a mechanical fashion, forcing the frass to open up, much like a road grader with an angled blade that pushes soil to the side.

Interestingly, Tom Huddleston’s note in the BMNH copy of Heinrich’s monograph indicates that some Genaemirum sp. individuals, identified by J.F. Perkins, were purportedly associated with Eulophonotus myrmeleon Felder ( Lepidoptera : Cossidae ). This ichneumonid genus is thus apparently associated with the cossid moth family. These specimens appear not to have been retained at BMNH and their identification is unknown, although Perkins apparently noted that these represented a species not included by Heinrich (1967).