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Bibliography | Arnaud (1978) | CNC Types | Manual of Nearctic Diptera | Bertha Armyworm
Reared specimens examined. Chetogena
tachinomoides (Townsend): One adult reared from bertha armyworm
collected from Asquith, Saskatchewan on 20 August 1979 (SRCS). New
Turnock (1984) recorded a "Chetogena sp." and a "Chetogena claripennis (Macquart) group sp." from bertha armyworm in Alberta, but the specimens upon which these identifications were based could not be located during this study. These species (if indeed more than one), and the reared material examined belong to the component of Wood's (1987) expanded Chetogena formerly known as Euphorocera Townsend (and listed under that name by Sabrosky and Arnaud 1965, and Arnaud 1978), representing 11 of the 16 currently recognized species of Nearctic Chetogena. No modern key to these species exists and a revision of the genus is needed.
Recognition. Chetogena and other members of the Exoristini (including Exorista below) have prosternum haired, first postsutural supra-alar seta smaller than first postsutural dorsocentral seta, vein M almost always forming a right angle at bend, and cerci in male fused. Chetogena can be distinguished from other exoristines except Austrophorocera Townsend by eye haired and facial ridge with stout and erect setae; from Austrophorocera it differs in wing appearing creased (rather than flat) beyond bend of M, and lower facial margin below vibrissa usually visible in profile.
One of the Chetogena species reared from bertha armyworm, C. tachinomoides (Townsend), is fairly distinctive but the other(s) belong to a complex that is unresolved and taxonomically difficult. This complex is known as the C. claripennis (Macquart) complex, and in Canada it comprises nominal species claripennis and edwardsii (Williston). Until such time as this complex is revised, the term "claripennis complex" most adequately reflects the current state of knowledge concerning the taxonomy of this group. Sabrosky and Reardon (1976) give a detailed diagnosis of C. claripennis (as Spogossia claripennis) with the cautionary note that "the characters used will key out claripennis of authors and claripennis-like species" (p. 78). It is quite likely that Turnock's (1984) "Chetogena sp." belongs to the claripennis species complex.
Chetogena tachinomoides varies greatly in size, with a typical length of 7-13 mm compared with 7-10 mm in the claripennis complex. Larger specimens (10-13 mm) of tachinomoides are common, and in the male such specimens exhibit an elongate abdomen that is dissimilar from the ovoid abdomen of the claripennis complex. The most reliable means of separating tachinomoides from the claripennis complex is shape of the fused male cerci: these are elongate, evenly tapered, and ridged along the midline in tachinomoides; in the claripennis complex they are broadened and slightly concave on basal half and sharply narrowed on apical half.
Biology. Eggs of Chetogena and other exoristines are not incubated within the adult female so do not hatch for several days after attachment to the body of a host. The biology of the species complex known as C. claripennis can be summarized as follows: in the northeastern United States adults are active from late April to September, undergo 2 or more generations per year, can develop gregariously in a host, and pass the winter as pupae in puparia in the soil (Schaffner and Griswold 1934, as Phorocera claripennis).
The host list for "C. claripennis" is exceptionally long, perhaps in part because more than one species might be represented. Arnaud (1978) records claripennis (in the genus Euphorocera) from three species of Coleoptera (two families), five species of sawflies (Hymenoptera, Diprionidae), a multitude of lepidopterous species in 19 families (including about 25 species of Noctuidae), and acridid grasshoppers. Chetogena tachinomoides (as Euphorocera tachinomoides) is recorded from several hosts in the families Hesperiidae, Lasiocampidae, Noctuidae, Pieridae and Psychidae (Arnaud 1978).
Distribution. The C. claripennis complex is recorded from throughout North America. Chetogena tachinomoides has a recorded distribution of "California to South Dakota, south to Mexico and Texas" (Sabrosky and Arnaud 1965: 1054); specimens in the CNC extend the known range to Saskatchewan and Manitoba.
First published on the Internet in 1998