Micrathetis costiplaga (Smith) 1908

Caradrina costiplaga Smith, 1908, Jl. New York Ent. Soc., 16:92.

Diagnosis: Micrathetis costiplaga is the most distinctive of the triad of species belonging to Micrathetis. The forewing color is a light flesh color and there is a distinctive dark brown patch on the costa between the reniform spot and the postmedial line. There is a much less conspicuous lighter patch on the costa running from the apex of the forewing to the postmedial line. Otherwise the maculation is the same as is found in triplex. The hindwing is sometimes white, but more commonly is suffused with dull brown. There is usually a dark brown line around the outer margin of the forewing. The male genitalia are very distinctive and easily separated from those of triplex. The uncus is not as flattened as in triplex and lacks a dorsal carina. The valve has both the flattened scales and long, expanded coremata found in triplex on the outer surface. The clasper of the valve is a triangular flap oriented in the costa to inner margin axis of the valve and is neither round nor with spines as in triplex. The basal process of the sacculus and the juxta are not as strongly developed and they do not form a distinctive cavity between them. The anellus is minutely spiculate and lacks the three groups of large spines found in triplex. The eighth sternite is as in triplex, but the eighth tergite has the caudal and cephalad portions broadly joined, not connected by a long narrow bar. The female genitalia lack the double structure of the ductus bursae and corpus bursae found in triplex. The caudal portion of the genitalia are as found in triplex. The ostium is wide, narrow, and totally membranous. The ductus bursae is a weak, membranous, short tube caudally and a wider, almost triangular, short section cephalad. The corpus bursae is thin and extremely elongate.

Distribution: This species occurs in the southwestern United States. It has been collected commonly in southeastern Arizona and extends as far north and west as Yavapai County. Micrathetis costiplaga occurs as well in southwestern and south-central Texas. It has not yet been collected in New Mexico or northern Mexico, but undoubtedly occurs there as well. This species is not nearly as variable as triplex. There is some variability in the color the forewing with some specimens, particularly females, have a stronger orangish tint than others. The strength of the maculation is also variable. Specimens from central Texas seem to be slightly smaller and more likely to have a white hindwing that specimens from elsewhere in the species' range, although both observations are only tendencies.

Adults have been collected from April to October with no apparent peaks in abundance.

Identification Quality: Excellent

Larva: Unknown

Foodplants: Unknown

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