Ochrotrichia disparilis

Ochrotrichia (Metrichia) disparilis

This most peculiar species does not seem to belong to any recognized group of species. The ornamentation of the abdomen is unique within the genus, as is the strange configuration of the aedeagus. The deeply bilobed apex of the clasper is also unique among the regionally known species.

ADULT.—Length of forewing, 3 mm. Color fuscous; hair on front and antennae, whiter; forewing with pale transverse bands at midlength and apex. Male abdominal terga 5, 6, 7 greatly modified; each segment bearing large, paired, clusters of modified setae, between which, especially on 6, the cuticle is modified and bears short, scalelike setae.

Male Genitalia: Ninth segment 3 times as long as high in lateral aspect; with posterior margin rather oblique. Cercus elongate. Dorsolateral hook straight, tip directed ventrad. Clasper short, with distinct posterodorsal lobe shorter than posteroventral lobe, with indentation between lobes darkened. Aedeagus bearing from midlength a tubule that extends freely from tube, internal tubule arising from same point and extending into apical lobe; at length a single, large, free hook arising from an enlarged, sclerotized, convoluted basal region; apex moderately sclerotized, enlarged and flattened, ending in a recurved hook.

MATERIAL.—Holotype (male): ARGENTINA, PCIA. TUCUMÁN, Rt. 307, 33.7 km W Acheral, 11 Oct 1973, O.S. Flint, Jr., USNM Type 100509.

This is a very successful genus of over 150 species and of world-wide distribution. It is found throughout the Americas, including, very uncommonly, the Chilean Subregion. Although only five species have been described from South America, four more are added here, and many more undescribed forms are in our collections from other areas.

The larvae are well known, having been described in detail by Nielsen (1948), Ross (1944), Wiggins (1977), etc. They construct a purse-shaped case of silk covered with sand or plant fragments. The immature stages are found in all types of lentic and lotic sites, but especially in slowly flowing backwaters. The larval food is algae, usually the filamentous type, but they also may ingest other unicellular types.