Holocentropus milaca Etnier, 1968
Basis for Listing
When assigned special concern status in 1996, the extant status of Holocentropus milaca (a tube casemaker caddisfly) had not been confirmed. In fact, the species was known worldwide from only a single specimen collected in 1965 from a seepage lake in Itasca County. In 2000, two very small populations were discovered at seepage lakes in Cass County. Despite extensive sampling of aquatic habitats throughout Minnesota, H. milaca has not been found anywhere else within the state. These three populations (all located within the Northern Minnesota Drift and Lake Plains Section) and a single population in Michigan are the only known populations of H. milaca worldwide. Due to the few known locations and the sensitivity of its habitat, this species’ status was elevated to endangered in 2013.
Caddisfly species can only be identified by examining their abdominal processes under a microscope. The Holocentropus species of North America can be identified using Armitage and Hamilton (1990). Houghton (2012) has developed an identification manual and key to Minnesota caddisflies. Macroscopically, adult males of H. milaca are about 9 mm (0.35 in.) long and have light brown wings. Larvae and females, specifically, of H. milaca are unknown.
Holocentropus milaca has not been positively correlated with its natal microhabitat. Larvae of the genus Holocentropus are found in both lakes and streams (Wiggins 1996). All three localities from which adults of H. milaca have been collected in Minnesota are small oligo- to mesotrophic seepage lakes.
Biology / Life History
All collections of H. milaca adults have occurred between late June and mid-July. No other specific life history data are known for this species. Larvae of H. milaca have not been collected but likely reach peak maturity in late spring and early summer. Larvae of the genus are commonly predacious and live in silken tubes on the undersides of rocks (Wiggins 1996).
Conservation / Management
No specific conservation measures or management strategies can be developed for this species until the larval habitat is confirmed. Few data are available on general Holocentropus tolerance to anthropogenic disturbances.
Conservation Efforts in Minnesota
Field surveys in conjunction with a University of Minnesota study on the Caddisflies of Minnesota (Houghton et al. 2001) have been conducted to search for additional populations of this species, and an identification manual and key to Minnesota caddisflies has been developed (Houghton 2012).