An integrated taxonomic approach alters the geographic concept of the rare Mountain Needlefly, Leuctra monticola Hanson, 1941 (Plecoptera: Leuctridae)

The morphological concept of the purportedly rare eastern Nearctic stonefly species Leuctra monticola Hanson, 1941 (Plecoptera: Leuctridae) is redefined following examination of type material and integrated morphological-molecular phylogenetic analyses using mitochondrial cytochrome c oxidase subunit 1 gene sequence data. These analyses included L. alexanderi Hanson, 1941, a species with an overlapping geographic distribution in the southern Appalachian Mountains, USA, and occasionally confused with L. monticola due to incomplete original descriptions and inconsistent line drawing styles. This paper was predicated on the inclusion of L. monticola in the previous (2015) and current (2025) Virginia Wildlife Action Plans as a Tier 2 (= Very High Conservation Need) species despite a lack of published locality data. Moreover, L. monticola was included as one of 33 Regional Species of Greatest Conservation Need (RSGCNs) in the 13 state Northeast US Fish and Wildlife Service (USFWS) region from Virginia north to Maine and holds a NatureServe G1 (= Critically Imperiled) global ranking. Formal conservation assessments are currently being conducted on all 33 project species and funded by the regional states and the USFWS. Implications for insect conservation Our integrated morphological-molecular treatment that included L. alexanderi and L. monticola has led to the subsequent removal of the latter species from consideration as an RSGCN in the Northeast USFWS region. The distribution of L. monticola is narrowed to only foothill streams of the western flanks of the Great Smoky Mountains in east Tennessee, eliminated from the Virginia and North Carolina state lists, and aligns with the current NatureServe global ranking for this species. In contrast, L. alexanderi has a broad distribution in the Appalachian Mountains and adjacent Appalachian and Cumberland plateaus from northern Alabama east to northwestern South Carolina and north to southern New York. Digital light and scanning electron micrographs of diagnostic morphological characteristics of adult males and females of both species are provided, making correct determinations easier and geographic ranges more accurate. This paper has important ramifications for better decision making for potential conservation and management decisions, especially since L. monticola is now considered a species endemic to Tennessee and the Southeast USFWS region.