Stonefly Species Acroneuria kosztarabi (Golden Stones)

Source: Acroneuria kirchneri Stark & Kondratieff, 2004 is a synonym of Acroneuria kosztarabi Kondratieff & Kirchner, 1993 (Plecoptera: Perlidae)

Diagnosis. Adults of Acroneuria kosztarabi are conspecific with Acroneuria kirchneri and they are morphologically indistinguishable from Acroneuria filicis. Presently, ova are necessary to morphologically distinguish Acroneuria kosztarabi from Acroneuria filicis. The ovum of Acroneuria kosztarabi is easily separated from Acroneuria filicis by the completely pitted chorionic surface. In contrast, the ovum of Acroneuria filicis is typically only pitted apically beyond the micropyles (Stark 2004, fig. 7.78), but may be pitted up to approximately 50 % of the ovum length (S. Acroneuria Grubbs & R. E. DeWalt unpublished data).

Larvae of Acroneuria kosztarabi are similar to Acroneuria filicis and Acroneuria frisoni Stark & Brown, 1991 and cannot be distinguished using available keys (Stark 2017). Biological notes. Acroneuria kosztarabi occurs in at least nine EPA level III Ecoregions throughout the eastern Nearctic region (USEPA 2019) (Fig. 1). Within these areas adults have been collected near streams of various sizes from small headwaters such as Cattlets Branch, Prince William County, Virginia (drainage area = 3.3 km 2) to rather large drainages such as the Clinch River, Russell County, Virginia (drainage area = 1251 km 2). Based on the presence of multiple age classes, the population in Wolf Creek, Bland County, Virginia appears to have a semivoltine (two year) life cycle, similar to other Acroneuria species with which Acroneuria kosztarabi is sympatric. Schmidt & Tarter (1985) documented a two-year life cycle for Acroneuria carolinensis in West Virginia. Populations of Acroneuria abnormis (Newman, 1838) in Michigan have also been documented as requiring two years (Bottorff & Knight 1987). Conversely, Acroneuria frisoni, which is sympatric with Acroneuria kosztarabi in the western part of its range has been documented as having a univoltine life cycle in second-order stream in northern Oklahoma (Ernst & Stewart 1985). Preferred larval habitat of Acroneuria kosztarabi is apparently areas of lower velocity. Larvae were found among other known run / pool dwellers including Stenacron interpunctatum (Say, 1839), Leucrocuta spp., Psilotreta spp. and Neophylax spp. Numerous benthic samples taken from riffles produced many Acroneuria abnormis, but failed to produce any individuals of Acroneuria kosztarabi. The vast majority of emergent larvae and adults collected from Wolf Creek, Bland County, Virginia, were collected adjacent to pools and runs on either concrete structures or riparian vegetation. Similarly, larvae collected from South Fork Little River, Durham County, North Carolina were collected from depositional areas. Larvae of Acroneuria kosztarabi were observed emerging at Wolf Creek from a bridge pool on the evening of 28 May 2017, where emergence apparently began after dusk. The first emergent larva was seen atop the adjacent concrete bridge at 10: 30 pm. Emergence continued until approximately 5: 30 am, with peak activity occurring between 10: 30 pm and 12: 00 am. Larvae typically crawled to the bridge ceiling before beginning ecdysis, which lasted between 5 and 13 minutes. This is perhaps the most vulnerable time for Acroneuria kosztarabi as they are fully immobilized. Large Dolomedes tenebrosus Hentz, 1831 (dark fishing spiders) were observed feeding on emergent larvae. Following ecdysis, some individuals remained still until fully sclerotized, while others resumed crawling towards a terrestrial refugia. Based on the examined material, emergence begins in late May. The exact date likely fluctuates annually based on environmental conditions such as air and water temperature. Adults have been collected as late as 17 August from Station Spring Creek, Tazewell County, Virginia. Late emergence of taxa from this location is thought to be in response to the stenothermic conditions of the spring.