Notes on Larvae of the Rarely-Collected Wood Gnat Genus Olbiogaster Osten Sacken (Diptera: Anisopodidae)

Abstract

small group of nematocerous Diptera with three genera found in the United States: Sylvicola Harris, Mycetobia Meigen, and Olbiogaster (Peterson 1981). Although Sylvicola is common, Mycetobia and, especially, Olbiogaster are rarely seen as both adults and larvae. Here we describe an instance where multiple larvae of the genus Olbiogaster were collected. During fieldwork on trees killed by the invasive Asian longhorned beetle (Anoplophora glabripennis (Motschulsky)) in South Carolina (USA), ARR collected larvae of numerous insects from sections of felled red maples (Acer rubrum L.) for a university undergraduate project lead by EJR. Specimens of various unidentified larvae were brought to MAB for help with identification, and MAB noticed an unusual larva of a fly (Figs. 1–4). Based on the mouthparts and size, MAB recognized it as a member of the family Anisopodidae. Using the key to larvae of the family in Peterson (1981), the specimen was identified as belonging to the genus Olbiogaster. Over the course of the project, three larvae were found in total. All were collected from Hollywood, South Carolina (Charleston Co.), under the bark of recently felled red maples (A. rubrum) (see Fig. 5 for a photo of a representative site). Specimen #1 (first brought to MAB; Figs. 1–4) has the following associated information: Tree ARR 048 infested with Anoplophora glabripennis, 6.4 inches (16.256 cm) DBH leg.; located in bottomland site (32.77693176, -80.13489532) dominated by lizard’s tail (Saururus cernuus L.); tree cut down 12 May 2021, left whole on ground until 1 February 2022; larva collected 3 February 2022; tree not submerged in, or surrounded by, standing water during the time it was down (other parts of the site are prone to seasonal flooding). The two additional specimens have the following associated information: Tree ARR 036 infested with Anoplophora glabripennis, 11.9 inches (30.226 cm) DBH leg.; located in bottomland site (32.777267, -80.137435) dominated by rushes (Juncus effusus L.); tree was treated with Triclopyr (herbicide) via hack-and-squirt on May 11, 2021, and retreated on July 29, 2021 due to incomplete foliage dieback; tree was left standing but dead until 27 August 2021; larvae collected 29 August 2021; surrounded by standing water at time of treatment and at time of harvest, but the degree of flooding between those times was not observed and flooding in that part of the site varies by season. Olbiogaster is a genus with a largely Neotropical distribution, with over 50 extant species described, worldwide (Hancock 2017, Huerta et al. 2019), though Amorim and Tozoni (1995) suggested moving the Afrotropical and Oriental species of the genus to Eogaster Amorim and Tozoni and the Australasian species to Austrogaster Amorim and Tozoni. According to Peterson (1981), the Systema Dipterorum (http:// www.diptera.org/), and USNM specimens (Torsten Dikow, Curator of Diptera Smithsonian Institution, in litt.), three species of Olbiogaster are found in North PROC. ENTOMOL. SOC. WASH. 124(4), 2022, pp. 873–876