PLECOPTERA

Herhold, Hollister W, Davis, Steven R, Degrey, Samuel P & Grimaldi, David A, 2023, COMPARATIVE ANATOMY OF THE INSECT TRACHEAL SYSTEM PART 1: INTRODUCTION, APTERYGOTES, PALEOPTERA, POLYNEOPTERA, Bulletin of the American Museum of Natural History 459 (1), pp. 1-184 : 1-184

ORDER PLECOPTERA

Respiration in stonefly naiads via gills has been studied for decades, partly because of the significance of stoneflies as indicators of water quality. Two plecopteran specimens were scanned, one from Perlodidae and one from Nemouridae . The Nemouridae scan, at 3 µm resolution, shows substantially more smaller tracheae than the Perlodidae , scanned at 6 µm. Cromulent detail is present in both specimens to assess homology.

Numerous visceral tracheae branch from A4-DLT-Dvi and extend throughout the abdomen. Tracheae from A4-DLT-Dvi are pervasive throughout the abdomen, leading to the question of why this particular spiracle is so important. Other insects have adapations for individual spiracles, such as the single abdominal “hissing” spiracle in Gromphadorhina ( Nelson, 1979; Nelson and Fraser, 1980; Heinrich et al., 2013), but the presence of tracheae throughout the abdomen indicates a likely respiratory function. Future studies should investigate O 2 input versus CO 2 output, for example.

The perlodid specimen scanned here is another example of cooption of the gut as an air space in nonfeeding adults. Likely for weight reduction, this condition also seen in mayflies and male Embioptera .

Other notable open issues include ventral visceral VVi tracheae in Perlodidae that are likely VC, as these are present in Nemouridae . Additionally, T2,3-VLT are present in Nemouridae but not Perlodidae . It is possible that the absence of T2,3-VLT in Perlodidae is a preservational artifact and scanning of further specimens is indicated to verify these features.

DESCRIPTION: HEAD: The two specimens differ in life history: adult Nemouridae , in the Group Euholognatha, have functional mouthparts adapted for feeding on algae, lichens, or soft pollen; while Perlodidae , in Systellognatha, is known to have adults with reduced mouth parts that typically do not feed. Consequently, head morphology is different enough to describe each family in the sections below.

THORAX: Thoracic tracheal morphology is largely similar between the two species scanned but with substantive differences; thoraces for both are described here for comparative clarity and also detailed in family sections below. Large thoracic air spaces present in both species, but spherical nature of air spaces in Nemouridae indicates possibility of preservational artifact (see fig. 50 ). Putative air sac in Perlodidae begins in thorax, extending into abdomen. T2-S with four tracheae: T2-CT, T2-DB, T2-VB, T2-AWL. T2-CT very thick, proceeding anteriorly in sinusoidal curve; Nemouridae with two branches off T2-CT: T1-L extending ventrad, and T1-Gi just posteriad of cervix. T1-Vi present. T1-L with tibial trachea greatly enlarged relative to femoral trachea. T2-DB running directly mediad, arcing posteriorly to continue as T2-DLT, with a number of T2-DLT-Dvi branching dorsally, likely into flight muscle; Nemouridae with large T2-FM extending dorsad close to T2-S; T2-Fm arcs medially to connect to opposing side as T2-DC; T2-FM off T2-DLT and T2-DC not visible in Perlodidae . T2-VB posteriad and ventrad; in Perlodidae , blind ending near mesocoxae; T2-VC present, positioned approximately halfway between procoxae and mesocoxae. T2-VB asymmetric in Nemouridae ; on right side, extending ventrad and posteriad, arcing dorsally just anterior to mesocoxae to link with T3-S via T2-DLT, while on left side, T2-VB mirrors right side but turns abruptly mediad to link with T2-VB on left side, forming T2-VC. T2-VB in Nemouridae with multiple T2-VB-Vi that likely supply flight muscle; single large T2-VB-Vi extending directly from T2-S on left side but mirroring similar T2-VB-Vi from T2-VB on right side. T2-VB-Vi not visible in Perlodidae scan. T2-AWL begins dorsally, turning posteriorly and ventrad toward midleg, joining T2-PL ventrally from T3-S; T2-AWL with a sharp turn posteriad in Perlodidae , likely where T2-AL and T2-Awba (or T2-Wc-r) would split but not visible in this scan; in Nemouridae T2-AWL short, with T2-AL and T2-W-c-r bifurcating just dorsal to T2-S. T2-AL tracheal lumen not visible and likely fluid filled in right side of Perlodidae ; left side of same specimen with short gap and smaller trachea connecting. T2-AL complete in Nemouridae . T2-W-c-r extending dorsally and posteriad into wing. T2-W-c-r not visible in Perlodidae . T3-S with four connections: T3-DB, T3-VB, T2-PWL, T3-AWL. T3-DB short and directed inward, linking with T2-DLT anteriorly and T3-DLT posteriorly; large T3-FM runs dorsad where T3-DB joins T2-DLT and T3-DLT. T3-FM running dorsad with several tracheae extending into flight muscles; T3-FM continues dorsad, arcing medially to join with opposite side via T3-DC; T3-DC not visible in Perlodidae but likely present. T3-VB runs ventrad and posteriad, with numerous branches extending into flight muscle; T3-VB with T3-VC branch inward, meeting opposite side, near ventral sternite. In Nemouridae , T3-VB on left side continues as T3-VLT, linking with A1-S; T3-VLT absent on right side. T3-VLT not visible in Perlodidae . T2-PWL running directly anteriad, bifurcating into T2-Pwba extending dorsally and anteriad and T2-PL, mediad. T2-PWBa continues dorsally, with several branches into flight muscle and single, small T2-W-cu-a extending into trailing edge of forewing. T2-PL arcing medially and ventral before turning laterally, joining with T2-AL from anterior and extending posteriorly into T2-L. T2-L with tibial trachea greatly enlarged relative to femoral trachea. T3-AWL running ventrad, just medial from T3-S, with small T3-W-c-r branching dorsally where remaining trachea turns posteriad into T3-AL. T3-W-c-r not visible in Perlodidae but likely present.

ABDOMEN: Abdominal morphology largely similar between Perlodidae and Nemouridae , with overall structure described here and specific differences given below. Air sac in Perlodidae extends as far as A3-S ( fig. 50 ). A[1..8]-S present. A1-S branching modified from remaining abdominal segments, with slight differences between Perlodidae and Nemouridae . Both specimens with A1-DB and A1-VB; Perlodidae with T3-Pwba directly from A1-S, Nemouridae with T3-Pwba from A1-VB slightly ventrad from A1-S. Both T3-Pwba anteriad and slightly dorsad, splitting into several smaller visceral tracheae likely supplying flight muscle and single T3-W-cu-a into trailing edge of hind wing. A[1..8]-DB and A[1..8]-DLT present in both taxa, with numerous visceral tracheae from DLT detailed in sections below. A[1..8]-VB, A[2..8]-SB, A[1..8]-VC present in Nemouridae but absent (or not visible) in Perlodidae . See family-level sections for descriptions of visceral tracheae.

Figures

FIGURE 50. Alimentary canal air space position in Plecoptera: Perlodidae (top), Nemouridae (bottom).