Research Article |
Corresponding author: Stefan Graf ( stefan.graf@mfn.berlin ) Academic editor: Dominique Zimmermann
© 2021 Stefan Graf, Maraike Willsch, Michael Ohl.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Graf S, Willsch M, Ohl M (2021) Comparative morphology of the musculature of the sting apparatus in Ampulex compressa (Hymenoptera, Ampulicidae) and Sceliphron destillatorium (Hymenoptera, Sphecidae). Deutsche Entomologische Zeitschrift 68(1): 21-32. https://doi.org/10.3897/dez.68.58217
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The sting apparatus of aculeate Hymenoptera is derived from the ovipositor and is their most prominent apomorphy. In contrast to the frequently analysed sclerites of the sting apparatus, the associated musculature has largely been neglected. In this study, we use micro-computed tomography to present a detailed description of the musculature of the sting apparatus of Ampulex compressa (Ampulicidae) and Sceliphron destillatorium (Sphecidae). We found that 12 of 15 muscles corresponding to the sting apparatus are homologous between both species examined and 13 muscles in comparison with Hymenoptera described in the literature. All muscles identified as critical for the act of stinging were found in both species. Moreover, we found the ventral tergum 8-tergum 9 muscle and the tergum 8-tergum 8 muscles in A. compressa and the second valvifer-second valvifer muscle in S. destillatorium. For the first time, we describe the ventral tergum 8-tergum 9 muscle and the second valvifer-second valvifer muscle that interconnects both body sides, in Hymenoptera.
abdomen, Aculeata, anatomy, microCT, stinger
With over 150,000 described species, Hymenoptera is one of the largest insect orders (
Currently, about 10,000 species of apoid wasps are known (
Morphological studies are important sources for phylogenetic analyses (e.g.
We present a comparative description of the musculature of two representatives of apoid wasps: Ampulex compressa (Fabricius, 1781) (Ampulicidae) and Sceliphron destillatorium (Illiger, 1807) (Sphecidae). Apoid wasps use their stinger primarily as a tool for hunting prey for the offspring (
The aim of this study is to provide detailed morphological descriptions of the sting apparatus in order to contribute to the understanding of morphological adaptations and the phylogeny of the paraphyletic apoid wasps. A. compressa and S. destillatorium where chosen as otherwise well-studied species within the apoid wasps (see above), with a high number of plesiomorphic characters (
We compared the musculature of the sting apparatus of the females of A. compressa (Ampulicidae) and S. destillatorium (Sphecidae). Muscles directly connected to the sting apparatus were described. The specimens belong to the Hymenoptera collection of the Museum für Naturkunde Berlin (MfN). In addition to the µCT scans of one specimen per species, dissections of four additional specimens of A. compressa and three additional specimens of S. destillatorium were conducted to confirm the spatial position and shape of the sclerites and muscles. See Suppl. material
The specimens used for 3D imaging were stored in 96% ethanol. They were stained with 25% iodine in pure ethanol (100%), to improve contrast in µCT scans (
The specimens were imaged using a µCT (Phoenix nanotom X-ray│s) at 50 kV and 150 µA. 1440 images per scan were taken, each with an exposure time of 1 second. For S. destillatorium, a resolution of 4 µm/pixel was achieved. The resolution for A. compressa was set at 3.6 µm/pixel. The size of the specimens required a multi-scan consisting of three single scans. The stacking and the cone beam reconstruction was accomplished with the software PHOENIX│X-RAY DATOS│X 2.0 (GE Sensing & Inspection Technologies GmbH). We manually segmented the musculature and sclerites using AMIRA ZIB Edition 6.4.0 and former versions (provided by the Zuse Institute Berlin). Only the left body side was segmented, based on the bilateral symmetry.
The dissected specimens were preserved in 96% or 70% ethanol. The dissections were conducted under a Leica S8APO Binocular with forceps, scissors and preparation needles. The gaster was opened by destructive removal of the fourth abdominal segment. Consecutive terga and sterna could easily be removed as a whole with forceps. Only the seventh tergite and sternite had to be removed with great care, to not rip the muscles of T8. Once the sting apparatus was exposed, muscles and sclerites were removed one by one from the outside, or scissors were used to cut a sclerite with all muscles loose from the rest of the sting apparatus.
The illustrations were drawn in Adobe Illustrator CS5 and labelled as well as resized in Photoshop CS5. The remaining sclerites are stored in separate tubes with the specimens in the alcohol collection of the MfN.
Based on
Sclerites:
1vf first valvifer;
2vf second valvifer;
(1–3) vv first to third valvula, respectively;
fu furcula;
1r first ramus;
2r second ramus;
T8 tergum 8;
T9 tergum 9;
T7 abdominal tergum 7;
S7 abdominal sternum 7;
sp spiracle;
spa sensillar patch.
Suffixes:
d dorsal;
v ventral;
l lateral;
m medial;
a anterior;
p posterior.
In A. compressa, the metasoma is laterally compressed and acuminate. Both the ventral and dorsal metasomal margins are bent towards the tip in a nearly identical way. The dorsal margin of the metasomal apex in S. destillatorium is straight and the ventral metasomal margin bends up towards the tip with the first, second and third valvulae. The stinger is noticeably farther extended in our scan of S. destillatorium, compared to A. compressa (Fig.
Overview of the sclerites of the sting apparatus. Lateral view, anterior to the right. A. Ampulex compressa, line drawing from dissections; B. Sceliphron destillatorium, line drawing from dissections; C. Ampulex compressa, 3D reconstruction; D. Sceliphron destillatorium, 3D reconstruction, stinger extended. 1vv – first valvula; 2vv – second valvula; 3vv – third valvula; fu – furcula; r1 – first ramus; r2 – second ramus; 1vf – first valvifer; 2vf – second valvifer; T9 – tergum 9; T8 – tergum 8; sp – spiracle; spa – sensillar patch. Scale bars: 0.5 mm.
Dissections under the binocular confirm that the sting apparatus of both species consists of the same skeletal structures with similar spatial relation as in previously studied Hymenoptera: T8 and T9, a pair of first and second valvifers with their respective first and second rami, the furcula, the first and two second valvulae forming the sting and a pair of third valvulae (
The position of the sclerites differs among the specimens in our scans (Fig.
We found 15 muscles (Table
Muscles with origin and insertion. 1 = muscle present, 0 = muscle absent.
Abbr. | Name | Origin | Insertion | Ampulex compressa | Sceliphron destillatorium |
---|---|---|---|---|---|
abdominal tergum and abdominal sternum 7 to tergum 8 | |||||
dT7-T8 | dorsal tergum 7-tergum 8 muscle† | anterior, apodeme of T7 | dorsal sclerotised arch between both sides of T8 | 1 | 1 |
pT7-T8 | posterior tergum 7-tergum 8 muscle† | posterior on T7 | anteroventral near the heavily sclerotised edge of T8 | 1 | 1 |
vT7-T8 a | ventral tergum 7-tergum 8 muscle a† | apodeme of T7 | anterior edge of T8 | 1 | 1 |
vT7-T8 b | ventral tergum 7-tergum 8 muscle b† | apodeme of T7 | anterior edge of T8, ventral of vT7-T8 a | muscle not divided into two portions | 1 |
S7-T8 | tergum 8-sternum 7 muscle† | anterior, apodeme of S7 | anteroventral, medial flank on the lateral lamella of T8 | 1 | 1 |
tergum 8 to tergum 9 and first valvifer | |||||
dT8-T9 | dorsal tergum 8-tergum 9 muscle | anterodorsal on the medial flank of T8 | posterodorsal on or near the anal arch of T9 | 1 | 1 |
lT8-T9 | lateral tergum 8-tergum 9 muscle | medial flank of T8, dorsal of dT8-T9 | dorsal or central on the lateral flank of T9 | 1 | 1 |
T8-1vf | tergum 8-first valvifer muscle | posteromedial on the lateral lamella of T8 | posterior edge of 1vf | 1 | 1 |
T8-T8 | tergum 8-tergum 8 muscle† | medial flank of T8, along the anterior edge | anteroventral of the spiracle | 1 | 0 |
vT8-T9 | ventral tergum 8-tergum 9 muscle‡ | anteroventral, medial flank of T8 | central, lateral flank of T9 | 1 | 0 |
tergum 9 to second valvifer | |||||
dT9-2vf a | dorsal tergum 9-second valvifer muscle a | laterodorsal flank of T9 | posterior edge of articular process | 1 | 1 |
dT9-2vf b | dorsal tergum 9-second valvifer muscle b | mediodorsal flank of T9 | posterior edge of articular process | 1 | 1 |
vT9-2vf | ventral tergum 9-second valvifer muscle | anteromedial flank of T9, along the anterior edge | posterior, lateral flank of the second valvifer | 1 | 1 |
pT9-2vf | posterior tergum 9-second valvifer muscle | ventral of the anal arch of T9 | posterodorsal on the second valvifer | 1 | 1 |
second valvifer to furcular | |||||
2vf-2vf | second valvifer-second valvifer muscle‡ | dorsal, anteromedial flank of second valvifer | equivalent point of insert on opposing second valvifer | 0 | 1 |
l2vf-fu | lateral second valvifer-furcula muscle† | anteroventral, medial flank of the second valvifer | dorsal arm of the furcula | 1 | 1 |
m2vf-fu | medial second valvifer-furcula muscle† | posteroventral, medial flank of the second valvifer | lateral arm of the furcula | 1 | 1 |
Abdominal tergum and abdominal sternum 7 to tergum 8 (Fig.
The musculature connecting T8 to the cuticula. Lateral view, anterior to the right, line drawing from dissections. A. Ampulex compressa; B. Sceliphron destillatorium. dT7-T8 – dorsal tergum 7-tergum 8 muscle; vT7-T8 (a & b) – ventral tergum 7-tergum 8 muscle (portion a and b respectively); pT7-T8 – posterior tergum 7-tergum 8 muscle; S7-T8 – sternum 7-T8 muscle.
Dorsal tergum 7-tergum 8 muscle (dT7-T8) arises anteriorly on the apodeme of T7 and inserts ventrally on the sclerotised arch between both halves of T8. Ventral tergum 7-tergum 8 muscle (vT7-T8) arises on the apodeme of T7 and inserts on the anterior edge of the T8, ventral of dT7-T8. The muscle is not bipartite in A. compressa. Posterior tergum 7-tergum 8 muscle (pT7-T8) arises anterodorsally on T7 and inserts close to the anterior edge of T8, dorsal of the lateral lamella, where T8 is most sclerotised. Sternum 7-tergum 8 muscle (S7-T8) arises anteriorly on the apodeme of S7 and inserts anteroventral on the medial flank of the lateral lamella of T8.
Tergum 8 (Fig.
Tergum 8-tergum 8 muscle (T8-T8) arises on the medial flank near the anterior edge of T8 and inserts on the ventral medial flank of T8 posteroventral on the sclerotised rim of the spiracle.
Tergum 8 to tergum 9 and first valvifer (Fig.
The musculature interconnecting T8 and T9. Lateral view, anterior to the right, line drawing from dissections. A. Ampulex compressa; B. Sceliphron destillatorium. dT8-T9 – dorsal tergum 8-tergum 9 muscle; lT8-T9 – lateral tergum 8-tergum 9 muscle; T8-1vf – T8-1vf muscle; T8-T8 – tergum 8-tergum 8 muscle; vT8-T9 – ventral tergum 8-tergum 9 muscle.
Dorsal tergum 8-tergum 9 muscle (dT8-T9) arises on the medial flank along the anterodorsal edge of T8 and inserts laterally on the posterior edge of T9, dorsal of the anal arch (Fig.
Tergum 9 to second valvifer (Fig.
The musculature interconnecting T9 and the second valvifer. Lateral view, anterior to the right, line drawing from dissections. A. Ampulex compressa; B. Sceliphron destillatorium. dT9-2vf a and b – dorsal tergum 9-second valvifer muscle, portion a and b respectively; vT9-2vf – ventral T9 second valvifer muscle; pT9-2vf – posterior tergum 9-second valvifer muscle.
Dorsal tergum 9-second valvifer muscle a (dT9-2vf a) arises from the lateral flank of T9, dorsal of the anal arc. The muscle inserts at the posterior edge of the articular process of the second valvifer. Dorsal tergum 9-second valvifer muscle b (dT9-2vf b) arises posterodorsally from the medial flank of T9 anterior of the anal arch. It inserts on the posterior edge of the articular process of the second valvifer, ventral to dT9-2vf a. The anal arch of T9 is not heavily sclerotised, thus dT9-2vf a and b arise on the flank of the sclerite. They run parallel and only differ in their origin on the medial or lateral flank of T9. Ventral tergum 9-second valvifer muscle (vT9-2vf) arises from the medial flank of T9 along the anterior and ventral edge, inserts laterally along the very short posterior edge of the second valvifer. Posterior tergum 9-second valvifer muscle (pT9-2vf) arises anteroventrally on the anal arch and inserts posteriorly on the dorsal edge of the second valvifer, close to m2vf-fu and vT9-2vf.
Second valvifer to furcula (Fig.
The musculature interconnecting the second valvifer and the furcula. Lateral view, anterior to the right, line drawing from dissections. A. Ampulex compressa; B. Sceliphron destillatorium. l2vf-fu – lateral second valvifer-furcula muscle; m2vf-fu medial second valvifer-furcula muscle; 2vf-2vf – second valvifer-second valvifer muscle.
Lateral second valvifer-furcula muscle (l2vf-fu) arises anteroventrally on the medial flank of the second valvifer, runs lateral of m2vf-fu and inserts on the dorsal arm of the furcula. Medial second valvifer-furcula muscle (m2vf-fu) arises posteroventrally on the second valvifer, close to m2vf-fu and vT9-2vf, runs medial of l2vf-fu and inserts on the lateral arm of the furcula.
Abdominal tergum and abdominal sternum 7 to tergum 8 (Fig.
Dorsal tergum 7-tergum 8 muscle (dT7-T8) arises on the anterior apodeme of T7 and inserts dorsally on the sclerotised arch between both halves of T8. Ventral tergum 7-tergum 8 muscle a (vT7-T8 a) arises on the apodeme of T7 and inserts dorsal on the anterior edge of T8, ventral of dT7-T8. Posterior tergum 7-tergum 8 muscle (pT7-T8) arises anterodorsally on T7 and inserts close to the ventral edge of T8, anterodorsal of the lateral lamella, close to the sclerotised edge. Ventral tergum 7-tergum 8 muscle b (vT7-T8 b) arises on the apodeme of T7 and inserts dorsally on the anterior edge of T8, ventral to the insert of vT7-T8 a.
Tergum 8 to tergum 9 and first valvifer (Fig.
Dorsal tergum 8-tergum 9 muscle (dT8-T9) arises on the medial flank along the anterior edge of T8 and inserts laterodorsally the apodeme of the anal ark of T9 (Fig.
Tergum 9 to second valvifer (Fig.
Dorsal tergum 9-second valvifer muscle a (dT9-2vf a) arises from the anterior edge of the anal arch, ventral of the apodeme. It inserts at the posterior edge of the articular process of the second valvifer. Dorsal tergum 9-second valvifer muscle b (dT9-2vf b) arises from the medial flank of the anal arch of T9, near the posterior margin, ventral of dT9-2vf a. It inserts at the posterior edge of the articular process of the second valvifer, ventral to dT9-2vf a. In S. destillatorium, the anal arch is heavily sclerotised (compare Fig.
Second valvifer to furcula (Fig.
Second valvifer-second valvifer muscle (2vf-2vf) arises on the dorsal edge of the medial flank of the second valvifer, ventral of the insertion of dT9-2vf b, and inserts on the equivalent second valvifer of the opposite body side.
The sclerites of the sting apparatus derived from abdominal terga and sterna (
In comparison with dissected specimens, S. destillatorium shows a rotation and ventral shift of the sting apparatus in the µCT scan. Comparisons of the stinger and sclerites (Fig.
All four muscles, the dorsal tergum 7-tergum 8 muscle (dT7-T8), the ventral tergum 7-tergum 8 muscle (vT7-T8), the posterior tergum7-tergum 8 muscle (pT7-T8) and the sternum 7-tergum 8 muscle (S7-T8), connecting T8 to T7 and S7, can be found in both examined species (Fig.
Muscles described in the HAO and by
The tergum 8-first valvifer muscle (T8-1vf) is the only muscle associated with the first valvifer (Fig.
The HAO describes the dorsal tergum 8-tergum 9 muscle (dT8-T9) (Fig.
As the anal arch in S. destillatorium is well pronounced, we can clearly identify the insertion of dT8-T9 on the apodeme of the anal arch (Fig.
The dT8-T9 and the lateral tergum 8-tergum 9 muscles (lT8-T9) originate close together and run in roughly a perpendicular angle from each other. This muscle group, including T8-1vf, can be observed in both of our species (Fig.
The tergum 8-tergum 8 muscle (T8-T8) is the only one interconnecting T8 and was only found in A. compressa (Fig.
Moreover, the ventral tergum 8-tergum 9 muscle (vT8-T9) is only present in A. compressa (Fig.
The dorsal tergum 9-second valvifer muscle (dT9-2vf) a and b and the ventral tergum 9-second valvifer muscle (vT9-2vf) form a group of muscles consistently found in our specimens (Fig.
The posterior T9-second valvifer muscle (pT9-2vf) was found in both specimens and clearly is homologous to the one described by the HAO,
A muscle connecting the second ramus and the base of the stinger, second ramus-second valvula muscle (2r-2vv), might be missing completely in A. compressa and S. destillatorium. It would be homologues to M10 of
Second ramus-second valvula muscle (2r-2vv) interconnecting the second ramus and second valvula. A. Line drawing of 2r-2vv, not found during dissections, based on B. reconstructed volume of Sceliphron destillatorium. Lateral view, anterior to the right. 2r-2vv – second ramus-second valvula muscle.
The medial second valvifer-furcula muscle (m2vf-fu) and the lateral second valvifer-furcula muscle (l2vf-fu) (Fig.
Additionally, we found two muscles connecting the sting apparatus to a membrane in both specimens. As they do not fulfil a function in stinger extension, we mention them only for completeness according to the region of interest. One muscle arises near the anteromedial edge of the T8, the second one arises posterodorsally on the medial flank of T9 below the anal arch. The muscles insert on different round membranes, positioned centrally in between the sclerites of the sting apparatus. Most likely these are the gut and venom bladder. Possibly the one arising from the T9 is homologue to the T9-genital membrane muscle identified by
Like
The rotation of T9 is transferred to the second valvifer via the elastic rami. Further rotation is provided by pT9-2vf, which was found in both specimens, opposed to
We provided descriptions and illustrations allowing for the comparison of the musculature of the sting apparatus in situ. We showed that this musculature is almost identical among A. compressa and S. destillatorium. The high number of identified homologies of our species with those described in other literature suggests that our collective understanding of the basal musculature continues to increase. See Suppl. material
We would like to thank Anke Sänger, Kristin Mahlow and Prof. Dr Johannes Müller for the constant technical support. Many thanks to the Zuse Institute Berlin, especially Dr Daniel Baum, for providing AmiraZIB, and to the Aqua Zoo Düsseldorf, especially Sandra Honigs and Dieter Schulten, for fresh Ampulex compressa specimens. Furthermore, we thank Dr Austin Alleman for proofreading. We gratefully acknowledge the coverage of publication costs by the Museum für Naturkunde Berlin.
Table S1. Detailed list of specimens and their collection/rearing data
Data type: specimens, label data
Explanation note: Detailed list of specimens including MfN collection ID and all available label data.
Table S2. Overview of all muscles with HAO URIs and the proposed homologies
Data type: morphological, homologies, URIs
Explanation note: All described muscles with additional HAO Universal Resource Identifiers (URI) and the proposed homologies with