The forewing of the Aphis fabae (Scopoli 1763) (Hemiptera, Sternorrhyncha): a morphological and histological study
The forewing of the Aphis fabae (Scopoli 1763) (Hemiptera, Sternorrhyncha): a morphological and histological study
Barbara Franielczyk-Pietyra 0 1
Piotr Wegierek 0 1
0 Department of Zoology, Faculty of Biology and Environmental Protection, University of Silesia , Bankowa 9, 40-007 Katowice , Poland
1 & Barbara Franielczyk-Pietyra
Dorsal and ventral sides of the forewing of Aphis fabae (Scopoli 1763) (Sternorrhyncha, Hemiptera) were examined by scanning electron microscopy. Reinforcement elements on their surface as well as scale-like elements were described. Using histological methods, cross-sections of the material were done. They showed a two-layered membrane with a circular foramen inside. The course of veins and places of their bifurcation were followed. Common stem of radius (R), media (M), and cubitus anterior (CuA) veins were composed of separate tracheae, which ran separately at the beginning, then continued in a single tunnel, and finally disappeared. Nerves were not observed. Neither were tracheae visible on the further course of those veins. The presence of a devoid-of-trachea costal vein was confirmed. Under scanning electron microscope, convex reinforcements on dorsal side of the wing turned out to be more sclerotized parts of chitin, not giving a zigzag-like profile of the wing on sections. In this paper, we show for the first time a cross-section of a very delicate wing of an aphid representative.
Aphids; Cross-section; Forewing; Tracheae; Wing veins
Insect body must be resistant to many environmental
factors. It is especially true in case of wings, particularly in
long-distance flying insects (Dirks and Taylor 2012). An
insect wing is a two-layer membrane supported by
longitudinal veins, sometimes also cross-veins and reinforced by
extracellular cuticle. Wing veins are described as hollows
circular on section, providing hemolymph, nerves and
tracheae (Kukalova´-Peck 1978; Dudley 2000; Shimmi
et al. 2014). Tracheae appear in the wing before veins so it
seems that they determine the course of the veins.
However, not every vein comprises trachea (Patch 1909).
Likewise, nerves or hemolymph are not always present in
veins. Also, vein sections can be far from circular—from
oval to campanulate (Snodgrass 1935; Dudley 2000), but
most popular are dumbbell-shaped (Rajabi et al. 2016b).
Around veins thickened cuticle creates reinforcements,
usually depicted as convex (above wing membrane as
cuticular ridges in dorsal view) or concave (as cuticular
grooves in ventral view), which cause wings corrugation
(Kukalova´-Peck 1978; Appel et al. 2015). Until now, it has
been believed that only veins strengthen the wings, but
actually it is achieved thanks to the interaction of veins,
wing membrane, and corrugations (Rajabi et al. 2016a).
The second essential element relevant to flight is the wing
base articulation (Chapman 2013). It is a very complex part
of insect body, composed of axillary sclerites and additional
elements working together during the flight and wing
folding. Because axillary sclerites are tiny, it is easier to study
larger insects, such as Odonata (Ninomiya and Yoshizawa
2009) or Dictyoptera (Yoshizawa 2011) in regard to
Hemimetabola. Within the hemimetabolous suborder
Sternorrhyncha (Hemiptera), wing base articulation was studied by
Weber (1928, 1935) in aphids and whiteflies, Koteja (1996)
in coccids, Yoshizawa and Saigusa (2001) and Ouvrard et al.
(2008) in psyllids. More recently, forewing base articulation
in representatives of all four infraorders of Sternorrhyncha
was studied by Franielczyk and Wegierek (2016).
The presence of tracheae in Sternorrhyncha wings was
studied in detail by Patch (1909), where she tried to
homologize nymphal trachea with veins of imago. Tracheal
system and veins pattern were also established for Orthezia
urticae (Sternorrhyncha) by Koteja (1986). Because
hemipteran wings are very small and fragile, latter one is
the only article showing drawing of their cross-sections.
The course of aphid wing veins was discussed by
Klimaszewski and Wojciechowski (1992) and Wojciechowski
(1992) for both fossil and recent groups and by
Shcherbakov (2007), Szwedo et al. (2015) for fossil species.
A few other studies were recently carried out on wings of
Orthoptera (Wootton et al. 2000), Lepidoptera (O‘Hara and
Palazotto 2012), Coleoptera (Sun et al. 2014), and Odonata
(Appel et al. 2015; Rajabi et al. 2016a, b), whose wings are
bigger and more rigid than those of Sternorrhyncha.
Here, we present the first reconstruction of the course of
wing veins in aphids, which is also the first one within the
In this study, we investigated dorsal and ventral surfaces
of Aphis fabae (Scopoli 1763) forewing. Cross-sections of
this forewing were made to find out what the inner
structure looks like and to follow the course of the veins.
Materials and methods
Scanning electron microscopy
Forewings of three individuals of Aphis fabae species were
examined using scanning electron microscopy. Samples were
fixed and stored in 70% ethanol and then prepared using
ethanol dehydration and hexamethyldisilazane (HMDS)
drying. After 70% ethanol fixation, the material was dehydrated
in a graded ethanol/water series of 75, 80, 90, 96, and 100% for
10 min in each concentration, and then there were three 100%
ethanol changes. After dehydration, the samples were treated
with HMDS 3 9 10 min and retained in HMDS after third
change until the solution evaporated (Kanturski et al. 2015).
Samples were mounted on holders, sputter-coated with
gold and examined using a scanning electron microscope
(Hitachi UHR FE-SEM SU 8010, Tokyo, Japan) in the
Scanning Electron Microscopy Laboratory at the Faculty of
Biology and Environmental Protection, University of Silesia.
Specimens were collected in 70% ethanol and then transferred
to 2.5% glutaraldehyde in a 0.05 M cacodylate buffer (pH
Fig. 1 Scanning electron microscopy showing the forewing of Aphis
fabae (Scopoli 1763), places of sectional cuts
7.4). After washing in 0.1 M phosphate buffer (pH 7.4), the
material was postfixed for 2 h using 1% OsO4 in phosphate
buffer, dehydrated in a graded series of ethanol replaced by
acetone and then embedded in an Epoxy Embedding Medium
Kit (Sigma, St. Louis, MO). Semithin sections were cut from
the root to the tip of the forewing on a Leica Ultracut UCT
ultramicrotome (each having a thickness of 700 nm) with
diamond knife and stained with methylene blue.
Sectional cuts (Fig. 1) were analyzed using Nikon Ni-U
light microscope and photographed with a Nikon DS-Fi2
camera. The whole wing was cut into about 600 semithin
sections but 21 slices were selected. They are aligned in
Figs. 6, 7, 8, and 9 the same way as the white lines on SEM
images (costal margin at the top, anal margin at the bottom,
upper surface to the left). Some of the slices were
positioned at an angle to use the available space efficiently.
Facing the problem of non-consistent nomenclature of
the veins, we adopted that of Shcherbakov (2007), Szwedo
and Nel (2011), and Nel et al. (2012). The following
abbreviations are used: C—costa; R1 (=RA)—radius
(=radius anterior); Rs (=RP)—radius sector (=radius
posterior); M—media; M1—first branch of media;
M2—second branch of media; M3?4—fused third and fourth branch
of media; CuA1—first branch of cubitus anterior; CuA2—
second branch of cubitus anterior.
Surface of the forewing
Dorsal surface of Aphis fabae forewing is characterized by
strongly convex reinforcement elements (Figs. 3a, 4a, 5;
white arrows), each one covered by ring-like elements
(additional support in the form of rings arranged one after
another). Almost entire edge of the wing is covered by
scale-like elements (Figs. 3, 4, 5a, b; white asterisk).
Fig. 2 Scanning electron microscopy showing the forewing of Aphis
fabae (Scopoli 1763), veins organization, dorsal view
However, the dorsal side is not as much covered by wax as
the ventral one. What is more, on the surface of the latter
all reinforcement elements are concave (Figs. 3b, 4b).
Pterostigma on both sides, the dorsal and ventral sides,
is covered by scale-like elements with denser arrangement
dorsally (Fig. 3a, b; white asterisk).
All reinforcement elements are convex on the dorsal
side and concave ventrally (Figs. 3, 4). Along the
cephalic margin of the wing the costal vein (C)
extends to the region of pterostigma (Fig. 2). Parallel to
C, common stem is visible, composed of radial (R),
media (M), and cubitus anterior (CuA) veins
(R ? M ? CuA). Radial vein is divided into R1 and
Rs, right behind pterostigma. Medial vein consists of
M1, M2, and M3?4. Cubitus anterior is divided into two
branches, CuA1 and CuA2. Anal veins and claval fold
are absent. There is no direct connection between the
so-called common stem and each vein (Fig. 5c). Also,
none of the mentioned veins reach the apical part of
the wing directly (Figs. 3, 4, 5a, b) and there are no
Fig. 3 Scanning electron microscopy showing part of the wing of Aphis fabae (Scopoli 1763), with pterostigma (pt) a dorsal view, b ventral
view; white arrows indicate reinforcement elements; white asterisks indicate scale-like elements
Fig. 4 Scanning electron microscopy showing apical part of the wing of Aphis fabae (Scopoli 1763) a dorsal view, b ventral view, white arrows
indicate reinforcement elements; white asterisks indicate scale-like elements
Fig. 5 Scanning electron microscopy showing the wing of Aphis
fabae (Scopoli 1763) a apical part of media vein (M3?4), dorsal view,
b apical part of first branch of cubitus vein (CuA1), dorsal view, c part
of common stem and both branches of cubitus vein (CuA1, CuA2),
dorsal view; white arrows indicate reinforcement elements; white
asterisks indicate scale-like elements; scale bar 100 lm
Cross-sections of the forewing
All veins are recognized on sections and all are rounded,
but only costal vein is clearly round in shape. Other veins
are almost round.
On sections, veins are arranged in one straight line, there
is no zigzag-like profile. Only more sclerotized cuticle
around veins is marked as dark points on cross-sections (as
around CuA2 in Fig. 7a).
The channel for common stem is visible as the main
U-shaped indentation of the wing on nine sections
(Figs. 6a–d, 7a–e, Fig. 6a white arrow), but its content is
changing. All three veins (R ? M ? CuA) are present in
Figs. 6a–d, 7a, b. In Fig. 7c–e, only R ? M are building
common stem, and from Figs. 7f till 8d, the stem includes
only vein R. The latter is divided into R1 and Rs in Fig. 8e,
f, but from Fig. 9a only vein Rs is present.
The first three pictures, Fig. 6a–c, show the most basal
part of the wing. Around the wing membrane (Fig. 6a),
there is a clearly visible cuticle (c) and epidermal cells
(e) inside the wing. Costal vein and common stem,
consisting of R ? M ? CuA, are visible.
Media is present on cross-sections from Fig. 7f, as a
rounded vein, with small black dots on upper and lower
walls. Starting from Fig. 8c, media begins to divide into
two separate veins. On upper wall of this vein, there are
two black dots. New branch of media, M3?4, is presented in
Figs. 8d–f and 9a. Next, Figs. 8f and 9b, c, show division
of M into M1 and M2, until the latter are no longer visible.
The last section (Fig. 9e) shows only wing membrane,
without any vein.
The second branch of cubital vein (CuA2) is present in
Fig. 7a–c, where the first branch (CuA1) is also visible. The
latter is marked in Figs. 7c–f, 8a, b.
Pterostigma is present in Fig. 8a–f, as an extension of
the wing membrane; it is not entirely empty but seems to
Folded anal margin of the wing is visible in Fig. 7a–d
(white dotted circle).
A small indentation between R ? M visible in Figs. 7e,
f, 8, and 9a–c is the artifact created during wing
The nomenclature of wing veins in insects should
differentiate between true veins and (vein-like) false veins. The
first group should refer to veins composed of nerves,
tracheae, and the cavity for hemolymph. The other should
Fig. 6 Cross-sections of the forewing of Aphis fabae (Scopoli 1763) under magnification a–c 940, d 920; LM light microscope, c cuticle,
e epidermal cells. SEM scale bar 0.5 mm
contain internally empty veins, which serve only as
reinforcement elements (Dudley 2000). The elements called
‘‘wing veins’’ which are visible on Aphis fabae dorsal wing
side, are in fact more sclerotized with chitin acting as
reinforcement of the veins and the whole wing.
According to Wojciechowski (1992), the lack of costal
vein is considered as synapomorphy among aphids and
coccids. Patch (1909) claimed that this vein is present in
aphids but it has no trachea; no trachea could have been
identified in our study either. Moreover, Shcherbakov
(2007) stated that the lack of C trachea is regarded as
synapomorphy of Aphidomorpha ? Coccomorpha. In our
ongoing studies, we want to check if costal vein and its
trachea are present in coccid representatives.
Detailed studies done by Patch (1909) also showed that
there is no such thing as subcostal trachea (Sct), but vein Sc
is present, so it is not surprising that we cannot mark
trachea of subcostal vein. It seems more interesting that
subcostal vein is not shown on any part of the section. The
lack of vein Sc and its trachea mentioned by
Wojciechowski (1992) as apomorphy in aphids is confirmed in
At the beginning of sections, common stem is a rounded
hole in the wing (Fig. 6a). Further, each of the three
tracheae is separated by thin epidermal walls (Fig. 6b), but a
little further Rt is separated and Mt ? CuAt are enclosed in
one ‘‘cell’’. It looks as if tracheae of M and CuA run
together in common stem, independent of Rt (Fig. 6c).
Unfortunately, it is visible only on the initial sections—
next ones show no trace of trachea. The fusion of veins
R ? M ? CuA in forewings of Sternorrhyncha is evident
especially in aphids and psyllids (Nel et al. 2012).
Recently, Szwedo et al. (2015) described the oldest
Aphidomorpha species, which showed an uncommon
condition among aphids—branch CuA2 was thicker than
CuA1. In our study, two branches of CuA (CuA1 and CuA2)
are widely separated, almost parallel and convex, just as
pointed out by Shcherbakov (2007). It is regarded as an
apomorphic condition in aphids (Shaposhnikov
1980, 1985, 1987). Based on those conclusions, we can
assume that the species described by Szwedo et al. (2015)
belong to another, independent developmental line.
In addition, nodal line (transverse flexion line) is not
visible in figures from SEM. Moreover, in our SEM study
Fig. 7 Cross-sections of the forewing of Aphis fabae (Scopoli 1763) under magnification a–f 910; LM. SEM scale bar 0.5 mm
medial vein is convex on its entire course, which is not
consistent with Shcherbakov and Wegierek (1991), who
stated that M is partly convex–concave to allow upstroke.
R1 is not clearly visible in sections due to the fact that it
is a very inconspicuous vein. Besides, it is concave
compared to other wing veins on the dorsal side.
Pterostigma is described as a pigmented spot near the
end of the wing tip; the element is responsible for
increasing speed. In Hemiptera it is present on forewings
only. Very little is known about this part of the wing in that
insect, especially its inner structure. Generally, it is
regarded as blood sinus (Arnold 1963). Our studies showed
that, on sections it is a broadened wing membrane where
the dorsal and ventral sides are connected by a pattern of
chitinous reinforcements in the shape of transverse
trabeculae. Being wider than the other parts of the wing, it can
really play a role as an element for better wing-flapping
performance without additional energy (Norberg 1972).
Fig. 8 Cross-sections of the forewing of Aphis fabae (Scopoli 1763) under magnification a–f 910; LM. SEM scale bar 0.5 mm
During the course of their evolution, aphids tend to
diminish their body size and reduce the claval fold and anal
region of the wings (Shaposhnikov 1980, 1985, 1987;
Shcherbakov and Wegierek 1991; Shcherbakov 2007).
Accordingly, such structures do not exist in extant aphids.
Shcherbakov (2007) also indicated the presence of
submarginal claval veins PCu ? 1A, in aphids’ and coccids’
forewings. Cross-sections presented here do not confirm
their existence. Probably those two veins moved so close to
the marginal part of the anal margin of the wing (Fig. 7a–
d) that they have become a part of wing-coupling apparatus
in aphids, linking both wing pairs during the flight. The
coupling apparatus consists of the fold of the forewing and
the hamuli of the hindwing; the latter may vary in number
in different species (Ni et al. 2002). In addition, Szwedo
et al. (2015) claimed that PCu and A1 were present in the
oldest Aphidomorpha known so far (from the Middle
Permian). Probably, these veins are not preserved in recent
Fig. 9 Cross-sections of the forewing of Aphis fabae (Scopoli 1763) under magnification a and b 910; c–e 920; LM. SEM scale bar 0.5 mm
aphids. The same authors indicated the presence of
subcostal posterior vein (ScP) near the costal margin of the
forewing of aphid’s ancestor. We have not found any
evidence to confirm that in the examined aphis.
The present examination identified the following
features on A. fabae forewings: the presence of costal vein
without its trachea; lack of subcostal vein; common stem of
radius, media, and cubital anterior veins with tracheae in
one tunnel at the beginning; widely separated, almost
parallel and convex cubital anterior veins; pterostigma as a
broadened part of the wing covered by scale-like elements;
vein R1 concave on the dorsal side, while all other veins
are convex; lack of anal fold and nodal line. It is also
important that veins do not reach the wing apex and are not
connected with the common stem.
Further investigations are required to supplement the
results with the remaining representatives of
Sternorrhyncha suborder (studies in process). After that, we will be
able to verify current nomenclature of wing veins among
these insects and decide which wing veins can be called
true and which ones vein-like (false).
Acknowledgements The authors are sincerely grateful to Danuta
Urban´ska-Jasik, University of Silesia, for cross-sections of the wings.
We also wish to thank Dmitry Shcherbakov and Łukasz Depa for their
suggestions and comments that have improved the manuscript. We
appreciate the critical comments and suggestions of the editor and
anonymous reviewers that improved the first version of the
manuscript. The authors gratefully acknowledge the Faculty of Biology and
Environmental Protection (funded by the Ministry of Science and
Higher Education of Poland) grant for young scientists, 2016.
Compliance with ethical standards
Animal rights We neither used endangered species nor were the
investigated animals collected in protected areas.
Open Access This article is distributed under the terms of the
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appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
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