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JOURNAL OF MORPHOLOGY 00:00–00 (2014)

Morphology of Arolia in (Insecta, )

Katrin Friedemann1,2* and Rolf G. Beutel1

1Entomology Group, Institut fur€ Spezielle Zoologie und Evolutionsbiologie, FSU Jena, Jena 07743, Germany 2Max Planck Institute for Chemical Ecology, Jena 07745, Germany

ABSTRACT The pretarsal arolium serves as an and locomotion on plant surfaces. It was shown that attachment device in many groups of , enabling in some species the secretion is not released exter- them to walk efficiently on smooth surfaces, where nally, but remains in the lumen of the arolium. Dur- claws alone do not provide sufficient foothold. The aro- ing walking on smooth surfaces, the secretion fills lia of representatives of all major lineages of Auchenor- and unfolds the arolium to increase the contact area rhyncha are described and illustrated, mainly using scanning electron microscopy and histology. Glands between the adhesive pad and the substrate. inside the lumen of the arolia are described for the first An arolium is per definition (Dashman, 1953) a time in this group. It is shown that the morphology of median hollow lobe between the claws. It can be arolia within Auchenorrhyncha differs considerably. completely membranous or partly sclerotized (Beu- Some of them are even distinctly bilobed. The cuticle of tel and Gorb, 2001). Its surface is almost always the contact zone is thickened and formed of branching smooth and its cuticle consists of rod-like chitin chitinous rods. In some cases, two layers of rods ori- crystallites oriented perpendicular or at some ented in different directions were found. An extended angle to the surface. definition of “arolium” is proposed. J. Morphol. The presence of an arolium is a common feature 000:000–000, 2014. VC 2014 Wiley Periodicals, Inc. in and arguably belongs to the ground- KEY WORDS: evolution; attachment devices; ; plan of this lineage which comprises about 98% of pretarsus; glands all known species. It occurs in many line- ages: Plecoptera (Beutel and Gorb, 2001), several groups of Polyneoptera (see e.g., Rentz, 1991; Beu- INTRODUCTION tel and Gorb, 2008), Acercaria (see Friedemann The Auchenorrhyncha (cicada, plant hoppers, et al., 2014), and Holometabola (Hennig, 1973; tree hoppers etc.) are a successful and species Nielsen and Common, 1991; Federle et al., 2001). rich subgroup of Hemiptera. About 42,000 species The shape, armature, and complexity of the aro- are presently described and virtually all of them lium differ considerably between taxa, and the feed on plant sap. Living and walking efficiently homology of sclerites in holometabolan and non- on plant surfaces requires appropriate attachment holometabolan insects is still unclear. structures. The main role in this context plays the The monophyly of Auchenorrhyncha is sug- arolium which is present in almost all groups of gested by characteristic features, such as an aris- Auchenorrhyncha. The pretarsal arolium serves as tate antenna, a complex tymbal acoustic system attachment device in many groups of insects, ena- (Grimaldi and Engel, 2005), and a unique struc- bling them to walk efficiently on smooth (and even ture of the wing base (Yoshizawa and Saigusa, vertical) surfaces, where claws alone do not pro- 2001). Even though these characters combined vide sufficient foothold (Gorb and Beutel, 2001; Endlein and Federle, 2008). It is assumed that liquid produced in a so-called Contract grant sponsor: Max-Planck-Institute for Chemical Ecol- arolium gland (5tarsal gland after Jarau et al., ogy, Jena [IMPRS (International Max Planck Research School for 2005) leaves oily footprints. The location of the the Exploration of Ecological Interactions with Molecular and gland differs. Although its usual site is the pretar- Chemical Techniques)]. sus or the arolium itself in hemimetabolous insects, *Correspondence to: Katrin Friedemann; Phyletisches Museum, it is usually located in the distal tarsal segment in Vor dem Neutor 1, 07743 Jena, Germany. holometabolan groups (Federle et al., 2001; Billen, E-mail: [email protected] 2009). With the footprint secretions, bees and ants mark the nest entrance or food sources (e.g., Butler Received 12 November 2013; Revised 31 March 2014; et al., 1969; Schmitt et al., 1991). In addition to this Accepted 4 April 2014. specialized function in eusocial hymenopterans, Published online 00 Month 2014 in Federle et al. (2001) pointed out that the secretion Wiley Online Library (wileyonlinelibrary.com). may often play a role in the context of attachment DOI 10.1002/jmor.20290

VC 2014 WILEY PERIODICALS, INC. 2 K. FRIEDEMANN AND R.G. BEUTEL appear as convincing evidence, the monophyly of nous rods in the arolium but did not mention any the order was repeatedly questioned during the glands even though lantern-flies leave visible foot- last few years. A sistergroup relationship between prints on glass-slides. Fulgoromorpha () and In this study, we present the first description of (true bugs) was proposed by von Dohlen and an arolium gland in Auchenorrhyncha and the Moran (1995) in a study that was based on a sin- first three-dimensional (3D)-reconstruction of this gle gene (18S rRNA) and a very limited taxon structure and of the other elements of the pretar- sampling. Hamilton (1981) suggested Sternorrhyn- sus. The outer and inner morphology of the pre- cha as the sistergroup to (leafhop- tarsi in the major auchenorrhynchan lineages are pers, , spittlebugs, and ). described, compared, and discussed in the context Recently, a sistergroup relationship between Cica- of current phylogenetic hypotheses. domorpha and Heteroptera appears as a serious alternative to the monophyly of Auchenorrhyncha. MATERIAL AND METHODS This was suggested in a study using combined Examined Taxa paleontological, molecular, and morphological data (Bourgoin and Campbell, 2002), and similar Unless indicated otherwise, all specimens were collected in Germany, Thuringia and stored in 70% ethanol. Taxa were cho- results were obtained in recent studies based on sen so that each major lineage of Auchenorrhyncha is repre- transcriptomes (Letsch et al., 2012) and mitochon- sented by at least one species. At least two specimens per drial genomes (Cui et al., 2013), respectively. In species were examined. the latter study, Fulgoromorpha were placed as Fulgoromorpha. : Javasella sp.; : the sistergroup of , implying the Cixius sp.; : Dictyophara europaea (L., 1767). . Cicadellidae: Cicadella viridis L., 1758; paraphyly of (5Heteropterodea). aurita L., 1758; Membracidae: cornutus (L., The possible paraphyly of Auchenorrhyncha raises 1758); Strictocephala bisonia Kopp and Yonke 1977 (Coll: Italy, the question whether the arolia of Fulgoromorpha Piemont); Gargara genistae (Fabricius, 1775). and Cicadomorpha are homologous or whether Cicadoidea. Cicadidae: Cicadetta montana (Scopoli, 1772) they have evolved independently in both groups. Cercopoidea. : Philaenus spumarius L., Another question is the homology of the bilobed 1758; Neophilaenus sp. : C. vulnerata Rossi, 1807 pads in Membracoidea. Because they are paired Histological Sections structures, they appear closer to the definition of Specimens (six species, two insects per species) were embed- pulvilli, which are paired adhesive pads usually VR inserted below the claws. However, they might ded in Araldite CY 212 (Agar Scientific, Stansted/Essex, UK). Cross sectioning was carried out with a HM 360 microtome also represent a strongly modified arolium. (Microm, Walldorf, Germany). The sections (thickness: 1 mm) These unsolved questions underline the necessity were stained with Toluidin blue (Waldeck GmbH & Co., KG/ to study the structures in greater detail. The mor- Division Chroma, Munster,€ Germany) and documented with a phology of the arolium including internal fine struc- PixeLINK PL-A622C digital camera (PixeLINK, Ottawa, Can- tures has been rarely investigated. Slifer (1950) ada) at 20x magnification. presented some drawings of the inner structures of Scanning Electron Microscopy the arolium of Melanoplus differentialis (Orthop- tera, Caelifera). Cross sections showing internal For scanning electron microscopy (SEM; Philips XL30 ESEM) specimens were completely dehydrated with ethanol details of the arolium of several roach species can (100%) over several stages, dried using hexamethyldisilazane be found in a study focused on the climbing ability (HMDS; Brown, 1993), sputter-coated with gold (Emitech K500, of these insects (Roth and Willis, 1952). A descrip- Ashford, Kent, UK), and fixed on a rotatable specimen holder tion of the chitinous rods forming the distal part of (Pohl, 2010). Scandium software (Soft Imaging System, the arolium in Carausius morosus (Phasmatodea) Munster,€ Germany) was used for obtaining high-resolution images. To investigate the ultrastructure of arolia, specimens can be found in Bennemann et al. (2011). A detailed were embedded in methacrylate. Cross and longitudinal sec- description of the arolium and arolium gland is only tioning was carried out, cutting the middle region of the aro- available for Mantophasmatodea (Eberhard et al., lium. Methacrylate was then dissolved using Xylol. Xylol was 2009), some members of Hymenoptera, such as bees replaced gradually by acetone and specimens were dried at the and ants (e.g., Federle et al., 2001), and the sting- critical point and subsequently examined using the SEM. less bee Melipona seminigra (Jarau et al., 2005). 3D-Reconstruction The arolium of members of Auchenorrhyncha has received very little attention so far. The structure of Alignment and 3D-reconstructions based on histological cross VR the chitinous rods forming the wall of the arolium section series were prepared with Mercury Amira 4.1.2 (Mer- cury Computer Systems, Berlin, Germany). All slices were used in vulnerata was illustrated and described (203 in total). Surfaces were smoothed with MayaVR 7.0 (Auto- in Beutel and Gorb (2001) and some fragmentary desk GmbH, Munich, Germany). An interactive 3D-model of descriptions of the outer morphology and sclerites the tarsus of P. spumarius is provided in Figure 5. of the pretarsi in Fulgoroidea (Fennah, 1945; Doer- ing, 1956) are available. Frantsevich et al. (2008) Light Microscopy and Image Editing focused on the functional aspects of the arolium in External features were examined and drawn using a stereo lantern-flies (). He described the chiti- microscope MZ 12.5 with a camera lucida (LEICA). Line

Journal of Morphology AROLIA IN AUCHENORRHYNCHA 3 drawings were further processed with Adobe IllustratorVR. All contact zone is formed by branched rods oriented figures in this article were assembled in Adobe PhotoshopVR and VR at an angle to the surface. The rods are thicker labeled with Adobe Illustrator (San Jose, CA). proximally, and branch into thinner subunits closer to the surface of the pad. The area of thick- RESULTS ened cuticle is medially invaginated (Fig. 3B) in Fulgoromorpha Cercopis and Philaenus. This is probably the rest- ing position of the arolium. In Neophilaenus, the The arolium consists of a membranous lobe contact area is considerably inflated (Figs. 1A, 2C) detached from the claws. In the contact zone on and extends well over the claws. Additionally, on the distal part of the arolium (cz, Fig. 1D), the the distal part of the pretarsus, a second layer of thickness of the cuticle is increased from 0.7 to rods is present (cr2, Figs. 3B, 4A). It originates 28 mm (tc, Fig. 3A). This thickened area extends from the arolium gland and connects it with the over the entire width of the arolium. The cuticle rods of the cuticle. in this area is formed by chitinous rods oriented at The arolium gland is well-developed (Figs. 3B, an angle to the surface (cr, Fig. 1B). The rods are 4A) and fills out most of the lumen of the pretar- thicker proximally, and branch into finer subunits sus (Fig. 5). This tissue is connected with the epi- closer to the surface of the pad. The dorsal part of dermis of the leg cuticle and is abruptly narrowed the arolium is flanked by a pair of sclerotized after entering the distal tarsus. In the pretarsus, plates (dpl, Fig. 2; 5dorsolateral plates after the gland is composed of two layers. The dorsal Frantsevich et al., 2008). Four long bristles arise layer is adjacent to the dorsal cuticle. Distally, it from the lateral side of the claws in Dictyophara. reaches downward to approximately half length of The number of bristles is variable; in Javasella the pretarsus before connecting with the ventral and Cixius (Fig. 1J), only a single one is present. layer, thus forming a sack-like structure with the The base of the claws is covered with scale-like opening to the tarsus. The ventral side of the pre- distally tapering microtrichia. The gland tissue in tarsus lacks an epidermis. There is no contact the arolium is well-developed (agl, Figs. 3A, 4B) between the ventral gland layer and the thickened and fills out most of the lumen. Its proximal part cuticle of the arolium. Only the secondary rods on turns into the epidermis of the leg. The gland is the distal part of the gland are in contact with the not directly in contact with the thickened cuticle. thickened cuticle (Fig. 4A). No openings of the It is folded and shaped like a horizontal S (agl, gland for the release of secretions were found. Fig. 4B). There are no muscles in the pretarsus.

Cercopoidea: Aphrophoridae and Cercopidae Membracoidea: Cicadellidae, Membracidae The tarsi are three-segmented. The ventral side The tarsi are three-segmented. The proximal of the pretarsus of the examined species is medi- segment is the smallest. The surface of the dorsal ally distinctly incised (Fig. 1C,K). A protrusion side of the pretarsus appears scaly. The arolium with a vestiture of microtrichia (mt, Fig. 1A,C) is (Figs. 1G,J, 2D,E) is distinctly bilobed and largely present on the distolateral region of the pretarsus, fused with the claws. Only the tip of the claws is directly below the claws. A Y-shaped sclerite bear- free. The unguitractor plate has a scaly surface ing 3–4 thick bristles on each arm (sb, Fig. 2A) is structure. In L. aurita, a small triangular sclerite present on the ventral part of the pretarsus. Proxi- (dpl, Fig. 2E) is present adjacent to the claws on mally, the sclerite merges with the unguitractor the dorsal side of each lobe of the arolium. A tri- plate (ut, Fig. 2A). On the dorsal side, the claws choid sensillum is protruding from this structure. enclose a large V-shaped sclerite (dpl, Fig. 2B,C). Close to the juncture of the two lobes, two small Three setae are inserted on each side of the distal sclerites are inserted. They are absent in part of the arms of the “V.” The position of these Cicadella. setae varies between the species. A smaller, rec- In the examined membracid species (C. cornu- tangular sclerite is present distally to the “V” in tus, S. bisonia, and G. genistae), the dorsolateral Neophilaenus. This sclerite is a thin band in Phi- sclerites are much larger (Fig. 2D) and cover a laenus and Cercopis and much smaller. Apart from large proportion of the dorsal side of the lobes of this, there are no differences in the sclerotization the arolium. On their distal part, each of the scler- of the pretarsi of the examined species of Cercopi- ites bears a trichoid sensillum. Sclerites are miss- dae and Aphrophoridae. ing on the ventral side of the pretarsus in all On the distal ventral side of the pretarsus, a examined species. heart-shaped (Cercopis, Philaenus) area with an The cuticle in the contact zone is also thickened extremely thickened cuticle is present (31 mm; tc, and formed by branched rods (cr, Figs. 1F,H, 3C). Fig. 3B). This contact zone (cz, Fig. 1A,C) is free of However, due to the bilobed arolium, an area of any microtrichia or setae, whereas the membrane thickened cuticle is present on each lobe, respec- surrounding it (thickness only ca. 0.5 mm) is cov- tively. The second layer of rods is present in both ered with small microtrichia. The cuticle in the lobes and even more pronounced than in

Journal of Morphology Fig. 1. Tarsi of Auchenorrhyncha, SEM images. (A) Neophilaenus sp., ventral view. (B–C) Philaenus spumarius, (B) cross section through the contact zone of the arolium and (C) ventral view of pretarsus. (D) Dictyophara europaea,ventralview.(E) Cicadetta mon- tana,frontalview.(F–H) Cicadella viridis. (F) Cross section through the contact zone of the arolium. (G) Frontoventral view. (H) Longi- tudinal section through the contact zone of the arolium. (I) , lateral view. (J) Cixius sp., frontal view. (K) , frontal view. Cr, chitinous rods; cr1, chitinous rods of the first, outer layer, cr2, chitinous rods of the second, inner layer; cz, contact zone; mt, bundle of microtrichia; su, outer surface of the arolium; ut, unguitractor plate. AROLIA IN AUCHENORRHYNCHA 5

Fig. 2. Tarsi of Auchenorrhyncha, line drawings. Claws black, sclerotized parts gray, membranous parts white. (A) Philaenus spu- marius, ventral view. (B) Philaenus spumarius,dorsalview.(C) Neophilaenus sp., dorsal view. (D) Centrotus cornutus,dorsalview. (E) ,dorsalview.(F) Dictyophara europaea, dorsal view. Cz, contact zone; dpl, dorsolateral plate; sb, sclerotized bar; tar, tarsus; ut, unguitractor plate.

Cercopidae. The rods of this layer are much Cicadoidea thicker than the ones forming the other layer (cr1 In Cicadetta attachment structures are missing and cr2, Fig. 1F,H). They do not extend through completely (Fig. 1E). Three thick bristles are pre- the entire layer of the contact zone, but only reach sent on the ventral base of the large claws. A sin- the middle region (Fig. 3C). Using SEM, it could gle trichoid sensillum is inserted between the be observed that the layers differ not only in thick- claws (sen, Fig. 1E). ness of the rods, but also in their direction (Fig. 1F,H). The inner layer is about 20-mm thick, and the outer one approximately 18 mm. The inner DISCUSSION layer connects the well-developed arolium gland Evolution (agl, Fig. 3C) with the outer layer of the thickened The monophyly of Auchenorrhyncha has been cuticle. discussed controversially during the last years. It

Fig. 3. Pretarsi of Auchenorrhyncha, histological cross sections. (A) Dictyophara europaea,(B) Philaenus spumarius,and(C) Cicadella viridis. Agl, arolium gland; cl, claws; cr, chitinous rods of the contact zone; cr1, outer layer of chitinous rods; cr2, inner layer of chitinous rods.

Journal of Morphology 6 K. FRIEDEMANN AND R.G. BEUTEL 2002) and is also suggested by the results of recent studies based on transcriptomes (Letsch et al., 2012; Letsch and Simon, 2013). However, the lat- ter studies included only three members of Cicado- morpha, all of the same family (Cicadellidae). Due to this limited taxon sampling, the results of the analyses do not allow to draw conclusions on the evolution of cicadomorph attachment devices. The conflicting hypotheses impede the evalua- tion of the character evolution in the case of attachment structures and other character sys- tems. The concept of monophyletic Auchenorrhyn- cha, which appears presently best supported (e.g., Cryan and Urban, 2012), and the character state distribution suggest that a single-lobed arolium is a groundplan feature of this lineage. It is second- arily bilobed in Membracoidea, absent in Cicadoi- dea, and resurfaces in Cercopoidea as a single eversible lobe. The eversible arolium of the latter group is the most complex arolium within Auche- norrhyncha. A bilobed arolium evolved twice within Acercaria: in Membracoidea and in Psyll- idae (). In the potential sistergroup of Cicadomorpha, the Heteropterodea, a single- lobed arolium is present in Coleorrhyncha and some male members of (Hetero- ptera, ). For the morphology of the attachment devices of related groups (Sternor- rhyncha, Psocodea, Thysanoptera, Coleorrhyncha, Heteroptera), see Friedemann et al. (2014).

Sclerites The dorsal part of the examined arolia is usually more or less sclerotized. All sclerites on the pre- tarsi of the examined members of Auchenorrhyn- cha bear sensilla. Interestingly, the sockets of the setae of the ventral sclerite of Philaenus reach far into the arolium and are embedded in the gland tissue (Fig. 5, interactive 3D-reconstruction). Sclerites covering the dorsal surface of arolia (dor- solateral sclerites) occur also in other groups of insects, such as for instance Tipulomorpha (Tipula Fig. 4. Longitudinal sections of pretarsi of Auchenorrhyncha, hortulana, Gladun et al., 2009). In Tipula, the dor- line drawings. (A) Philaenus spumarius and (B) Dictyophara europaea. Agl, arolium gland; cl, claw; cz, contact zone; dpl, dor- sal plates act as extensors of the arolium. They solateral plate; cr2, second layer of chitinous rods; ut, unguitrac- maintain the narrow shape of the folded arolium tor plate. like the cover spine of a book (Roder,€ 1986). While walking on smooth surfaces, the claws diverge and thereby flatten the extensor sclerites, which in is supported by analyses of sequences of a broad turn expand the arolium and thus increase the array of genes (Urban and Cryan, 2007) and in an contact area between the attachment pad and the even more extensive study using seven gene surface (Gladun et al., 2009). It is unlikely that regions (Cryan and Urban, 2012). the dorsal sclerites in the examined Auchenor- However, it was challenged in other studies. A rhyncha have the same function. The bilobed aro- sistergroup relationship between Cicadomorpha lium of Membracoidea probably lacks the potential and Heteropterodea (Heteroptera 1 Coleorrhyncha) to expand, as we did not find a single specimen in appears as a serious alternative to the monophyly which the arolium was visibly inflated. The move- of Auchenorrhyncha. This was suggested in an ment of the dorsal plates in Fulgoridea has been evaluation of combined paleontological, molecular, described in Frantsevich et al. (2008), but their and morphological data (Bourgoin and Campbell, role in everting the terminal part of the arolium is

Journal of Morphology AROLIA IN AUCHENORRHYNCHA 7

Fig. 5. Pretarsus of Philaenus spumarius, interactive 3-dimensional reconstruction. Sclerotized parts blue, membrane covering most of the pretarsus semitransparent, glands green, thickened cuticle of the contact zone pink. Agl, arolium gland; cl, claw; cz, contact zone; dpl, dorsal plate; tar, tarsal segment. uncertain, as the pronation of the claws alone also are dendritic structures (Auchenorrhyncha), stretches the base of the arolium. whereas cross-connections between them occur in Inflation and folding of the arolium appears pos- some species (Euplantulae of Tettigonia, Perez sible in the examined Aphrophoridae. The contact Goodwyn et al., 2006). In Orthoptera, the pads area of the arolium of Philaenus was strongly might function as a damper during jumping and invaginated medially (Fig. 1C), which likely is the landing (Perez Goodwyn et al., 2006). The rods resting position. However, we did not find an stabilize the shape of the pad to prevent strong expanded arolium in any of the specimens at our deformation. A similar function can be assumed disposal. In contrast, the contact area was inflated for Auchenorrhyncha which are almost generally and extended well beyond the claws in specimens characterized by a good jumping capacity (e.g., of Neophilaenus sp., which belong to the same Cercopis vulnerata: Gorb, 2004; P. spumarius: Bur- family. This is apparently not an artifact as this rows, 2006; C. viridis: O’Brien, 2002; Bonsignori condition was also observed in living specimens. et al., 2012: Fulgoromorpha). Interestingly, the However, the position of the dorsolateral sclerites only nonjumping species of our taxon sampling was the same in the deflated and inflated condi- lacks the arolium, which suggests a correlation tion, which clearly suggests that these sclerites between these features. The architecture of the are not involved in inflating the arolium. rods may also help to adapt to irregularities of the substrate surface. A second layer of chitinous rods is described here Thickened Cuticle for the first time. This additional layer is present The cuticle of the contact zone is generally dis- in the investigated members of Cercopoidea and tinctly thickened in insects with arolia (Fulgoro- Membracoidea, but not in Fulgoromorpha. It prob- morpha: Frantsevich et al. 2008; Blattodea: Roth ably is a potential apomorphy of Cicadomorpha. and Willis, 1952; Orthoptera: Slifer, 1950; Manto- phasmatodea: Eberhard et al., 2009; Phasmatodea: Scholz, 2009; Bennemann et al., 2011; Hymenop- Glands tera: Federle et al., 2001). It is usually formed by A gland within the arolium is present in all chitinous rods in different attachment devices examined members of Auchenorrhyncha. A gland (e.g., Beutel and Gorb, 2001) but the arrangement directly located within the arolium has only been of these structural elements varies. Some of them described for Mantophasmatodea (Eberhard et al.,

Journal of Morphology 8 K. FRIEDEMANN AND R.G. BEUTEL 2009). However, it is conceivable that it is more personal observation: several species of Pentato- common than previously thought. In cockroaches momorpha). Therefore, we suggest an extended (Roth and Willis, 1952) and grasshoppers (Slifer, definition of arolium: a lobe between the claws, 1950), gland-like tissue is visible in histological either hollow or filled with gland tissue; virtually sections of the pretarsus, but it was referred to as always with a distinctly thickened cuticle consist- epidermis in these studies. As most cockroaches ing of chitinous rods in the distal part. The aro- leave visible footprints on glass-slides, it is very lium can be distinctly bilobed but the equipment likely that the structures in their arolia indeed with sclerites is homologous to that of single-lobed produce and release secretions. A gland was also arolia. recently described for Tipula (Diptera; Friede- mann et al., in press). Jiao et al. (2000) reported that the secretion in Tettigonia viridissima is ACKNOWLEDGMENTS transported through pore canals of the pad cuticle. However, the canals are only mentioned in the The authors would like to thank Hans Pohl for abstract and there are no images of them in the providing valuable specimens. The authors are article. also indebted to Janin Naumann and Rommy The function of the gland is not entirely clear. Petersohn for providing histological sections of The secretion probably plays a role in adhesion to high quality. The authors would like to thank two smooth surfaces (e.g., Jiao et al., 2000; Orivel anonymous reviewers for their helpful suggestions. et al., 2001). However, in some species of Hyme- The authors declare that there are no known con- noptera, the secretion is not released externally flicts of interest associated with this publication. (Billen, 1986, Jarau et al., 2005), but remains within the pretarsus. A hydraulic function has LITERATURE CITED been proposed by Federle et al. (2001). The liquid of the gland reservoir is pumped into the arolium, Bennemann M, Scholz I, Baumgartner W. 2011. Functional and this results in partial unfolding to increase morphology of the adhesive organs of stick insects (Carausius morosus). Proc SPIE 7975:79751A–79751A-8. the contact surface with the substrate. A hydraulic Beutel RG, Gorb SN. 2001. Ultrastructure of attachment spe- function seems unlikely in the case of Membracoi- cializations of hexapods (Arthropoda): Evolutionary patterns dea, where the lobes of the arolium are not inferred from a revised ordinal phylogeny. J Zoolog Syst Evol extendable. Even though oily footprints were visi- Res 39:177–207. Beutel RG, Gorb SN. 2008. Evolutionary scenarios for unusual ble on glass-slides in all examined members of attachment devices of phasmatodea and mantophasmatodea Auchenorrhyncha, we could not find any canals or (insecta). Syst Entomol 33:501–510. openings. However, this might also be due to fixa- Billen J. 1986. Etude morphologique des glandes tarsales chez tion artifacts and the methods of examination. la guepe^ Polistes annularis (L.) (Vespidae, Polistinae). Actes Presently, the mechanism of the release of glandu- Coll Insectes Soc 3:51–60. Billen J. 2009. Occurrence and structural organization of the lar secretions remains unsolved. In M. seminigra exocrine glands in the legs of ants. Struct Dev 38: (Hymenoptera, Apidae), secretion is produced by 2–15. tendon glands and released at the base of the Bonsignori G, Stefanini C, Scarfogliero U, Mintchev S, Benelli unguitractor plate into a slit between the last tar- G, Dario P. 2012. The green , Cicadella viridis (Hemiptera, Auchenorrhyncha, Cicadellidae) jumps with sal segment and the pretarsus (Jarau et al., 2004). near-constant acceleration. J Exp Biol 216:1270–1279. The secretion contains pheromones which are used Bourgoin T, Campbell BC. 2002. Inferring a phylogeny for hem- for communication in these social insects. How- iptera: Falling into the ‘Autapomorphic Trap’. Denisia 4:67– ever, as the glands we observed are not homolo- 82. gous with the tendon glands this mechanism can Brown BV. 1993. A further chemical alternative to critical- point-drying for preparing small (or large) flies. Fly times 11: be excluded for Auchenorrhyncha with reasonable 10. certainty. Burrows M. 2006. Jumping performance of insects. In conclusion, we can say that the traditional J Exp Biol 209:4607–4621. definition of an arolium as a single hollow lobe Butler CG, Gletscher DJC, Walter D. 1969. Nest entrance marking with pheromones by the honeybee Apis mellifera L. between the claws (Dashman, 1953) is not always and by a wasp, Vespula vulgaris. Anim Behav 17:142–147. applicable. In fact, in most cases they are not hol- Cryan JR, Urban JM. 2012. Higher-level phylogeny of the low but filled with gland tissue. 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