Thoracic scent efferent system and exponium of Aphylidae (Hemiptera: Heteroptera: Pentatomoidea), its architecture and function

The external morphology of Aphylidae was studied previously in detail by the two junior authors, including the description of unique derived structures formed by their lateral thoracico-abdominal region (the exponium). Here we provide an additional description of the external scent efferent system of the metathoracic scent glands of species in the genus Aphylum Bergroth, 1906 (based on scanning electron microscope study) and its connection with an autapomorphic aphylid thoracico-abdominal region, the exponium. The origins of exponial sclerites are discussed and function of the exponium is hypothesised as being part of a complex defensive mechanism in the Aphylidae.


INTRODUCTION
The insect clade Heteroptera is explicitly characterized by autapomorphic pattern of repellent scent glands (Schuh & Slater, 1995;Weirauch, 2006a, b), the dorsal abdominal scent glands in the larvae, often persistent in adults (summarized by Weirauch, 2006b), and the metathoracic scent glands (= MTGs) in the adults (at least in Neoheteroptera).The names of glands clearly express their usual somatic position.The primary functions of the metathoracic scent gland secretion are repugnatorial and defensive; bactericid, fungicid or pheromonal functions are probably secondary.The external scent efferent system (see terminology in Material and Methods) serves for rapid ejection and evaporation of the repellent secretion and simultaneously for protection of the specimen against toxicity of its own secretion (for chemism see, e.g., Staddon, 1979Staddon, , 1986;;Aldrich, 1988).The external scent efferent system of the metathoracic scent glands in the adult Pentatomomorpha, particularly the Pentatomoidea, has been recently studied in detail by Kment & Vilímová (2010a, b).
The Aphylidae is a small clade of Pentatomoidea endemic to Australia, including only two genera and three described species: Aphylum Bergroth, 1906with A. syntheticum Bergroth, 1906 (New South Wales, South Australia, Victoria) and A. bergrothi Schouteden, 1906 ("Australia"), and Neoaphylum Štys & Davidová-Vilímová, 2001 with N. grossi Štys & Davidová-Vilímová, 2001 (Western Australia) (Cassis & Gross, 2002).Štys & Davidová-Vilímová (2001) provided a detailed diagnostic description and discussion of some aspects of the external morphology of both Aphylum and Neoaphylum, especially the modified lateral parts of thorax and abdomen that form an exponium.The new term "exponium" was derived from the Latin verb exponere (= to expose, to exhibit) by adding termination -ium, thus forming a neuter noun.It was coined to refer to a group of three (Aphylum) or four (Neoaphylum) sclerites (called "exponial sclerites" and indicated by acronymic abbreviations) freely visible in dorsolateral view.The exponium is situated in a space delimited by the pronotum (anteriorly), resting forewing (mesally) and dorsal abdominal laterotergites (posteriorly; in Neoaphylum also by dorsally shifted ventral abdominal laterotergites); lateral margin of the exponium is free.For details and terminology see Table 1.Presence of the exponium is a diagnostic autapomorphy of the Aphylidae, and it has been noticed by all the authors ever concerned with this taxon, but not named and not precisely homologized prior to Štys & Davidová-Vilímová (2001).Štys & Davidová-Vilímová (2001) showed that exponium is formed by transformed lateral elements of thorax and abdominal basis, which are closely associated and externally exposed.The exponium was then regarded as of unknown function.The authors also described part of the external scent efferent system of the metathoracic scent glands, not paying any attention to the microsculpture.
Herein we are concerned with a detailed examination of the external scent efferent system in the Aphylidae using scanning electron microscope, particularly in elucidation of the architecture and possible function of the exponium -a structure that is closely associated with and forms a part of the external scent efferent system, and hypothesise the possible function of this unique formation.Admittedly, we do not possess any observation (the less any experimental evidence) of the actual function of the struc-tures concerned in live individuals -we can only generalize from situations known in other Heteroptera.However, we prefer to provide a viable and potentially heuristically stimulating hypothesis rather than become limited by a mere description.

MATERIAL AND METHODS
The following specimens were examined: "Aphylum sp.1 cf.bergrothi": &, Australia, Queensland, Clermont, viii.Line drawings of thoracic pleuron were made using stereomicroscope with an attached camera lucida.Scanning electron microscope (SEM) micrographs were prepared in the Laboratory of Electron Microscopy, Biological Section, Faculty of Sciences, Charles University in Prague, using JEOL 6380 LV SEM.Prior to SEM examination, the specimen was coated with gold.Kment & Vilímová (2010a, b) recently defined the basic terms related to the MTG and associated structures: The metathoracic scent apparatus consists of internal parts, and the thoracic scent efferent system, further differentiated into internal (internal orifice and vestibule) and external parts.The external scent efferent system consists of ostiole, peritreme, and evapora-torium.The terminology follows these authors for the external scent efferent system, and Štys & Davidová-Vilímová (2001) for the other thoracic structures.For terminology related to the exponial sclerites see Table 1 and Figs 1-4.Our (re)description of the exponium differs in several points from that by Štys & Davidová-Vilímová (2001), but it would be overly pedantic to enumerate all the points of difference; the present text should be regarded as authoritative.The Figs 1-4 have been taken from Štys & Davidová-Vilímová (2001: Figs 13-16) with only part of the lettering altered.
Anterior mesal exponial sclerite (AMES) is located most anteriorly, situated between pronotum (anterior edge of AMES loosely fitting the sublateral indentation of the posterior margin of pronotum), proximal part of the costal margin of resting forewing (see below) and LES.It is of an approximately trapezoid outline, its lateral margin bends ventrad and mesad toward the ventral surface of a nearly horizontal mesepimeron, the lateral margin medially provided with a Y-shaped incision making AMES more or less bipartite.The incision is forming the lateral end of evaporatory channel -an impressed groove leading towards the lateral margin of metathoracic spiracle.Surface of AMES is slightly rumpled, its ventral part bearing mycoid microsculpture (Fig. 12) gradually merging with lightly punctured sculpture of its dorsal part contacting forewings  Continuous with metepisternum, its lateral margin forming a part of lateral body margin; subdivided into a dorsal area and a lateral, subvertical area (= "modified lateral part of LES"), the latter being overlapped by the pronotum and bipartite (Aphylum), or fitting its margin and entire (Neoaphylum); mesal margin covered by forewing and forming anterior part of forewing groove jointly with abdominal mediotergites 1 and 2. LES Lateral exponial sclerite Neoaphylum (Fig. 4) Dorsally reflected part of mesepimeron.
Interspaced between AMES and LES sharing with them the same gross sculpturation; it is a flap-like projection situated just above the mesepimeron cephalad the metathoracic spiracle.Situated above the mesepisternum and associated with hindwing articulation and medio-tergites 1 and 2 basis, always lacking the puncturation of LES and TES, and always subdivided in two parts.Its mesal region covered by forewings (accommodating the hypocostal lamina), anterior margin contacting the pronotum, lateral and posterior margins either engulfed by LES (Aphylum), or the lateral one free and the posterior one contacting PMES (Neoaphylum).With mycoid microsculpture.minating caudally in a deep fovea.The groove serves for holding the exceedingly short hypocostal lamina of forewing and the fovea accommodates its abrupt denticleshaped termination, functioning obviously as a dorsally shifted druck-knopf mechanism.The part of AMES covered dorsally by forewing contacts mesally the articulatory apparatus of hindwing and fused abdominal mediotergites 1 and 2.

AMES
Lateral exponial sclerite (LES) is the largest of the exponial sclerites, situated slightly obliquely between pronotum, resting forewings and TES, of oblong outline with a posterodorsal projection towards the costal margin of forewing and a wide topographically postero-ventral lobe identical with metepisternum.LES exceeds pronotum ventrally (Figs 7,9).LES is almost flat, with puncturation (Figs 9-10) roughly identical with that on all the dorsum and lateral parts of the body and TES (Fig. 8).Punctures are sparser dorso-posteriorly than on rest of sclerite surface (Fig. 9).Lateral margin of dorsum of LES is sharply defined and forming a boundary between LES proper (metapostnotal origin) and metepisternum.
Triangular exponial sclerite (TES) is named after its triangular outline, with apex pointing ventrally, located between LES, resting forewings and dorsal abdominal laterotergite 3 (Figs 7-9).TES is almost flat, with puncturation, roughly identical with those on all the dorsum, lateral parts of body and LES (Fig. 9).
Mesal margins of LES and TES are covered by costal margin of resting forewing (distal to termination of hypocostal lamina) and forming lateral part of forewing groove (its mesal part being formed by lateral margin of fused abdominal mediotergites 1 and 2).
There is a space between the ventrally expanded lateral parts of pronotum and the exponium, the pronotalexponial gap (7)(8)(9)4,(14)(15)17: peg).In Aphylum spp., the gap is enclosed by lateral expansion of the pronotum, ventral margin of AMES and anterior margin of LES.The internal portion of the pronotalexponial gap in Aphylum forms a nearly closed pronotalexponial tunnel between the ventral margin of AMES and the postero-median margin of pronotum in lateral view , and posterior margin of pronotum, lateral margin of mesepimeron and anterior margin of metepisternum in ventral view .The remaining lateral portion of the pronotal-exponial gap is obscured in lateral view by the posterior pronotal margin overlapping the anterior margin of LES but could be seen in ventral view (Figs 14,17: peg), its width depending on the adduction / retraction of pronotum towards pterothorax.
The pronotal-exponial tunnel appears as an elongate rectangular opening in lateral view  or triangular opening in ventral view (Figs 14-19: pet) and allows passing of the metathoracic scent gland secretion from ventral to lateral external surface of the body.

Taxonomy
We are aware of the cladistic opinion by Grazia et al. ( 2008) on a sister-group relationship between the Cyrtocoridae and (Aphylidae and Pentatomidae s. str.).However, we retain the family level ranking of the two former groups preferring at the moment the analytical approach to classification of the high level pentatomoid clades.[For a possible sister-group relationship between the Cyrtocoridae (Neotropical) and Aphylidae (Australian) see Davidová-Vilímová & Štys (1994) and Štys & Davidová-Vilímová (2001).]The previous taxonomic history of the Aphylidae was summarized by Štys & Davidová-Vilímová (2001) and Cassis & Gross (2002).
The present knowledge of species-level taxonomy of Aphylum does not allow even a reliable identification of the two species established by Bergroth (1906) and Schouteden (1906a); prior to a revision we cannot rely on any previous species-level data.The diagnostic characters used by Schouteden (1906b) are plastic and more than two species of males are present in material of Aphylum available to us (P.Štys, unpubl.).We have seen several specimens identified as A. bergrothi from Queensland and several as A. syntheticum from various parts of Australia.However, for the above reasons we do not consider their identification reliable, and call the two specimens examined in this paper "A.sp. 1 cf.bergrothi" and "A.sp.2", respectively (see Material and Methods), and the specimen of Aphylum studied by Štys & Davidová-Vilímová (2001) "A.sp. 3 cf.syntheticum".

Morphology of the external scent efferent system
The external scent efferent system of Aphylum is well developed, including a long, laterally prolonged peritreme, and a very large evaporatorium covering most of the metapleuron and the mesepimeron.Such a situation is not uncommon among the Pentatomoidea (cf.Kment & Vilímová, 2010a).However, there are some features that ought to be emphasized: (i) The vestibular scar is missing.Despite the vestibule of the Pentatomoidea being completely closed, the narrow line of a scar-like appearance remains externally visible in place of adhesion of the scent groove margins in several taxa.This scar starts at the anteromedian margin of metacoxal cavity and continues laterally towards the proximal margin of ostiole (Kment & Vilímová, 2010a, b).The vestibular scar occurs regularly in the Coreoidea, Lygaeoidea, Pyrrhocoroidea, as well as in several families of the Pentatomoidea, i.e., Thaumastellidae, Cydnidae, Thyreocoridae, Parastrachiidae, Phloeidae: Phloeinae, Plataspidae, and Dinidoridae (partim) (e.g.Brindley, 1934;Remold, 1962Remold, , 1963;;Štys, 1967;Lis, 1994; summary in Kment & Vilímová, 2010a, b).
(ii) Peritreme reaching lateral margin of metapleuron (metepisternum) and merging with the surface of ventral margin of LES.This is a unique feature of Aphylum, as we have never seen another species of the Pentatomomorpha (P.Kment & J. Vilímová, pers. observ.)with so extremely prolonged peritreme merging apically with the lateral margin of metapleuron.Moreover, this character is not shared with Neoaphylum grossi, in which the peritremal apex reaches only to ca. 3/4 of metapleuron width and is gradually fading off apically (cf.Štys & Davidová-Vilímová, 2001: Fig. 12).The whole peritreme in Aphylum is distinctly elevated above the surrounding thoracic surface, therefore the secretion could easily pass from the peritremal surface to the surrounding cuticle before reaching the lateral end of peritreme; this seems strange considering that peritreme should serve to spread and direct the secretion flow.Without detailed knowledge of how the mechanisms of ejection and spreading the scent gland secretion work in Aphylum we cannot explain the function of its peritreme.The elevation of the peritreme above metepisternal surface is characteristic of Neoaphylum as well, although its peritreme is much shorter.
(iii) Evaporatorium reaching lateral margin of mesepimeron and metepisternum, and continuing as far laterad as ventral surface of AMES.The evaporatorium widely extended and reaching the lateral thoracic margins of both meso-and metapleuron is rather rare among Pentatomoidea but could be found e.g. in Plataspidae, Phloeidae: Serbaninae, some Cydnidae (Amnestus Dallas, 1851) (Kment, 2009;Kment & Vilímová, 2010a).However, the mycoid surface reaching the external lateral surface of the body (here on ventral surface of AMES) is a unique character of the Aphylidae, being closely connected with the apomorphic structure of the thorax and development of the exponium (see below).This extension of the evaporatorium up to the ventral surface of AMES is further assisted by the development of evaporatory channel in Aphylum*.The term evaporatory channel was defined by Kment & Vilímová (2010a) as a depressed channel covered with mycoid surface conducting the secretion from the peritreme towards the lateral pleural margin.The evaporatory channel of Aphylum does not fit the definition in full, as it does not start in proximity of the peritreme apex, but at the end of metathoracic spiracle.However, the close association of evaporatory channel with metathoracic spiracle is not unique, occurring also in Triplatyx Horváth, 1904 (Pentatomidae: Pentatominae) (Kment, 2008, as "outlet channel") or in the Aradidae (Usinger & Matsuda, 1959;Larivière & Larochelle, 2006).
(iv) The close association of the metathoracic spiracle with the evaporatorium and the external scent efferent system in general (most pronounced e.g. in Tessaratomidae: Tessaratomini) suggests that metathoracic spiracles participate in the defensive process by promoting dispersion of the secretion by means of an exhalation-ventilation process (Carver, 1990;Kment & Vilímová, 2010b).The detailed studies of this hypothesis, particularly the mechanism of scent excretion, still remain to be conducted.
(v) Pattern of the microsculpture of evaporatorium in Aphylum is frequent in Heteroptera, distinctly extending the surface of this area.However, the detailed pattern of mycoid microsculpture of Aphylum is somewhat different from that known in most of the other Heteroptera studied.The caps are quite low and close each to other, connecting bridges are low, the surface of alveoles is almost smooth with only sporadic and inconspicuous trabeculae.The more common heteropteran situation is represented by high caps and high bridges, caps being farther apart allowing thus for larger alveoles, with many high and undulating trabeculae (e.g.Carayon, 1971;Carver, 1990;Kment, 2009;Kment & Vilímová, 2010a, b).However, we cannot exclude that the absence of trabeculae is only virtual, being caused by an insoluble enamel-like crust covering the mycoid microsculpture -a not unusual condition in the Pentatomoidea.
The evaluation of the detailed differences in mycoid miscrosculpture among different heteropteran species is problematic, considering (i) artifacts of SEM micrographs due to uneven surface of evaporatorium (the gyrification) or contamination of the examined surface, (ii) variability of mycoid surface among different parts of evaporatorium even of the same specimen (cf.Kment & Vilímová, 2010a: Figs 110 and 111), (iii) limited number of pentatomoidean species with mycoid microsculpture examined under SEM (for references see Kment & Vilímová, 2010a, b) which is a crucial impediment in determination of plesiomorphic, apomorphic and homoplasious patterns, attempted previously only by Hasan & Kitching (1993) in a very limited sample of species.The scarce data about this feature do not allow any general suggestion or explanation, we only can conclude that the Aphylum pattern is rather rare.
Štys & Davidová-Vilímová ( 2001) regarded the homology of AMES and posterior mesal exponial sclerite (PMES) as uncertain, however, they suggested possible origin of AMES from modified mesopleural articulation of forewing.The recent SEM investigation and the discovery of mycoid microsculpture on AMES support origin of this sclerite from dorsal part of metapleuron 276 * Neoaphylum grossi is known from a holotype only (Fig. 34), and, consequently, some of the following observations are tentative and could not have been confirmed by SEM study.The metathoracic spiracle is extremely long, terminating laterally at the midlength of the "modified lateral part of LES" (Štys & Davidová-Vilímová, 2001: Figs 12, 14).The thoracic sternal and pleural parts are rather brilliant but, nevertheless, the extent of evaporatorium (presumably with mycoid microsculpture) can be estimated owing to degree of lustre (or the lack of it) and appearance of cuticle, as follows: mesepimeron up to its lateral margin; metepisternum up to its lateral margin (probably); "modified lateral part of LES"; AMES; the most lateroventral articulatory sclerite of forewing (in resting position = the most anterior sclerite in spread forewing).The apparent spread of metathoracic gland secretion onto forewing articulatory system in N. grossi does not seem to have a parallel among Pentatomomorpha, and is shared by the Dipsocoridae and probably Stemmocryptidae (both Dipsocoromorpha s. str.-P.Štys, unpubl.)only.
The PMES of Neoaphylum is formed from a dorsally turned part of mesepisternum (Štys & Davidová--Vilímová, 2001).Mesal parts of Neoaphylum AMES and PMES are covered by forewings and accommodates the hypocostal lamina that terminates just at the boundary between PMES and LES.Such a situation could suggest homology of PMES with the posterior part of AMES in Aphylum rather than with mesal part of LES as suggested elsewhere and based on ventral association of PMES.The costal margin of forewing also covers the mesal margins of LES and TES that probably form part of the forewing groove (per analogy with Aphylum).
Štys & Davidová-Vilímová ( 2001) hypothesised that LES is of a metepisternal-metapostnotal origin.The metapleural origin of the sclerite is supported by the peritreme ending on ventral face of LES, as the location of peritreme is in general restricted to metathorax (Kment & Vilímová, 2010a).Unlike in AMES, the mycoid microsculpture does not continue from the metapleural evaporatorium on LES surface, therefore the sclerite most probably has no role in delivery of the scent secretion.
Despite the three (or four) principal exponial sclerites described in detail previously (Štys & Davidová-Vilímová, 2001), we recognize here another functional element in the highly apomorphic structure of aphylid thorax, the pronotal-exponial gap, leaving free space between the posterior margin of the laterally explanate pronotum and anterior margin of the exponium.In Neoaphylum grossi, the pronotum is not closely attached to LES, the pronotal-exponial gap is opened in its entire length, being slightly scimitar-shaped, beginning at the ventral margin of AMES and slightly widening laterally* (Fig. 4: peg) (Štys & Davidová-Vilímová, 2001).In species of Aphylum the pronotal-exponial gap is laterally reduced by posterior pronotal margin overlapping over anterior margin of LES, being apparent only in its basal part and appearing as a narrow opening between AMES and pronotum (the pronotal-exponial tunnel).The pronotal-exponial gap or tunnel represents the only interruption of the otherwise homogenous "bonnet" of laterally expanded parts of pronotum, exponium and abdominal laterotergites covering and protecting the ventral side of the body when the bug is closely attached to substrate.

Potential function of apomorphic thoracic structures of Aphylidae
The Aphylidae are rather hemispherical bugs of armoured appearance owing to the hypertrophied mesoscutellum covering most of the posterior parts of dorsum and to the expanded lateral region of both the thorax (pro-notum, exponium) and abdomen (laterotergites) protecting the venter .Ejection of the pungent secretion of the metathoracic scent glands is the common defensive reaction in Heteroptera (e.g.Remold, 1962Remold, , 1963;;Staddon, 1986).However, the wide and flattened body venter and especially the ventrally expanded lateral margins in Aphylidae would prevent effective spreading of the secretion laterally towards a potential predator.The thorax of the Aphylidae has been uniquely transformed: its dorsal thoracic margins have been expanded ventrad allowing for a complete coverage of venter of the body when resting on substrate, and retaining at the same time the possibility of chemical defence by metathoracic scent glands.The modified structures of the lateroventral thoracic parts (mesopleuron reflected dorsad and extending as AMES or AMES + PMES onto the external suface of the resting body), jointly with the modified external scent efferent system (evaporatory channel, mycoid microsculpture extending onto AMES) and the pronotalexponial gap/tunnel, form a free passage for the scent secretion.It may spread from the ventrally situated ostiole to lateral external surface of the body.The autapomorphic structure of the thorax in Aphylidae probably represents a compromise allowing a coexistence of two different but complementary mechanisms of defence.
The thoracic structure of Aphylidae, including the autapomorphic exponium, is so unique that comparison with other Heteroptera is problematic.Hemispherical bugs with body shape similar to Aphylidae are not rare, such body shape is among the Pentatomomorpha characteristic of the pentatomoid families Lestoniidae (Australian), Canopidae, Megarididae (both Neotropical), Plataspidae (Old World), and occurs also in the Scutelleridae (e.g., Sphaerocorini) and Pentatomidae (e.g., some Discocephalinae).Undoubtedly, the strongly sclerotized and strongly convex body with nearly flat to concave venter provides a strong mechanical protection against small predators (like ants) and ovipositing parasitoids.However, the mechanical protection can hardly replace the chemical antipredatory mechanisms, if larger active predators (like insectivorous birds, small mammals, lizards and geckos) are involved.This is also suggested by the diverse architecture of the external scent efferent system in those Pentatomoidea provided with a wide and flat ventral side of the body.We can identify several modifications of how the external scent efferent system changes in relation to the problem of effectively spreading scent secretion.
First, the external scent efferent system may have been reduced to a different degree, occasionally resulting in complete reduction of the metathoracic scent glands (some Scutelleridae - Kment, 2009).Such bugs must relay on mechanical protection apparently sufficient for coping with their natural enemies.Among bugs with hemispherical body, such a situation exists in Megarididae with minute ostiole only and complete reduction of peritreme and evaporatorium (see McAtee & Malloch, 1928;McDonald, 1979).In Lestoniidae, the ventral surface of the body is flat and meso-and metathorax are laterally covered by explanate lateral margins of pronotum and costal area of hemelytron (China, 1955;McDonald, 1969), a situation resembling that of the Aphylidae.However unlike them, Lestoniidae also show a remarkable reduction of the external scent efferent system, which moreover differs considerably between the two included species (peritreme and small evaporatorium developed in Lestonia grossi McDonald, 1969versus peritreme and evaporatorium missing in L. haustorifera China, 1955) (McDonald, 1969;Kment, 2009).
The second possible method is exemplified by a well developed external scent efferent system with tendency of its particular components to shift (usually the ostiole), prolong (usually the peritreme) or extend (usually the evaporatorium) towards lateral body margin.Such a trend is evident in most Plataspidae, in which (a) the ostiole is shifted laterad to ca. half-width or one-third of metapleuron, (b) the peritreme (sometimes prolonged) reaches near the lateral margin of metapleuron; (c) an analogous pseudoperitremal structure has evolved in posterolateral angle of mesopleuron, and (d) the evaporatorium is extended, covering almost entire thoracic venter (Kment, 2009;Kment & Vilímová, 2010a, b).
In the Canopidae, the situation combines the two methods -the peritreme is considerably reduced, but evaporatorium is in some species extended laterally and reaches the lateral margin of mesopleuron (McAtee & Malloch, 1928;Kment, 2009).Both the methods, either reduction of the external scent efferent system (and thus the chemical defence) or its remarkable development with lateral shift of its particular components, can be observed also in Aradidae remarkable for their very flat body (cf.Usinger & Matsuda, 1959;Larivière & Larochelle, 2006).
Unfortunately, nearly nothing is known about the biology of Aphylidae.Cassis & Gross (2002) classified all the three known species of Aphylidae as arboreal, herbivore, terrestrial and volant.Gross (1975) mentioned that "both [Aphylum] species certainly pass a great deal of their time under Eucalyptus bark".The specimens of Aphylum syntethicum were collected under bark of Eucalyptus camaldulensis Dehnh.(Myrtaceae); at first sight they could easily be mistaken for beetles of the genus Paropsis Jenyns, 1841 (Chrysomelidae: Chrysomelinae) which are also common under the bark of Eucalyptus spp.(Gross, 1975).The behaviour of Aphylidae is unknown and we do not know what predators may endanger them.The obvious ones, ants and spiders, live in the same habitat that is also easily accessible to adults of hymenopteran parasitoids (P.Štys, pers.observ. of the microhabitat).
Moreover, there is also no evidence of Aphylidae having or lacking parental care, various kinds of which are widespread in Pentatomoidea (Cydnidae, Parastrachiidae, Phloeidae, Tessaratomidae, Acanthosomatidae, Scutelleridae, Dinidoridae, Pentatomidae) (summary in Tallamy & Schaefer, 1997).If parental care indeed exists in the Aphylidae, their specialized scent efferent system and related defensive strategies may have an essential role in guarding the eggs and/or young larvae, especially when hidden under the parent's body.