Eur. J. Entomol. 103: 97–108, 2006 ISSN 1210-5759 Metathoracic glands and associated evaporatory structures in Reduvioidea (Heteroptera: Cimicomorpha), with observation on the mode of function of the metacoxal comb CHRISTIANE WEIRAUCH American Museum of Natural History, Division of Invertebrate Zoology, Central Park West at 79th Street, New York, NY 10024, USA; e-mail: [email protected] Key words. Heteroptera, Reduviidae, metathoracic gland, morphology, defensive gland, dissemination of secretion Abstract. Structures that assist in spreading secretions produced by the metathoracic glands were examined in Reduviidae and Pachynomidae (Heteroptera). The systematic distribution of a row of long and stout setae on the metacoxa, the metacoxal comb, was reinvestigated in a representative sample in both taxa. Observations on living Dipetalogaster maximus (Reduviidae: Triatominae) corroborated the interpretation of this metacoxal comb as an evaporatory device, which assists in atomizing the gland secretions. In addition to the metacoxal comb, a row of stout setae on the metacetabulum – a metacetabular comb – was found in several Reduvii- dae, which interacts with the metacoxal comb during rotation of the metacoxa. In addition to those atomizing devices, cuticular modifications surrounding the opening of the metathoracic gland, which presumably form evaporatoria, were discovered in Ectricho- diinae. The meshwork-like structure of this cuticle resembles the cuticular modifications found associated with the opening of the Brindley’s gland in Reduviidae, but differs from the mushroom-like evaporatoria around the metathoracic glands in most Cimi- comorpha and Pentatomomorpha. Thus, two fundamentally different mechanisms to spread secretions of the metathoracic gland – atomization and evaporation – are present in Reduviidae. INTRODUCTION located metathoracic Brindley’s gland (Brindley, 1930; A complex gland system in the metathorax of the adult Carayon, 1962). is one of the diagnostic and apomorphic features of Het- As to external disseminating devices associated with eroptera (Carver et al., 1991). Apart from functioning e.g. the metathoracic glands, Reduvioidea do not possess a in intraspecific aggregation and mating behavior, the well-defined scent gland groove (Carayon, 1971; secretions of this gland are defensive (Staddon, 1979, Staddon, 1979), which caused Schuh & Štys (1991) to 1986). In the majority of Cimicomorpha and Pentatomo- conclude that its reduction is an apomorphic feature of the morpha the metathoracic glands are well developed, open group. Furthermore, peritreme and evaporatory areas with through paired orifices laterally or ventrolaterally on the mushroom-like cuticle appear to be absent in both taxa. metepisternum (Carayon, 1971; Cobben, 1978), and the Nevertheless, Reduvioidea possess structures that seem to metepisternum is equipped with structures that are be involved in the dispersion of scent gland secretions. involved in the spreading of the gland secretions. In many Davis (1961) described a “row of bristles forming a comb Pentatomomorpha and Cimicomorpha these last struc- located basally on the anterior lateral surface of each hind tures comprise a scent gland groove (“gouttière odori- coxa” in several taxa of Reduviidae, and referred to this fique” of Carayon, 1971), a peritreme, and in addition assemblage of setae as “hind coxal combs”. When semi- evaporatoria usually with mushroom-like sculpture rotating the hind coxa – for example during walking – (Johansson, 1957; Remold, 1962, 1963; Filshie & Water- those bristles move over the margin of the coxal cavity house, 1969; Johansson & Bråten, 1970; Carayon, 1971; and brush over the opening of the metathoracic gland. Staddon, 1979; see also Fig. 22). Davis (1961) assumed that the comb disseminated the The cimicomorphan group Reduvioidea comprises the gland secretions, an opinion reiterated by Schofield & small taxon Pachynomidae – 2 subfamilies with 4 genera Upton (1978). (Carayon & Villiers, 1968) – and the speciose and mor- No other structures that might assist in spreading the phologically diverse Reduviidae with over 20 recognized metathoracic gland secretions have been described in subfamilies in more than 900 genera (Maldonado, 1990). Reduviidae and Pachynomidae. In this paper, the exami- Metathoracic glands are documented for numerous taxa in nation of structures associated with the opening of the Reduvioidea, even though they seem to be consistently metathoracic gland aims to expand the knowledge on absent in certain groups (Carayon, 1962; Cobben, 1978). such structures in Reduvioidea. In a first step, structure The apparent reduction of the metathoracic gland in and location of the metathoracic gland were re-examined Reduviidae compared to other cimicomorphan and to in Panstrongylus herreri (Triatominae). Then 71 species many pentatomomorphan groups (Carayon, 1971; Cob- of Pachynomidae and Reduviidae were dissected, macer- ben, 1978) has given rise to speculation concerning their ated, and examined light microscopically to establish function in relation to the often well developed, dorsally absence or presence of the metathoracic gland. A larger 97 taxon sample comprising 152 species, was used for light metacetabular callus; metdep – metacetabular depression; mucut microscopical search for external evaporatoria. Scanning – mushroom-like cuticle; om – opener muscle of metathoracic electron microscopical investigations on a more limited gland; oma – apodeme of opener muscle of metathoracic gland. sample supplemented these results. The metacoxal comb Material examined. The specimens examined for this project belong either to the American Museum of Natural History was re-examined in 152 species of Pachynomidae and (AMNH), New York, the “Museum für Naturkunde, Zentralin- Reduviidae to refine the picture of its systematic occur- stitut der Humboldt-Universität” (ZMHB), Berlin, Germany, the rence. Observations on living specimens of Dipetalo- Muséum National d’Histoire Naturelle, Paris (MNHN), the gaster maximus (Reduviidae, Triatominae) aimed to Insect Collection of the “Universidade Federal do Rio Grande demonstrate the function of the metacoxal comb. The do Sul” (UFRG), Porto Alegre, Brazil, or were donated to the region surrounding the gland opening was examined for author by J.-M. Bérenger, D. Mahsberg, S. Roth, W. Sudhaus, structures that might be involved in the dissemination of S. Trenner, E. Wachmann, and A. Zwick. Living specimens of gland products. For comparative purposes, the area sur- Dipetalogaster maximus were kindly provided by G. Nentwig rounding Brindley’s gland opening was examined and (Bayer AG, Leverkusen). illustrated for several representatives of Reduviidae. The method(s) of observation for each taxon is given below, with external light microscopical examination for opening of the MATERIAL AND METHODS metathoracic gland, mushroom-like cuticle, metacoxal comb and metacetabular comb only (°), additional internal examina- Light and scanning electron microscopical observation of tion for the metathoracic gland (^), and additional scanning the metathoracic gland and associated structures. Alcohol electron microscopy (ª) are listed in Table 1. preserved specimens of Panstrongylus herreri Wygodzinsky PACHYNOMIDAE: Aphelonotinae: Aphelonotus sp.°, Peru were dissected and structures associated with the metathoracic (AMNH); Pachynominae: Camarochilus sp.° (AMNH), gland illustrated using a NIKON SMZ1500 stereomicroscope *Pachynomus picipes Klug^, (ZMHB); Punctius alutaceus with camera lucida equipment. For more detailed observation, (Stal)°, South India (AMNH). the gland and attached structures were transferred to a slide and REDUVIIDAE: Centrocneminae: Centrocnemis sp.°, examined and illustrated using a Nikon Eclipse 80i compound Bouthan (AMNH), *Neocentrocnemis sp.° (ZMHB); Cetheri- microscope with camera lucida. Dried or alcohol preserved nae: Caprocethera cave Breddin° (ZMHB), *Carcinomma sp.°, specimens were used for dissection and internal observation of Ghana (AMNH), *Cethera musiva (Germar)^, Cetheromma the metathoracic gland in other taxa. telescopus Jeannel° (ZMHB), *Eupheno pallens (Laporte) ª, For external observation only, the metathorax surrounding the Chryxinae: Chryxus sp.°, Panama (AMNH); Ectrichodiinae: opening of the metathoracic gland, the metacoxal comb and the Afrocastra sp.°, Congo (AMNH), Antipula sp.°, Sri Lanka metacetabular comb in the remaining species of Reduviidae and (AMNH), Bayerus sp.°, South India (AMNH), *Brontostoma in Pachynomidae were examined in dried or alcohol preserved colossus (Distant)^, B. discus (Burmeister)° (AMHH), Cen- specimens using either the NIKON SMZ1500 or a WILD traspis insignis Schouteden° (AMHH), Cimbus sp.°, Phillipines HEERBRUGG 307800 stereomicroscope. Light microscopical (AMNH), Cleptria sp.°, Congo (AMNH), Cricetopareis tucu- observation allowed for assessment of shape and depth of the mana (Berg)° (AMNH), Daraxa nigripes Stål° (AMNH), depression in Ectrichodiinae, as well as identification of modi- *Ectrichodia crux Thunberg^, Ectrichodia sp.°, Congo fied cuticle (rough surface versus very smooth integument on (AMNH), Ectrichodiella minima (Valdés)° (AMNH), the remaining pleuron). The exact structure of this modified Ectrychotes andeae (Thunberg)° (AMNH), Glymmatophora cuticle (meshwork-like or not) however can only be recognized erythrodera (Schaum)° (AMNH), Guionius sp.°, South India through use of the scanning electron microscope. For scanning (AMNH), Haematorrhophus pedestris