Morphology, arrangement and classification of sensilla on the apical segment of labium in Peiratinae (Hemiptera: Heteroptera: Reduviidae)

Abstract

The present paper describes sensory structures on the apical segment of the labium in representatives of the subfamily Peiratinae (Heteroptera: Reduviidae), using the scanning electron microscope. The study is based on dry material representing 19 species and 16 genera. Within Peiratinae thirteen morphologically distinct types of sensilla were identified. Among them were four new types of sensilla (porous placodea sensillum [PPLS], multilobate sensillum [MS], domeelongated sensillum [UDES], and pit peg sensillum type 2 [NPPS2]) were found. Mechanosensilla are evenly distributed on the surface of the labium and form a characteristic pattern in various species. The main characters of the third visible (apical) segment of the labium are: presence of different sized sensilla of the chaetica type 1, 2, and 3; trichodea sensilla (TS); campaniform sensilla (CS); and various types of nonporous pit peg sensilla (NPPS1, NPPS2, and NPPS3). Distally on the apical segment of the labium dome-elongated sensilla (UDES) there are a characteristic arrangements, described as (3+3) and (1+2). Chemical sensilla are grouped on the tip of the labium. The position, number, and types of chemical sensilla on this area are very similar in all studied species.

Comparative Analysis and Systematic Mapping of the Labial Sensilla in the Nepomorpha (Heteroptera: Insecta)

“…Consequently, for nepomorphan taxa the five patterns of the distribution of the labial tip sensilla can be presented (above). In comparison with the other heteropteran infraorders it has been observed that the morphology and distribution of the labial tip sensilla in the Nepomorpha are distinctly varied with respect to what has been reported in the Gerromorpha (Brożek and Zettel, in prep), Pentatomomorpha [19, 21], and Cimicomorpha: Reduviidae [15, 25]. In terms of diversity and abundance of the sensory system on the labial tip, the Nepomorpha come second to the Gerromorpha.…”

“…An undifferentiated sensory system occurs in the Pentatomomorpha (e.g., Dysdercus fulvoniger and D. koenigii , D. fasciatus, D. intermedius, Lygus lineolaris, and Neomegalotomus parvus ), where the labium tip usually represents one morphological type of basiconic sensilla functioning as the contact-chemoreceptive sensilla (several pairs), basiconic gustative sensilla (several pairs), and basiconic olfactive sensilla (one or two pairs) [17, 19, 21, 22, 37]. In some of the Reduviidae one type of peg and peg-in-pit sensilla have been noticed [15, 25, 38]. Furthermore, two types of mechanosensilla (small hairs and long bristles) have been identified on the tip of the labium by Bernard [39].…”

“…Such information is also used for the interpretation of newly described labial sensilla such as clubbed-like sensillum (CBS), paddle-like sensillum (PDS), cupola-like sensillum (CUS), finger-like sensillum (FRS), freniale-like sensillum (HLS), chaetic sensillum with a divided tip (CHD), star-like sensillum (STS), and multilobed sensillum (MPS). The remaining types of sensilla mentioned in the present paper (Table 1) are known from previous descriptions of other authors [4, 6–8, 15, 24]. Table 1 includes information about functional and morphological classifications and provides definitions of the sensilla of insects used for current descriptions of the twenty-four types of labial sensilla in the Nepomorpha.…”

“…These transverse bars are separated from each other by slightly sclerotized membranes in which the sense organs are located [10, 13, 14]. In particular, in the heteropterans the tips of the labium (two lateral lobes) have gustative sensilla, frequently the contact chemoreceptive sensilla, and rarely also the olfactive, hygro-, and thermoreceptive sensilla as well as the tactile sensilla [1, 15, 16]. Several types of these sensilla on the labial tip have been described in many species of the Pentatomomorpha [17–23], the Nepomorpha [1, 24] and the Gerromorpha [Brożek and Zettel, in prep].…”

“…Several types of these sensilla on the labial tip have been described in many species of the Pentatomomorpha [17–23], the Nepomorpha [1, 24] and the Gerromorpha [Brożek and Zettel, in prep]. A full documentation of different cuticular hairy structures of the mechanosensilla and chemosensilla on all segments of the labium in several species of the Triatominae (Cimicomorpha: Reduviidae) has been presented by Catalá [25] and on distal segment of the labium in the Peiratinae (Cimicomorpha: Reduviidae) by Brożek and Chłond [15]. A comprehensive study of the Triatominae and the Peiratinae species has shown that the types of the labial mechanosensilla and their numbers are similar in individual species.…”