Fine Morphology of the Mouthparts in Cheilocapsus nigrescens (Hemiptera: Heteroptera: Miridae) Reflects Adaptation for Phytophagous Habits

Abstract

To obtain a better understanding of feeding adaptations, the fine structure of the mouthparts in adults of Cheilocapsus nigrescens Liu and Wang, including the sculpture and interlocking mechanisms of the stylets and distribution and abundance of sensilla located on the labium, were studied using scanning electron microscopy. The mouthparts are similar to those of previously studied mirid species in most aspects and composed of a cone-shaped labrum, a tube-like, four-segmented labium with a deep groove on the anterior side, and a stylet fascicle consisting of two mandibular and two maxillary stylets. Each mandibular stylet tip has about 6–8 indistinctive notches, which help in penetrating the leaf surface. A series of transverse squamous textures are present on the adaxial surface of the mandibular stylets. The maxillary stylets interlock to form a food canal and a salivary canal, equipped with an external longitudinal process that engages grooves in the mandibular stylets. Three kinds of sensilla, including four types of sensilla basiconica (I, II, III, and IV), four types of sensilla trichodea (I, II, III, and IV), and one type of sensillum campaniformium, occur at different locations on the labium. Among them, sensilla trichodea I and II are the most abundant; sensilla basiconica II occurs between the first segment and second segment, and between the third and fourth segment. The tripartite apex of the labium consists of two lateral lobes and an apical plate. Each lateral lobe possesses a field of 11 sensilla basiconica IV and 1 sensillum trichodeum IV. The morphology of the mouthparts and the distribution of sensilla located on the labium in C. nigrescens are discussed with respect to their possible taxonomic and functional significance. In particular, the indistinct notches of the mandibular stylet and smooth inner surface of the right maxillary stylets are suited primarily for phytophagy.

How Does the Intricate Mouthpart Apparatus Coordinate for Feeding in the Hemimetabolous Insect Pest Erthesina fullo?

“…The labrum of E. fullo corresponds to the second group. This is similar to other true bugs, e.g., Pyrrhocoris sibiricus [52], Cheilocapsus nigrescens [53], and four species of Largidae (Physopelta quadriguttata, Ph. gutta, Ph.…”

“…To our knowledge, this is the first time that the detailed mouthpart morphology and feeding performance in a member of Pentatomidae have been reported together. The modified mouthparts of E. fullo have a number of morphological similarities to those heteropteran species described previously [17,19,22,37,44,[48][49][50][51][52][53][54][55], but our study revealed some new and interesting features that differ from those of other true bugs, and provide a better understanding of the feeding strategies and the sensory systems of E. fullo.…”

“…The labrum, a conspicuous anterior structure on the adult insect head, should play an important role in insect feeding. Recently the labrum was reinterpreted as fused paired appendages of an intercalary segment [56][57][58] and a few scholars have conducted detailed studies on its morphology in Heteroptera [52][53][54][55][59][60][61]. In previously published reports, the morphology of the labrum was used as a taxonomic feature of higher taxa of Heteroptera [59][60][61][62][63], but its structure varies according to feeding habits and mechanisms [61].…”

“…The labium of E. fullo has four segments as in most of other heteropteran bugs [27,[52][53][54][55]. Usually, when insects are feeding, the second segment approaches the first segment, allowing the head to be lowered as the stylet fascicle penetrates the food tissue.…”

“…Heteropteran stylets form a fascicle composed of two lateral mandibular stylets and two maxillary stylets; the former are armed with teeth or rasps and the latter interlock and forms the salivary and food canals [17,18,25]. As feeding and probing on host plants are responsible for the direct or indirect damage to plants by phytophagous hemipteran insects, the stylets, including the shape and dentition of the tips, have been studied previously in several heteropterans [17,18,20,49,50,[52][53][54][55][67][68][69][70][71][72][73][74][75]. In E. fullo, there are a series of squamous textures regularly distributed on the inner surface of the mandibular stylet and the left and right sides of the longitudinal groove are different.…”