Morphological Disparity of the Mouthparts in Polyphagous Species of Largidae (Heteroptera: Pentatomomorpha: Pyrrhocoroidea) Reveals Feeding Specialization

Abstract

Mouthpart structures were observed in four species of Largidae using scanning electron microscopy to investigate their morphological disparity, and linked to changes in feeding specialization. The examined species are pests that feed mainly on seeds and plant sap of forbs, shrubs, and trees. Their external mouthparts are described in detail for the first time herein. The cone-like labrum and four-segmented tube-like labium are shorter in Physopelta species than in Macrocheraia grandis (Grey). The labium surface in all studied species bears nine types of sensilla (St1-St2, Sb1-3, Sch, Sca1-2, Sm). The distributions of sensilla on particular labial segments varies among the studied species. The tripartite apex of the labium consists of two lateral lobes and an apical plate that is partly divided in Physopelta species, and not divided in Macrocheraia. Each lateral lobe possesses a sensillar field with 10 thick-walled uniporous sensilla basiconica, one multiporous sensillum styloconicum, and one long non-porous hair sensillum. Each mandibular stylet tip in M. grandis has a central tooth placed anteriorly and pairs of teeth arranged dorso-laterally. In Physopelta, there are one or two central teeth placed anteriorly but two pairs of teeth dorso-laterally. In all studied species, the inner surfaces of the mandibular stylets have scale-like projections. A left–right asymmetry of the maxillary stylets is noticeable; the external end of the right maxillary stylet is smooth and slightly tapered in M. grandis and evidently wider (spoon–like) in the three species of Physopelta, while the left end of the stylets is straight and narrow in M. grandis in contrast to Physopelta, in which the end is straight and wide. No differences in the internal structure of the maxillary stylets were observed among the studied species. Based on structural differences, we inferred that the mandibles and maxillae are more adapted for seed-sucking in Physopelta species than in M. grandis. M. grandis has the ends of the maxillae more narrowed, a trait more adapted for sucking sap from phloem or parenchymal cells.

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

“…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.…”

“…gutta, Ph. cincticallis, and Macrocheraia grandis) [55]. We observed regular wrinkles from base to end on the ventral surface of the E. fullo labrum.…”

“…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.…”

First description and comparison of the morphological and ultramicro characteristics of the antennal sensilla of two fir longhorn beetles

“…Sensilla are differentiated according to morphology such as Böhm bristles, chaetica, trichodea, basiconca, coeloconica, campaniformia, and others. These sensilla types have been reported in a variety of insects [ 17 – 19 ]. Therefore, the distribution and number of sensilla with different functions may affect the reception of information, as related to specific searching behavior of insects [ 20 ].…”