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.
Highlights
True bugs (Heteroptera) are a major clade of non-holometabolous insects within the insect orderHemiptera, comprising more than 42,000 described species and exhibiting a vast array of behavioral diversity in terms of feeding and habitat preference [1,2,3]
The mouthparts in hemipteran/heteropteran taxa consist of a short, conical labrum and a long, segmented labium, bisected dorsally by a labial groove within which lie the mandibular and maxillary stylets
The mouthpart structures of four Largidae species were investigated as examples of seed-feeding heteropterans
Summary
True bugs (Heteroptera) are a major clade of non-holometabolous insects within the insect order. Hemiptera, comprising more than 42,000 described species and exhibiting a vast array of behavioral diversity in terms of feeding and habitat preference [1,2,3]. Pentatomomorpha is one of the most diverse infraorders of Heteroptera. The great majority of the Pentatomomorpha families (phytophagous group) are plant-feeders, sucking phloem sap or parenchymal cell contents of monocotyledons and dicotyledons, as well as the endosperms of seeds and plant pollen [2,5,6]. The four fairly species-poor early diverging lineages within Heteroptera have retained predatory behaviors [7]. The evolution of feeding strategies in Heteroptera has been the topic of much debate. Cobben [8,9]
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