Abstract
Mouthpart structure and feeding behavior in the temperate firebug, Pyrrhocoris sibiricus Kuschakevich, an important pest that feeds on seeds of leguminous and gramineous plants, are described for the first time. Mouthparts were observed using scanning electron microscopy to examine the external morphology, distribution and abundance of sensilla on mouthparts. Feeding performance by adults on both seeds and shoots were observed using a binocular microscope. The four-segmented labium contains 3 types of sensilla trichodea, 3 types of sensilla basiconica, 1 type of sensilla placodea and 1 type of sensilla campaniformia. Among them, sensilla trichodea are most abundant. The tripartite apex of the labium consists of two lateral lobes and an apical plate. Each lateral lobe possesses a field of 12 thick-walled uniporous peg sensilla and long non-porous hair sensilla. The mandibular stylet tips have three central teeth and two pairs of lateral teeth, which may help in penetrating hard seed coats. A series of scale-like projections are present on the inner surface of the mandibular stylets. The externally smooth maxillary stylets interlock to form a larger food canal and a smaller salivary canal, and there are five tubercles near the tip of the right stylet. Cross-sections of the stylet fascicle show that each mandibular stylet has a dendritic canal. The adult feeding process involves several steps, including exploring and puncturing of the host epidermis, a probing phase, an engorgement phase, and removal of the mouthparts from the host tissue. The structure and function of the mouthparts are adapted for the seed feeding habits.
Highlights
Functional requirements linked with feeding have let to the evolution of a wide variety of morphological modifications of mouthparts that played a prominent role in the evolution of insects
The piercing-sucking mouthparts of P. sibiricus resemble those of other heteropterans, arising from the front part of the head capsule and extending back along the ventral side of the body (Fig 1A)
The two inner maxillary stylets are partially surrounded by two somewhat shorter and serrate-edged mandibular stylets which are housed inside the labial groove, proximally covered by the small cone-shaped labrum
Summary
Functional requirements linked with feeding have let to the evolution of a wide variety of morphological modifications of mouthparts that played a prominent role in the evolution of insects. Such modifications permit these invertebrates to feed upon most organic materials [1]. Plant-feeding hemipterans feed using their specialized piercing-sucking mouthparts to puncture tissue and to suck on leaf cell contents, vascular fluids or plant seed contents [3]. Variation in the morphology of mouthparts, especially the types of sensilla present, is correlated with variation in food source and feeding behavior [4,5]. The study of mouthparts can provide insight into feeding mechanisms [6,7] and may provide important traits for use in assessing phylogenetic relationships [8]
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