The Microscopic Morphology of Mouthparts and Their Sensilla in the Mycophagous Ladybeetle Illeis chinensis (Coleoptera: Coccinellidae)

Abstract

The morphological diversity of insect mouthparts is closely related to changes in food sources and diets. Research into the structures of insect mouthparts may help to establish a fundamental basis for a better understanding of insect feeding mechanisms. In this study, we examined the fine morphology of the mouthparts of Illeis chinensis using scanning electron microscopy. We paid particular attention to the types, quantities, and distribution of sensilla on the mouthparts. Our results showed that the basic components of the mouthparts of I. chinensis are the same as those in other lady beetles, i.e., the labrum, mandible, maxillae, labium, and hypopharynx. We also found structural specialization indicating adaptation to fungal feeding. On the mouthparts, there are eight kinds of sensilla and two kinds of glandular structures, including sensilla chaetica, sensilla basiconica, sensilla styloconica, sensilla coeloconica, sensilla campaniformia, sensilla placodea, sensilla digitiformia, Böhm bristles, perforated plates, and cuticular pores. This is the first time that sensilla digitiformia has been reported in ladybirds. Finally, variations in mouthparts among ladybirds with differing diets, as well as the putative functions of each of the mouthparts and sensilla, were discussed. This research can provide a reference for understanding the functions of the mouthparts in ladybird feeding behavior and thereby contribute to the development of precise insect behavior regulation and management strategies.

Keywords: Illeis chinensis; fine morphology; mouthparts; scanning electron microscopy; sensilla.

Figure 1

The overall morphology of Illeis chinensis adults and the mouthparts. (a) Dorsal view of the adult. (b) Ventral view of the adult. (c) Dorsal view of the head showing the position and morphology of the compound eyes, antennae, labrum (Lm), labial palpi (Lp), and maxillary palpi (Mp). (d) Ventral view of the mouthparts showing the position and morphology of maxillae (Mx), maxillary palpi (Mp), labium (Lb), and labial palpi (Lp).

Figure 2

Scanning electron micrographs of different kinds of sensilla and glandular structures on the mouthparts of Illeis chinensis: (a) sensilla chaetica I (Sch1); (b) sensilla chaetica II (Sch2); (c) sensilla chaetica III (Sch3); (d) sensilla basiconica I (Sb1), cuticular pores (Cp), and perforated plates (Pp); (e) sensilla basiconica II (Sb2); (f) sensilla basiconica III (Sb3); (g) sensilla styloconica I (Sty1); (h) sensilla styloconica I (Sty1) and sensilla styloconica II (Sty2).

Figure 3

Scanning electron micrographs of the sensilla and glandular structures on the mouthparts of Illeis chinensis: (a) sensilla coeloconica I (Sco1); (b) sensilla coeloconica II (Sco2) and sensilla campaniformia (Sca); (c) sensilla campaniformia (Sca); (d) sensilla styloconica I (Sty1), sensilla placodea (Sp), and cuticular pores (Cp); (e) sensilla digitiformia (Sd) and sensilla chaetica I (Sch1); (f) Böhm bristle (Bb); (g) perforated plates (Pp), sensilla chaetica I (Sch1), and cuticular pores (Cp); (h) cuticular pores (Cp).

Figure 4

Scanning electron micrographs of the labrum of Illeis chinensis. (a) Dorsal view of the labrum; (b) enlarged view of the dashed box in (a) showing sensilla chaetica I (Sch1), sensilla chaetica II (Sch2), perforated plates (Pp), and cuticular pores (Cp); (c) ventral view of the labrum; (d) enlarged view of the solid box in (c) showing sensilla basiconica III (Sb3) and cuticular pores (Cp); (e) enlarged view of the dashed box in (c) showing sensilla campaniformia (Sca) and sensilla coeloconica I (Sco1); (f) enlarged view of the dotted box in (c) showing the sensilla campaniformia (Sca) and sensilla coeloconica II (Sco2); (g) coniform processes; (h) palmate processes; (i) scaly processes.

Figure 5

Scanning electron micrographs of the mandible of Illeis chinensis. (a) Dorsal view of the left mandible; (b) dorsal view of the right mandible; (c) enlarged view of the point line box in (b) showing dorsal condyle (Dc); (d) ventral view of the right mandible; (e) ventral view of the left mandible showing ventral teeth (Vt), dorsal teeth (Dt), prostheca, and ventral condyles (Vc); (f) enlarged view of the point line box in (e) showing ventral condyles (Vc); (g) enlarged view of the solid box in (a) showing the sensilla basiconica I (Sb1), perforated plates (Pp), and cuticular pores (Cp); (h) enlarged view of the dotted line box in (e) showing the ventral view of prostheca; (i) spiny processes on the dorsal side of prostheca; (j) ventral view of the molar teeth of right mandible; (k) ventral view of the molar teeth of left mandible; (l) ventral view of incisor.

Figure 6

Scanning electron micrographs of the maxillae of Illeis chinensis. (a) Ventral view of the right maxillae showing maxillary palp (Mp), galea (Gal), lacinia (Lac), stipes (Stp), and cardo (Crd); (b) ventral view of the left maxillae; (c) ventral view of the tip of galea showing sensilla chaetica I (Sch1) and sensilla basiconica III (Sb3); (d) ventral view of the lacinia showing sensilla chaetica I (Sch1), sensilla basiconica I (Sb1), and perforated plates (Pp); (e) dorsal view of the galea and lacinia showing sensilla basiconica I (Sb1); (f) enlarged view of the point line box in (e) showing the Böhm bristle (Bb); (g) dorsal view of the right maxillary palp showing sensilla chaetica I (Sch1) and sensilla digitiformia (Sd); (h) ventral view of the maxillary palp showing sensilla basiconica II (Sb2); (i) enlarged view of the dashed box in (h) showing the sensilla styloconica I (Sty1), sensilla styloconica II (Sty2), and sensilla basiconica II (Sb2).

Figure 7

Scanning electron micrographs of the labium of Illeis chinensis. (a) Ventral view of the labium showing ligula (Lig), labial palp (Lp), prementum (Prmt), and postmentum (Pomt); (b) enlarged view of the solid box in (a) showing the sensilla styloconica I (Sty1), sensilla basiconica I (Sb1), sensilla placodea (Sp), and cuticular pores (Cp); (c) enlarged view of the dashed box in (a) showing the sensilla chaetica III (Sch3), sensilla basiconica I (Sb1), and cuticular pores (Cp); (d) enlarged view of the point line box in (a) showing sensilla chaetica I (Sch1) and cuticular pores (Cp); (e) Dorsal view of the labium; (f) enlarged view of the dashed box in (e) showing epidermal processes.