Comparative Morphology Of The Mouthparts In Aphidoidea(Insecta: Hemiptera)

Mouthparts are the feeding apparatus of insects, and in various feeding structures have been modified to perform the ingestion of a vast diversity of food by different feeding strategies. Research on mouthpart morphology could provide insight on the feeding mechanisms and taxonomy of insects. A comparative study using scanning electron microscopy is documented on Aphidoidea including 9 families 10 species: Rhopalosiphum padi(L.), Sitobion avenae(Fabricius), Eriosoma lanigerum(Hausmann), Periphyllus koelreuteria Takahashi, Kurisakia onigurumi(Shinji), Anoecia fulviabdominalis(Sasaki), Phloeomyzus passerinii zhangwuensis Zhang, Ceratovacuna lonigera Zehntner, Greenidea ficicola Takahashi, and Cinara pinitabulaeformis Zhang et Zhang. The aims are to compare and analyze the morphological features of insect mouthparts in Aphidoidea, with a brief discussion of their putative functional significance.The mouthparts of Aphidoidea resemble those of other piercing-sucking insects, consisting of labrum, labium and stylet fascicle including a pair of mandibular stylets and a pair of maxillary stylets. The labrum is triangular, covering part of the labium. One pair of sensilla basiconica I is distributed on the joint of the labrum and anteclypeus. The labium has three types: 3-segmented labium, 4-segmented labium and 5-segmented labium. The labium is three-segmented in Ceratovacuna lonigera Zehntner and five-segmented in Greenidea ficicola Takahashi and Cinara pinitabulaeformis Zhang et Zhang, meanwhile the labia are four-segmented in Rhopalosiphum padi, Sitobion avenae(Fabricius), Eriosoma lanigerum(Hausmann), Periphyllus koelreuteria Takahashi, Kurisakia onigurumi(Shinji), Anoecia fulviabdominalis(Sasaki) and Phloeomyzus passerinii zhangwuensis Zhang. Two types of sensilla trichodea and two types of sensilla basiconica occur at different locations on the labium. A pair of sensilla basiconica is symmetrically distributed on the joint of the third and fourth segment. The labial tip has 8 pairs of sensilla basiconica, except for Cinara pinitabulaeformis Zhang et Zhang having 4 pairs.The stylet fascicle is composed of two separated mandibular stylets and two interlocked maxillary stylets. The inner surface of the mandibular stylets is smooth, and there are numerous ridges on each lateral side of these mandibular stylets. The two maxillary stylets are locked together by several processes, forming a larger food canal and a smaller salivary canal, and surrounded by two serrate-edged mandibular stylets. The maxillar has the sculpturing on the lateral margin of the distal extremity and 1-3 dentates protuberance at the very sharp tip. Also there is a common duct at the tip of the inner surfaces of maxillary stylets. A long depression in the center of the common duct can be found in Eriosoma lanigerum(Hausmann), Periphyllus koelreuteria Takahashi and Greenidea ficicola Takahashi.The gross morphological features of the mouthparts are similar to each other in Aphidoidea. There are significant differences among families. They are differences in the number of labial segment and length of each segment, the distribution and number of sensilla trichodea I and II, the number of serrate edges on the external surface of mandibular stylets, dentations and slant edges on the maxilla, and the presence or absence of the depression in the common duct. The diversity of the mouthpart morphology in Aphidoidea can be used in systematics.