Morphological Modification of the Mouthparts of Aphids (Hemiptera: Sternorryncha: Aphididae)

Comparative morphological analysis of the labrum and labium among nine aphid species-Uroleucon sp., Glyphina betulae, Myzus cerasi, Panaphis juglandis, Chaitophorus sp., Lachnus roboris, Forda sp., Paracletus cimiciformis, and Trama sp., belonging to six subfamilies-reveals marked interspecific variation in structure, segmentation, and sensilla equipment. The labrum is generally triangular and plate-like, ranging from 88.8 μm (M. cerasi) to 358.1 μm (L. roboris). However, Trama sp. exhibits a distinctive conical labrum (311.1 μm) bearing three pairs of sensilla trichodea (St2)-unique among the examined taxa. Most species possess a four-segmented labium, while Trama sp. and L. roboris exhibit five segments. The second segment is the longest and most elaborate, bearing dense arrays of sensilla or spiniform tubercles in several species. Sensilla trichodea (St1-St5) are widespread across taxa, showing the highest densities in Chaitophorus sp St1, Trama and L. roboris St2, Uroleucon sp St3, and P. cimiciformis St4, whereas Trama sp. uniquely combines sensilla St2, St3, St5, and sensilla basiconica (Sb2). Sensilla basiconica (Sb1) are consistently positioned at the base of the labrum and the fourth labial segment, except in Trama sp., which presents sensilla St3. Distinct cuticular modifications-including apical cuticular processes and granular protrusions-occur only in Trama sp. and L. roboris, suggesting lineage-specific adaptations. These morphological patterns indicate that aphid mouthpart diversity reflects functional specialisation linked to host-plant structural variation.