The structure of extremely long mouthparts in the aphid genus Stomaphis Walker (Hemiptera: Sternorrhyncha: Aphididae)

Abstract

Scanning electron microscopy and light microscopy were used to elucidate the morphology of labium and mandibular and maxillary stylets of the aphids Stomaphis quercus (L.) and S. graffii Cholodkovsky. The mechanism of labium shortening associated with feeding process was described as well. Stomaphis quercus and S. graffii have cone-shaped labium of 13 and 10 mm in length, respectively, that strongly extend behind the abdomen. The stylets bundle comprises a pair of mandibular and maxillary stylets which are on average as long as labium. Serial cross sections of labium revealed that the first segment is inverted inside and the second is pulled into it; both segments are shifted into abdomen. This study provides new information on S. quercus and S. graffii mouthparts that may help to understand their feeding behavior.

Keywords: Feeding; Labium; Mandibles; Maxillae; Morphology.

Fig. 1

Mouthparts of Stomaphis graffii. a Shape and length of individual labial segments (I–Vs) in the rest, conical, short labrum (Lr), looped the stylets bundle (st)—mandibles (Mds) and maxillae (Mxs), lg labial groove in individual segments. b Natural position of the labium in living non-feeding aphid. Mouthparts of Stomaphis quercus. c Length of labium (Is–Vs) at rest. d, e Shortening the labium during feeding, parts of the first and second segments are visible

Fig. 2

Shape of the labium and length of stylets at rest in S. quercus. a Length of the labial segments Is–Vs. b A wide and more chitinous basal part of the first segment and the membranous connection with the head, c mb Membranous connection between the first and second segment, dorsal view. d Arrangement of the trichoid sensilla on the first and second segment, lateral view. e lg Shallow labial groove in the base of first segment. f ds Dorsal side of the first segment. g tr Trichoid mechanosensilla inserted in flexible sockets. h rb Reinforcement bars on the dorsal side of the second segment. S. graffii. i rb Reinforcement bars of the second segment in cross section visible inside the first segment

Fig. 3

Shape and length of the labium at rest in S. quercus. a Tubular shape of the segments IIIs, IVs and Vs in magnification. b Connection between III i IV segments, dorsal view. c lg Labial groove deeply placed in the third segment which housed the stylet bundle. d Labial groove of the third and fourth segment. e lg Wide labial groove in the fifth segment. f tr Trichoid mechanosensilla on the ventral side of the fifth segment

Fig. 4

Maxillae and mandibles in S. quercus. a Pointed tip of the maxillae: left (LMx) and right (RMx). b Ends of the mandibles with small barbs (br) on external side: left (LMd) and right (RMd). Evidence of inserting the second segment into the first. c The part of the first and second segment visible externally, the stylets bundle come into the groove in the third segment. d st Stylets rolled up in cr crumena inside of the head in the larva (S. graffii). Cross section by maxillae and mandibles S. graffii. e Maxillae (LMx, RMx) and mandibles (LMd, RMd) placed in groove of the labium. f System connection between the maxillae. dl dorsal lock, ml middle lock, vl ventral lock, sc salivary canal, fc food canal

Fig. 5

Feeding process in Stomaphis quercus. a Labial segments are situated at some angle to the plant surface, the first and second segments were pressed one into another, it was observed in living aphid. b The first and second segment are inserted into abdomen (i.Is + IIs). Externally, only the basal part of the first and distal part of the second segment are visible

Fig. 6

Different phases of shortening of the labium in Stomaphis quercus. a, b The first and second segments evidently shorter. c Surface of the first segment was reversed (i.mIs) and pulls the second segment. d Externally, a portion of the second segment is visible within the first, the stylets are free not placed in the groove. e Labrum, stylets, first and second labial segment during the shortening process. f Lr labrum reaching proximal part of the IVs segment the labium in the phase of feeding, stylets are distinctly protruding

Fig. 7

Note how the second segment is rolled in the first in Stomaphis graffii. a, b Shortening of the labium during feeding, part of the first and second segments placed inside the body, externally, a portion of the second segment is visible within the first. c Apodema (aIIs) of the second segment is placed inside the first segment. d A muscles (m) and apodema (aIIs) of the proximal part of the second segment. e Segment II of the labium has been pushed within the first segment forming a sheath (e.mbIs, i.mbIs) around the second (IIs). f Same as figure e, however, both segments are placed among internal organs in abdomen

Fig. 8

Model of shortening (withdrawing) the first two segments of the labium into abdomen during feeding in Stomaphis. a All labial segments (Is–Vs) protruding externally of head. b Inversion of the distal area of the first segment and pushing the proximal part of the second segment. c Entire surface of the first segment has been reversed and inside there is the second segment, both are localized in the body (thorax and partly in the abdomen). d Total reversal of the first segment and retracting of the second segment, both segments are placed in the abdomen. abd abdomen, es external surface, he head, is inverted external surface, lgb total body length, lgl length of the labium, m protractor muscles, th thorax, I–Vs number segments of the labium