Togepsylla tibetana (Yang & Li, 1981)

Luo, Xinyu, Cai, Wanzhi & Qiao, Gexia, 2017, Half-jumping plant lice - a taxonomic revision of the distinctive psyllid genus Togepsylla Kuwayama with a reassessment of morphology (Hemiptera, Psylloidea), ZooKeys 716, pp. 63-93 : 73-77

Togepsylla tibetana (Yang & Li, 1981) Figs 4, 8, 12, 27, 28, 32

Hemipteripsylla tibetana Yang & Li, 1981: 182; Li 2011: 209.

Togepsylla tibetana (Yang & Li): Hodkinson 1990: 716.

Diagnosis.

Paramere with large area of netlike grains covering the inner surface of apical half, anterior margin serrated (Figs 27, 28). Female proctiger short, curved upwards only at the tip (Fig. 32).

Redescription.

Adult coloration. Ground color yellow. Long and thick setae on dorsum yellow. Compound eyes grey. Ocelli yellow. Antennae yellow, with black spices on segments IV, VI, VIII; segments IX-X entirely black. Fore wing hyaline and colorless (Fig. 12). Male and female terminalia yellow.

Structures: Setae on dorsum of body relatively short (Table 1) and based on smooth projections. A pair of small tubercles present above toruli (Fig. 4). Gena moderately swollen bilaterally (Fig. 4). Antennal segments IV-IX each with a single rhinarium on the apex, segments IV, VI and VIII each with an extra rhinarium; all rhinaria with horn-shaped projections; proximally based terminal seta about equally long with the distally based one (Fig. 8).

Mesoscutum with five pairs of prickly setae. Metatibia with one row of thick setae ventrally, and with a tightly packed row of long setae on the dorsum. Pulvilli narrow. Fore wing with broad cell r1, cell cu1 tallest in the middle; vein M3+4 with one seta on the base; surface spinules rather minute, widely spread across a large area in distal cells; fields of radular spinules unclear (Fig. 12).

Pore fields on abdominal ventrum large oval, with pores loosely packed.

Male terminalia: Proctiger completely sealed, with apex slightly thickened (Fig. 27). Paramere broad lamellar, with rather slender base; anterior margin of apical half emarginated, thin and serated; posterior margin with a basal ridge; apical half of inner surface with netlike grains; anterior angle with a few short and thick setae on inner surface; posterior margin with a row of inner-curved short setae on apical half (Figs 27, 28). Aedeagus curved backwards apically, dorsum lacking tiny spines, tip forming a small acute hook (Fig. 27). Subgenital plate near rectangular in profile, dorsal-apical angle with one long seta, ventral surface with sparse setae (Fig. 27).

Female terminalia (Fig. 32): Short and broad in overall shape. Apex of proctiger moderately curved upwards; apical half of proctiger with nearly evenly spaced setae, and with a row of setae along ventral margin of apical process. Subgenital plate with blunt and retracted apex, ventral surface with sparse setae.

Fifth instar immature. Unknown.

Material examined.

CHINA: 49 ♂, 69 ♀, Tibet, Nyingchi, Mafenggou, 3050 m, ex Litsea sericea , 1.vi.1978, Fasheng Li (CAU, type series).

Host plant.

Litsea sericea (Nees.) Hook. f. ( Lauraceae )

Distribution.

China: Tibet.

Biology.

Yang and Li (1981) recorded that the adults gather among the clusters of young leaves by large amount. The record of a habit similar with T. takahashii by Li (2011) seems artificial.

Differences between Togepsylla and Syncoptozus

The similarities and differences of the two genera have been listed by Hodkinson (1990). Nevertheless, some supplements can still be made here. Togepsylla possesses no median suture or discal foveae on the vertex; while Syncoptozus has the anterior section of median suture present, and S. bifurcatus possesses discal foveae ( Brown and Hodkinson 1988). Togepsylla has rhinaria on antennal segments IV-IX, sometimes even segment III, and often with additional rhinaria; Syncoptozus has only one rhinarium on apex of segments IV, VI, VIII, and IX each.

Reassessment of morphology

Hind legs

Psyllids jump powerfully, then cast a mid-air rotation. Such a somersault, however, involves not only the strong muscles supported by the specialized metathoracic furca, enlarged metatrochanteral tendon and expanded meral part of the metacoxa but also a kicking of both hind legs on parallel planes ( Burrows 2012), which are also parallel to the longitudinal body axis. This longitudinal placement of hind legs is caused by an inward twist of the metacoxa.

To discuss the formation of the enlarged and twisted metacoxa, one must seek reference from the mesocoxa. Mid and hind legs are both appendages of winged thoracic segments; additionally, in immature psyllids, they are equal in every detail, although differing from the forelegs in some aspects, indicating that hind legs of adults emerged from the model of mid legs. An undescribed Cacopsylla species is used as example:

The mesocoxa (Fig. 54) are relatively small and are connected to the coxal condyle of the mesopleurite by a dorsal-most articulation. Starting from the articulation, a thickened vertical edge runs down the outer surface, facing the lateral aspect, and is termed here as the 'dorsal edge’ of the coxa. The coxa connects to the trochanter via two 'trochanteral condyles’, which are longitudinally positioned, thus respectively termed ‘anterior-’ and 'posterior trochanteral condyle’. Such longitudinal positioning of trochanteral condyles places the mid legs on a transverse plane, a plane nearly perpendicular to the longitudinal body axis. Besides, a normally developed trochanteral tendon originates on the inner-dorsal edge of the mesotrochanter, stretching into the chamber of the mesocoxa, clinging onto the corresponding muscles.

Compared with mesocoxa, the metacoxa (Fig. 55) first experienced an enlargement of the coxal wall, which pivots over the elongation of the dorsal edge and is primarily characterized as the expansion of the prearticular part of the coxal wall and thickening of the meron. Simultaneously, because of the unequal development of the prearticular part and the meron, the entire metacoxa is twisted backwards at approximately 90°, turning the two trochanteral condyles into a transverse position. The plane of hind leg is therefore turned longitudinal (Figs 66, 67). This pair of straightly backwards-reaching hind legs provides a much better concentration of jumping force, thereby driving the powerful jump described above. Additionally, the trochanteral tendon is magnified and possesses a tortuous apex, serving to support the strong jumping muscles.

By contrast, Togepsylla possesses half-modified metacoxae (Fig. 56). The enlargement is almost complete, but the positioning of the two trochanteral condyles is shifted at a limited level. For this reason, the hind legs of Togepsylla retain a posture similar to that of the middle legs, as shown in the habitus photograph (Fig. 64). Additionally, the trochanteral tendon is also half-enlarged: the relative size is much smaller, and the apex, although also expanded, is a simple flat surface instead of tortuous. According to the field observations by Xinyu Luo, adults of Togepsylla glutinosae sp. n. can only leap forward like frogs, at a short distance and without mid-air rotations.

Lateral aspect of thorax

Most psyllids possess an apophysis on meso- and metepisternal complex, termed 'trochantinal apodeme’ ( Ouvrard et al. 2002). This is an autapomorphy of Psylloidea. For mesopleuron, this structure may be on the anterior margin or median portion, depending on the taxon ( Ouvrard et al. 2002). However, there are some cases like Togepsylla and Pseudophacopteron in which the trochantinal apodeme is placed on the anterior margin and reduced to an obscure vestige.

According to Ouvrard et al. (2002), the modification of psyllid metapleurite relative to mesopleurite is due to a curving of the pleural sulcus. For the metapleurite of most psyllids, taking Cacopsylla as example, the pleural sulcus turns downwards over the coxal condyle, becoming congruent with the elongated and internally ridged dividing suture of episternum and trochantin (Fig. 58). In Togepsylla , the metapleuron represents a halfway modification. The dividing suture of metepisternum and trochantin is absent, the trochantinal apodeme is shallow and in anterior position, as in mesothorax (Fig. 57).

Wax-secreting fields on abdominal sternites

Togepsylla possesses three pairs of fields of pores on sternites of abdominal segments 4-6, in both sexes. Wax secretions from these pores have been observed on T. matsumurana (Fig. 62). Similar structures, several pairs of wax plates composed of many small wax-secreting pores, is one of the defining characters of adult whiteflies: Whiteflies kick the wax secretions of these glands with the hind legs, and then spread the shattered wax particles over the entire body surface ( Byrne and Bellows 1991). In females of Aleyrodinae, two pairs of wax plates are found, on segments 3-4, whereas in Aleurodicinae, four, on segments 3-6; in males of Aleyrodinae, four pairs are present on segments 3-6, whereas three pairs appear on segments 3-5 in Aleurodicinae and Udamoselinae ( Gill 1990; Martin 2007).

All the four members of Sternorrhyncha are known to secrete wax through integumental wax gland/pores. In scale insects whose wax glands are studied the most, these structures are highly variable in ultrastructure (shape and number of loculars of each pore) and distribution (all over the body or restricted to a certain region) ( Foldi and Pearce 1985; Foldi and Lambdin 1995). Some aphid families/subfamilies possess wax gland plates, which also vary in shape and distribution, on body dorsum ( Chen and Qiao 2012). These, however, are not so far known to reveal the same arrangement as Togepsyllinae and whiteflies, nor does the lack of detailed ultrastructural study of Togepsyllinae support their resemblance.

Psyllid immatures possess wax-secreting pores on their caudal plates. These pores are arranged in various patterns, mostly with a basic circum-anal ring (possibly homologous with the circum-anal ring of female adults), and on many occasions with extra pore fields (Brown and Hodlinson 1985). Extra pore fields can sometimes be succeeded by the adults, appearing on their more terminal (usually segments 7 and/or 8) abdominal tergites, e.g. Agonoscena pegani Loginova, 1960 and A. sabulisa Li, 1994 (in Li et al. 1994) ( Luo 2016). Although it is not currently possible to accurately decide the homology between abdominal segments between immatures and adults, one can still roughly judge and count the separate segments of immatures by the dorsal and ventral setae rows. So far, the immature of not any species possess wax secreting pores on areas that are possibly homologous with abdominal sternites 4-6.

This is the first time that a psyllid adult is found with such fields of wax-secreting pores. Compared with those of whiteflies, wax pore fields of Togepsylla are strongly constricted, and the segment correspondence is different. It is uncertain whether these structures of Togepsylla and Aleyrodoidea are homologous or not.