Rhizoecus coffeae Laing

Hodgson, Chris, 2012, Comparison of the morphology of the adult males of the rhizoecine, phenacoccine and pseudococcine mealybugs (Hemiptera: Sternorrhyncha: Coccoidea), with the recognition of the family Rhizoecidae Williams 3291, Zootaxa 3291 (1), pp. 1-79 : 21-24

Rhizoecus coffeae Laing

( Fig. 5 )

Rhizoecus coffeae Laing, 1925: 384 .

Material examined. Surinam (Dutch Guinea), no other locality, on roots of coffee ( Rubiaceae ), no date, G. Bünzli ( BMNH): 2/4ad ♂♂ in moderate to poor condition, not stained, all wings absent .

Mounted material: probably brachypterous (but most of wings missing); very small, total body length about 750–770 µm; antennae much less than half total body length, most segments barrel-shaped (but number of segments highly variable), with both hair-like setae (hs) and fleshy setae (fs), but these difficult to separate; body highly hirsute, all hs, robust and mainly 20–24 µm long; fleshy setae (fs) apparently absent; loculate pores (lp) with 4–6 loculi, each about 6–7 µm wide.

Head: greatest width about 125–135 µm. Dorsal epicranium lightly sclerotised throughout; with many robust hs dorsal head setae (dhs) distributed along full length of head; loculate pores absent. Genae not differentiated from rest of head and without genal setae. Eyes: 2 pairs of round, simple eyes (se), subequal in size, each 20–25 µm wide. Ventral epicranium also lightly sclerotised, with a small area of sclerotisation anteriorly representing lateral arms of midcranial ridge (lmcr); with 4 or 5 pairs of ventral midcranial ridge setae (vmcrs), longest about 40 µm long. Preocular ridge (procr) short, restricted dorsally to just posterior to each scape; ventrally, procr present as thin ridges anterior to ventral simple eyes.

Antennae: number of segments very variable, from 5–7 (when 5 segmented, considered that segments IV and V fused, and VI and VII fused); data here refer to 7-segmented antenna: 265–275 µm long (ratio of total body length to antennal length 1:0.36). Scape (scp): 20–30 µm long, 40–42 µm wide, with 4 hs. Pedicel (pdc): length 35–38 µm, width 33–33µm; with concentric ridges on distal end; with 0 or 1 fs, 5–7 hs + a campaniform pore. Segments III–X all rather barrel-shaped, with narrow intersegmental membranes; greatest width 21–27 µm; lengths of segments (µm): III 41–47; IV 38–42; V 34–38; VI 46–48, and VII 58–60; fs about 30–34 µm long; longest hs about 48–52 µm; approximate number of setae per segment: III–V 8 or 9 fs + 1–3 hs; VI 9 fs, 2 hs + 2 large bristles (ab); VII 19 fs, 2 or 3 hs + 3 ab (all fs-like); long setae not apparently differentiated from fs.

Thorax. Prothorax: swollen somewhat laterally and rather long; setae abundant over most of dorsal and pleural areas. Ventrally, setae hard to discern but possibly with no prosternal setae but maybe with a few anteprosternal setae (astn 1 s); antemesospiracular setae (am 2 s) present as a group just posterior to each procoxa, fusing with pleural setae laterally; lp absent. A nipple-like structure present between procoxae, with 5 or 6 long setae, each about 15– 18 µm long (labium?).

Mesothorax: apparently only lightly sclerotised. Prescutum (prsc) rectangular and unusually short, 26–28 µm long, 100–120 µm wide; prescutal ridge (pscr) moderately well developed; prescutal suture absent; with perhaps 2 or 3 pairs of hs prescutal setae (prscs). Scutum (sct): distance between prescutum and scutellum uncertain but perhaps about 50 µm; scutal setae (scts) abundant, in a broad band across segment. Prealare (pra) well developed, each bent posteriorly at apex; with a small sclerotisation just laterad to each prescutal ridge representing apodeme on anterior margin near prealare (pra); triangular plate (tp) probably represented by a narrow sclerite. Scutellum (scl) unusually wide, 100–110 µm wide, 36 µm long; without a distinct scutellar ridge and no foramen; with many scutellar setae (scls). Mesopostnotum (pn 2) and postnotal apophysis (pna) narrow. Basisternum (stn 2) rather wide, 130–140 µm wide, about 70–90 µm long; bounded anteriorly by a weak marginal ridge (mr) (absent medially), and posteriorly by a fairly strong precoxal ridge (pcr 2); with few basisternal setae (stn 2 s), perhaps 5 pairs; lateropleurite (lpl) moderately broad, unreticulated, and with a strong extension from marginal ridge along anterior margin; furca (f) well developed, narrow-waisted, arms very divergent but short. Mesoprecoxal ridge (plr 2) with a short additional ridge extending ventrally from near coxal articulation. Mesothoracic spiracle (sp 2): width of peritreme about 18 µm. Postmesospiracular setae (pm 2 s) 7–10 hs + 1 or 2 lp on each side posterior to each spiracle, plus 1 pair of hs medially. Tegula (teg) large, with 6–8 hs tegular setae (tegs).

Metathorax: with a broad band of hs extending across full width of segment, representing metatergal setae (mts) and dorsospiracular setae (dss); metapostnotal sclerite (pn 3) possibly absent. With a small group of postmetaspiracular seta (eps 3 s) + 0 or 1 lp on each side. Metepimeron (epm 3) sclerotised, but without setae. Antemetaspiracular setae (am 3 s): 1 hs. Metathoracic spiracle (sp 3): width of peritreme about 18 µm, with 0 or 1 associated lp. Metasternum (stn 3) with abundant hs anterior (amss) and posterior metasternal setae (pmss) but no lp.

Wings: both missing bar a few basal sclerites but these resemble those of Rh. dianthi and therefore probably brachypterous; only 1 alar seta visible; presence of alar sensoria uncertain. Hamulohalteres absent.

Legs: metathoracic legs longest. Coxae (cx): I 66–68; II 66; III 70–75 µm long; coxa III with about 8 hs. Trochanter (tr) + femur (fm): I 126–130; II 124–126; III 130–140 µm long; trochanter III with about 5 hs; each trochanter with 3 roundly oval sensoria arranged in a triangle medially; with strong Y-shaped ridges; long trochanter seta not differentiated but seta in this position about 16 µm long; femur III with about 7–10 hs. Tibia (ti): I 75–78; II 73–75; III 85–90 µm; tibia III with a total of about 7–13 setae, mainly hs, becoming spur-like distally; all tibiae with 2 apical spurs (tibs); length of longest 25–28 µm. Tarsi (ta) 2 segmented, proximal segment very short and ring-like; length of both segments combined: I 58–65; II 58–60; III 56–66 µm long (ratio of length of tibia III to length of tarsus III 1:0.7); tarsus III with 7–9 setae, mainly spur-like; tarsal digitules (tdgt) represented by a pair of very short setae on either side of distal end of tarsus. Claws (c) long and narrow, without a denticle; length: III 30– 33 µm; claw digitules (cdt) setose, each about 16 µm long.

Abdomen: segments I–VII: all tergites (at) and sternites (as) lightly sclerotised; pleurites present on VIII but otherwise absent. Caudal extension of segment VII absent. Loculate pores (lp) absent ventrally and perhaps pleurally, but with a single pair of pores on dorsum of all or most segments and up to 2 or 3 on posterior two segments; dorsal setae (ads) abundant in broad segmental bands which fuse with pleural setae laterally; pleural setae (dps) dense but separated from ventral abdominal setae (avs) by a gap on segments II–VI; avs otherwise also in broad, dense bands. Segment VIII: tergite (at) and sternite (as) lightly sclerotised; tergite with 2 pairs of hs dorsal abdominal setae (ads) medially and 1–3 lp; sternite with 0 or 1 seta but no pores; caudal extension absent, with a few short ventral pleural setae on each side plus 2 long setae (length 46–60 µm) in position of glandular pouches, each 50–55 µm long.

Genital segment: penial sheath (ps) triangular, narrowing to a sharp point; length from anterior margin to apex 104–108 µm, width at widest point 80–86 µm. Dorsally with a wide anus (width perhaps 23 µm) at anterior end; dorsally with 4–6 longish setae on each side, each about 25 µm long. Ventrally with a wide slit through which aedeagus (aed) emerges; borders of opening with a line of 2 or 3 hs, each about 25–28 µm long, plus a pair of rather shorter setae near anterior margin. Aedeagus (aed) strongly curved, perhaps 90 µm long, with parallel margins when viewed dorsally and sharply pointed, with apex emerging under pointed extension of penial sheath; anteriorly bending ventrally and fusing with a short sclerotised basal rod (bra). Apex of penial sheath with a few small sensilla (psp).

Comment. Although both wings are missing, it is here considered that the males of Rh. coffeae are probably brachypterous (rather than macropterous) because: (a) the body shape and structure are very similar to the brachypterous Rh. dianthi Green , described below; (b) the mesothorax appears to be poorly sclerotised, suggesting weak or absent wing muscles, and (c) the structure of metathorax dorsally is very similar to abdominal segments.

The homology of the "nipple-like" structure present ventrally between the procoxae is uncertain; it might represent the position of the labium but it seems unlikely that this would have a group of such robust setae; or perhaps it is related to the "mammillate organ" present at the anterior end of the prosternum of some Phenacoleachia species ( Theron, 1962; Hodgson & Foldi, 2006).

The male of Rh. coffeae differs from those of the other species seen here in having the following combination of character states: (i) body highly hirsute; (ii) presence of the "nipple-like" structure on the venter of the prothorax, and (iii) 5- to 7-segmented antennae.

Figures

FIGURE 5. Rhizoecus coffeae Laing. Adult male. Where A = hair-like seta; B = fleshy seta; C = loculate pores; K = distal end of posterior leg, and Z =?labium. For other labels, see under Materials and methods: conventions.