Rhizoecus dianthi Green

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 : 24-26

Rhizoecus dianthi Green

( Fig. 6 )

Rhizoecus dianthi Green, 1926: 175 .

Material examined. U.S.A., Wyoming, Albany Co., Laramie, in soil of African violet ( Saintpaulia sp. , Gesneriaceae ), 14.v.1980, E.W. Speckman ( USNM): 2/2ad ♂♂ (in moderate to good condition).

Mounted material: brachypterous, very small, total body length about 740–750 µm; wings short and narrow, only about 1/2 total body length and about 1/4th as wide as long. Antennae a little more than half total body length, most segments barrel-shaped, with hair-like (hs) and fleshy setae (fs), these sometimes difficult to separate; body with few setae, all hs, robust and mainly 20–30 µm long; fleshy setae (fs) apparently absent; loculate pores (lp) with 5 loculi, each about 5 µm wide.

Head: greatest width about 125 µm. Dorsal epicranium lightly sclerotised throughout; with (on each side) about 7 or 8 robust hs dorsal head setae (dhs) distributed along full length of head; loculate pores absent. With 2 pairs of simple eyes (se), each 25–30 µm wide. Genae (g) without genal setae. Ventral epicranium also lightly sclerotised, with a short ventral midcranial ridge (vmcr) and small lateral arms (lmcr); with 4 or 5 pairs of ventral midcranial ridge setae (vmcrs), longest about 30 µm long. Preocular ridge (procr) short, dorsally extending along dorsal margin of ocular sclerite; ventrally, procr present as a thin ridge over each ventral simple eye.

Antennae: 10-segmented; 370–445 µm long (ratio of total body length to antennal length 1:0.55). Scape (scp) squarish: 35–37 µm long, 35–40 µm wide, with 4 hs. Pedicel (pdc): length 45–50 µm, width 30–32 µm; with concentric ridges on distal end; with 7 fs (mostly ventral), 6 or 7 hs + a campaniform pore. Segments III–X all rather barrel-shaped, with narrow intersegmental membranes; lengths of segments (µm): III: 50; IV: 36–42; V: 36–40; VI: 40–42; VII: 40–44; VIII: 42–44 and IX: 50–52; fs about 26–30 µm long, hs longer, each slightly slimmer than fs and 36–42 µm long, longest on distal segments, setae more or less in two whorls; approximate number of setae per segment: III 3–6 fs + 2 or 3 shortish hs; IV–VI 6–9 fs + 2 long hs; VII 9–12 fs + 2 or 3 long hs; VIII & IX 10–12 fs + 2 or 3 long hs + 1 antennal bristle (ab), and X 16 or 17 fs, 3 or 4 hs + 3 narrow bristles (similar to fs).

Thorax. Prothorax: swollen somewhat laterally; with 6–10 hs propleural setae (pl 1 s) + 1 or 2 lp on each side. Median pronotal (mpns) setae: total of 4 hs + 2 or 3 lp; post-tergite (pt) possibly present, with 3 hs post-tergital seta (pts) in this position. Ventrally, with 2 hs antemesospiracular setae (am 2 s) but no lp. Sternum (stn 1) with 0 or 1 prosternal seta or 0 or 1 lp on each side. Anteprosternal setae and lp absent.

Mesothorax: prescutum (prsc) oval to rather rectangular, 36–38 µm long, 68–72 µm wide; prescutal suture absent; with 0–2 pairs of hs prescutal setae (prscs). Scutum (sct) with some transverse ridges; distance between prescutum and scutellum (scl) 36 µm; scutal setae (scts): 6–8 hs in total. Prealare (pra) well developed; apodeme either unclear or absent from anterior margin near pra; triangular plate (tp) distinct. Scutellum (scl) 60–65 µm wide, 30 µm long; without a distinct scutellar ridge and no foramen; scutellar setae (scls): 6–8 hs in total. Basisternum (stn 2) 110–120 µm wide, about 78 µm long; bounded anteriorly by a weak marginal ridge (mr) (absent medially), and posteriorly by a fairly strong precoxal ridge (pcr 2); with a total of about 7 hs basisternal setae (stn 2 s); lateropleurite (lpl) moderately broad, 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 13 µm. Postmesospiracular setae (pm 2 s): 4 or 5 hs + 1 or 2 lp on each side posterior to each spiracle, plus 1 hs medially. Tegula (teg) large, with 2 hs tegular setae (tegs).

Metathorax: with 2–5 robust hs metatergal setae (mts) + 0–2 lp; metapostnotal sclerite (pn 3) possibly absent. Dorsospiracular setae (dss): 3 or 4 hs on each side. Metepisternum (eps 3) with 1 postmetaspiracular seta (eps 3 s) on each side but these in line with posterior metasternal setae (pmss); metapleural ridge (plr 3) with a short additional ridge extending ventrally from near coxal articulation. Metepimeron (epm 3) sclerotised, but without setae. Antemetaspiracular setae (am 3 s) absent. Metathoracic spiracle (sp 3): width of peritreme about 13–14 µm, with 2 associated lp. Metasternum (stn 3) with a total of 4 hs anterior metasternal setae (amss) and 2 pairs of posterior metasternal setae (pmss) but no lp.

Wings: clearly brachypterous; hyaline, each 370–445 µm long, 100–105 µm wide (ratio of length to width 1:0.25; ratio of total body length to wing length 1:0.55); with distinct microtrichia; alar lobe (al) very small or absent; each wing with 2 hs alar setae (als) + 2 circular sensoria (sens) close to base of wing. Hamulohalteres absent.

Legs: metathoracic legs longest. Coxae (cx): I: 74–76; II: 74; III: 74–75 µm long; coxa III with about 11–13 hs. Trochanter (tr) + femur (fm): I: 153–162; II: 140–145; III: 165–168 µm long; trochanter III with about 5 or 6 hs; each trochanter with 3 roundly oval sensoria arranged in a triangle medially and with strong, Y-shaped sclerotised ridges; long trochanter seta not differentiated but seta in this position about 16 µm long; femur III with about 14–16 hs. Tibia (ti): I: 125–127; II: 117–120; III: 145–160 µm; tibia III with a total of about 20–23 setae, mainly hs, becoming spur-like distally; all tibia with 2 apical spurs (tibs); length of longest 18–22 µm. Tarsi (ta) two segmented, proximal segment very short and ring-like; length of both segments combined: I: 66–68; II: 62–70; III: 75 µm long (ratio of length of tibia III to length of tarsus III 1:0.61); tarsus III with 16–19 setae, mainly spur-like; tarsal spurs not differentiated; tarsal digitules (tdgt) considered to be absent. Claws (c) very long and thin, without a small denticle; length: III: 30 µm; claw digitules (cdt) finely pointed, each about 16 µm long.

Abdomen: segments I–VII: all tergites (at) and sternites (as) lightly sclerotised. Loculate pores (lp) absent dorsally and ventrally, but 0–3 present laterally on each segment; dorsal setae (ads) in lines of 2–4 hs on each side; plus 2 or 3 dorsopleural setae (dps) on each side + 0–3 lp and perhaps 1 ventropleural seta (vps) on each side of segments II–VII. Ventral abdominal setae (avs): a total of 4 across each segment. Segment VIII: tergite (at) lightly sclerotised; sternite (as) with a narrow band of sclerotisation around anterior margin of penial sheath; tergite with 2 pairs of hs dorsal abdominal setae (ads) medially; sternite without setae or pores; caudal extension (ce) rounded, each with 1 hs ventral pleural seta + 2 long setae (length 46–60 µm) in position of glandular pouches + 1 or 2 lp.

Genital segment: broad anteriorly, narrowing to a blunt apex; length from anterior margin to apex about 130 µm, width at widest point 85–96 µm. Dorsally with a lightly sclerotised bulbous ridge; anus about 18 µm wide; with 4 longish setae on each side, each 25–35 µm long. Ventrally, with a median slit-like opening through which aedeagus emerges; borders of slit lightly sclerotised, with a band of 5 short hs laterally, each 11–20 µm long. Aedeagus (aed) strongly curved with a blunt apex; perhaps 100 µm long, with parallel margins when viewed dorsally and sharply pointed, with apex emerging under pointed extension of penial sheath, but anteriorly bending ventrally and fusing with a short, sclerotised basal rod (bra). Apex of penial sheath with a few small sensilla (psp).

Comment. Of the adult males seen during this study, only Rh. dianthi and probably Rh. coffeae are brachypterous. They are easily separated because the latter species is extremely hirsute and has 5- to 7-segmented antennae, whereas the present species only has sparse setae and 10-segmented antennae.

Figures

FIGURE 6. Rhizoecus dianthi Green. Adult male. Where A = hair-like seta; B = fleshy seta; C = loculate pore, and D = simple pore. For other labels, see under Materials and methods: conventions.