Rhizoecus cacticans (Hambleton)

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 : 18-21

Rhizoecus cacticans (Hambleton)

( Fig. 4 )

Ripersiella cacticans Hambleton, 1946: 64 .

Rhizoecus cacticans (Hambleton) ; Ferris, 1953: 432.

Material examined. U.S.A., Maryland, Prince Georges Co., Bowie, no date, Ferocactus latispinus (Cactaceae) , no collector ( USNM): 2/ 4♂♂ in fair condition but several rather distorted.

Mounted material: apterous; very small, total body length about 840 µm, greatest width about 250 µm; antennae 10 segmented, rather long, much more than half total body length; most antennal flagellar segments "bottleshaped", with both hair-like setae (hs) and fleshy setae (fs), but these difficult to separate; antennal setae mainly in whorls; body with few setae, all hs, fine and mainly 10–12 µm long; loculate pores (lp) with mainly 5 loculi, each about 6–7 µm wide. Legs well developed; trochanter with 3 pairs of campaniform pores and a strongly developed Y-shaped sclerotisation; tarsal digitules (tdgt) possibly slightly capitate. Aedeagus (aed) with a broad apex.

Head: greatest width about 120 µm; with 8 or 9 pairs of hs dorsal head setae (dhs) distributed along full length of head; loculate pores absent but with a pair of simple pores present anteriorly; genal setae (gs) absent; with 2 pairs of simple eyes, subequal in size, each 23–25 µm wide; ocular sclerite (ocs) not apparently differentiated; without any sign of ventral midcranial ridge (vmcr) or lateral arms of midcranial ridge (lmcr); with 4 or 5 pairs of ventral head setae (vhs), longest about 15–17 µm long; preocular ridge (procr) restricted dorsally to a short ridge extending medially over dorsal simple eye; ventrally, procr as per diagnosis.

Antennae: 10 segmented; length about 570 µm long (ratio of total body length to antennal length 1:0.68). Scape (scp): 36 µm long, 33–35 µm wide, with 4 hs. Pedicel (pdc): 50–53 µm long, 28–30 µm wide; with 0 or 1 fs, 6–8 hs + a campaniform pore. Segments III–X all about 20–22 µm wide at widest point; segments III & IV broadest distally but segments V–IX all "bottle-shaped" narrowing abruptly about 2/3rds along length to form a narrow "neck" about 8 µm wide; lengths of segments (µm): III 53–57; IV 44–46; V 63–65; VI 63–67; VII 59–63; VIII 60– 68; IX 63–68, and X 66–70; longest setae about 38–40 µm long; approximate number of setae per segment: III 5–8 fs + 5 hs; IV 5–10 fs + 4 or 5 hs; V–VII 11–16 fs + 1–5 hs; VIII & IX 15–18 fs, 0 or 1 hs + 1 short antennal bristle (ab), and X 17–20 setae + 3 ab; long hs not clearly differentiated from fs; setae on segments II–IX mainly in whorls.

Thorax. Prothorax: with a slight narrowing between head and prothorax; segment not noticeably swollen laterally; hs and a few lp distributed in a narrow band across segment, probably representing anterior propleural (apl 1 s) and median pronotal (mpns) setae; also with a pair of setae, 1 lp and a simple pore in position of pronotal ridge setae (prn 1 s) and another pair of setae possibly representing post-tergital setae (pts). Sternum (stn 1) with 2 pairs of lp in position of prosternal setae (stn 1 s) and a pair of lp + simple pores in position of anteprosternal setae (astn 1 s); antemesospiracular setae (am 2 s) represented by a group of 3 or 4 pairs of hs which extend laterally and fuse with posterior propleural setae (ppl 1 s) and lp.

Mesothorax: unsclerotised. Dorsum with 2 narrow bands of hs; ventrally with a small group of setae (possibly postmesospiracular setae (pm 2 s)) anterior to furca, plus a few setae, lp and simple pores associated with each mesothoracic spiracle. Mesothoracic spiracle (sp 2): width of peritreme about 12µm. Furca (f) small but normally developed.

Metathorax: dorsally with a narrow band of hs + a few lp and simple pores extending across full width of segment, representing metatergal setae (mts) and dorsospiracular setae (dss); ventral part of metapleural ridge (plr 3) short but well-sclerotised; metepisternum and metepimeron absent. Metathoracic spiracle (sp 3): width of peritreme about 12–13 µm, with 1 associated lp. Metasternum (stn 3) with a small group of setae + an lp anterior to each metacoxa.

Wings and hamulohalteres (h) absent.

Legs: metathoracic legs longest. Coxae (cx): I 76–78; II 76–79; III 68–70 µm long; coxa III with about 8 hs. Trochanter (tr) + femur (fm): I 150–160; II 135–140; III 150–152 µm long; trochanter III with about 5 hs; each trochanter with 3 pairs of roundly oval sensoria and with strong, sclerotised Y-shaped ridges; long trochanter seta not differentiated but seta in this position about 11 µm long; femur III with about 5–8 hs. Tibia (ti): I 135–144; II 125– 138; III 155–165 µm; tibia III with a total of 16–19 setae, mainly hs, becoming spur-like distally; all tibiae with 2 apical spurs (tibs); length of longest 22 µm. Tarsi (ta) 2 segmented, proximal segment very short and ring-like; length of both segments combined: I 73–75; II 66–68; III 70–72 µm long (ratio of length of tibia III to length of tarsus III 1:0.44); tarsus III with 15 or 16 setae, mainly spur-like; tarsal spurs not differentiated; tarsal campaniform pore present; tarsal digitules (tdgt) represented by a pair of long, possibly capitate, setae, subequal to length of claw. Claws (c) long and narrow, almost straight, with a hint of a small denticle; length: III 23–25 µm; claw digitules (cdt) setose, each about 12–13 µm long.

Abdomen: segments I–VIII: tergites (at) and sternites (as) only detectable on segments VI–VIII; pleurites on VIII present, otherwise absent. Caudal extension (ce) of segment VII absent, that on VIII rounded. Loculate pores (lp) absent ventrally but 1 or 2 present on each side pleurally and with 1 medio-laterally on dorsum of all segments apart from segments VII & VIII, which have a group of 2–4 on each side; setae present in a single line around segments I–VII, not apparently divided into dorsal pleural and ventral setae, with about 24 hs around each segment. Segment VIII without a pair of glandular pouches, but each caudal extension with a rather longer pleural seta about 30 µm long; tergite VIII with 1 pair of hs dorsal abdominal setae (ads) medially (+ 2 or 3 lp on each side); sternite without setae or pores.

Genital segment: penial sheath (ps) large and bulbous, almost as broad as abdominal segment VIII ventrally; dorsally with a well-developed finger-like ridge; proximal half rather quadrate, narrowing to a finger-like distal half; ventrally, penial sheath is divided and appears to extend internally as far as segment VII; length from anterior margin to apex about 155–165 µm, width at widest point 105–110 µm; finger-like extension about 40 µm wide, with a sharp upturned apex; with a wide anus dorsally (width about 16–18 µm) at anterior end and with 3 or 4 longish setae on each side, each about 11–14 µm long. Laterally with 2 or 3 setae, each about 12 µm long. Ventrally, ps with a broad slit-like opening ventrally through which aedeagus emerges; borders of opening quite heavily sclerotised, without setae. Aedeagus (aed) strongly curved, perhaps 100 µm long, with parallel sides when viewed dorsally, widening at both ends, distal end rather shovel-like; anteriorly, aedeagus bends ventrally and fuses with a short sclerotised basal rod (bra). Apex of penial sheath possibly without sensilla.

Comment. The adult males of Rh. cacticans are typical rhizoecine males, differing from those of other species seen here in having the following combination of character states: (i) tarsal digitules probably capitate, (ii) antennae long, with some segments bottle-shaped and most setae appearing to be in whorls, (iii) trochanter with 3 pairs of campaniform pores; (iv) trochanter with strong Y-shaped sclerotisations; (v) aedeagus broadening at apex, and (vi) shape and structure of the penial sheath, particularly the ventral internal extension.

Figures

FIGURE 4. Rhizoecus cacticans (Hambleton). Adult male. Where C = loculate pore; D = simple pore; K = distal end of posterior leg, and H = dorsal view of aedeagus. For other labels, see under Materials and methods: conventions.