Scaptococcus occultans von Ellenrieder & Watson
Ellenrieder, Natalia Von & Watson, Gillian W., 2019, A revision of the mealybug genus Scaptococcus McKenzie (Hemiptera: Coccomorpha: Pseudococcidae), with descriptions of the adult male and female of Scaptococcus occultans sp. n. from the southwestern United States, and the male of S. milleri McKenzie, Zootaxa 4554 (2), pp. 386-400: 392-399
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|Scaptococcus occultans von Ellenrieder & Watson|
Etymology. We name this species occultans (present active participle of Latin ‘occulto’-which means to conceal, hide) in reference to its cryptic habit in the crown of its host, and its existence having remained unrecognised for many years.
Type material. Holotype GoogleMaps adult ♀: U.S.A., California, Riverside County, sand dunes near Palm Desert, 38 th Avenue GoogleMaps and Washington Street GoogleMaps (33° 46'23'' N, 116° 18'14'' W, 34 m. a.s.l.), on Brassica tournefortii , 31.iii.2011, R. Waterworth leg. [CSCA]. Paratypes: 177 ♀♀ (154 adults, 23 immatures), 5 adult ♂♂. U.S.A.: Arizona : 1 adult ♀, intercepted at Vidal Inspection Station , roadside, on unknown weed, 3.ii.2005, Brown leg. [ CSCA, PDR1300006]. California: Inyo County : 1 adult ♀, Bishop, on Parosela (now Dalea) sp., 8.viii.1973, E.L. Paddock leg. [ CSCA]; Kern County : 11 ♀♀ (9 adults, 2 immatures), Monolith, on roots of wild mustard, 20.viii.2002, J.F. & D.R. Miller leg. [ USNM]; Lassen County : 16 ♀♀ (15 adults, 1 immature), 3 ♂♂, Susanville, on side of road, on Tribulus terrestris crowns, 4.ix.2009, B. Villegas leg. [ CSCA, PDR1560941] ; 8 adult ♀♀, same data but on Hypericum perforatum stem/ root junction, 2.xi.2011, B. Villegas, M. Pitcairn & C. Gibbs leg. [ CSCA]; Mono County : 7 adult ♀♀, Chalfant Valley , on Tribulus terrestris , 28.viii.1987, R.J. Gill leg. [ CSCA]; Monterey County : 7 ♀♀ (5 adults, 2 immatures), Greenfield, on unknown host, 19.vii.2004, Waltwood leg. [ CSCA, PDR 1402557]; Riverside County : 4 ♀♀ (3 adults, 1 immature), same data as holotype [ CSCA] GoogleMaps ; 26 ♀♀ (22 adults, 4 immatures), Lake Elsinore , on wild mustard roots, 22.vii.1991, E. Reeves & J. Holt leg. [ CSCA] ; 9 ♀♀ (8 adults, 1 immature), same data but 1.5 miles west of El Cariso , 11.vii.1991, E. Reeves leg. [ CSCA]; San Bernardino County : 9 ♀♀ (7 adults, 2 immatures), Colton, on Salsola sp., 16.vii.1991, R. Lampman leg. [ CSCA] ; 9 ♀♀ (5 adults, 4 immatures), Victorville, The Narrows, on Salsola sp. roots, 14.x.1979, S. Kuba leg. [ CSCA] ; 20 ♀♀ (18 adults, 2 immatures), Barstow, on Atriplex sp., 11.ix.1978, E.L. Paddock leg. [ CSCA] ; 1 adult ♀, San Bernardino, on Tribulus terrestris , 27.x.1969, E. L. Paddock & G. Nash leg. [ CSCA] ; 6 ♀♀ (5 adults, 1 immature), Oro Grande, on Tribulus terrestris , 13.viii.1972, Lounsbury leg. [ CSCA]; San Diego County : 6 adult ♀♀, National City, on Bassia sp., 24.viii.1972, E.L. Paddock et al. leg [ CSCA]; Santa Barbara County : 2 adult ♀♀, Los Alamos, on mustard, 1.viii.2006, H. Scheck & S. Bryant leg. [ CSCA, PDR 1281967]. New Mexico: Bernalillo County : 1 adult ♀, Albuquerque, on foliage of Tribulus terrestris , 22.ix.1995, P. E. Boldt & T.O. Robbins leg. [ USNM]. Nevada: Washoe County : 34 ♀♀ (29 adults, 5 immatures), 2 ♂♂, Reno, on Asteraceae , 21.viii.1993, J. Muran leg. [ CSCA]. Texas: El Paso County : 1 adult ♀, El Paso, on tumbleweed, 1.v.1992, D. Riley leg. [ USNM] .
Description of adult female. Macroscopic appearance. Adult female body oval and rotund, brownish orange to maroon-brown, enclosed in a cover of felted white wax ( Figs 3 View FIGURE 3 , 4 View FIGURE 4 ).
Slide-mounted characters ( Fig. 5 View FIGURE 5 ). Body of adult female oval, becoming larger and more rotund with age, 2.2 ± 0.7 [2.2] (1.1–3.0) mm long, maximum width (at metathorax) 1.6 ± 0.7 [0.6] (0.7–2.6) mm. Anal lobes slightly developed (in younger females) to absent (in older females), each with an apical seta 155 ± 10  (129–166) µm long. Antenna 268 ± 13.2  (239–286) µm long, with 9 segments. Legs well developed, hind tibia 161 ± 9  (141–175) µm long, hind femur 156 ± 14  (131–175) µm long, hind trochanter + femur 217 ± 16  (189–238) µm long, hind tibia + tarsus 246 ± 11  (224–263) µm long; claw well developed, 27 ± 2  (24– 29) µm long, bearing a small denticle. Ratio of lengths of hind tibia + tarsus to hind trochanter + femur 1: 0.9 ± 0.1 [1: 0.8] (1: 0.8–1: 0.9). Ratio of lengths of hind tibia to tarsus 1: 0.5 ± 0.1 [1: 0.5] (1: 0.5–1: 0.6). Dorsal surface of hind tibia distally with 20–40 [25–35] translucent pores, and dorsal surface of hind femur with 4–30  translucent pores. Labium 137 ± 10  (117–146) µm long; clypeolabral shield 158 ± 16  (136–195) µm long; ratio of lengths of labium to clypeolabral shield 1: 1.2 ± 0.1 [1: 1.0] (1: 1.0–1: 1.3). Circulus present between SIII and SIV, hour-glass-shaped to only slightly constricted at midlength, to oval, divided by intersegmental line, 127 ± 29  (83–170) µm wide. In 13% of specimens, a second circulus is present on SII, between SII and SIII, or on SIV, oval to rounded and 9–88  µm wide and, in one specimen, a third circulus is present on SIV, rounded and 34 µm wide. Anterior and posterior ostioles moderately developed. Anal ring 70 ± 6  (58–78) µm in diameter, with a double band of cellular pores, bearing six setae, each seta 58 ± 12  (44–87) µm long.
Dorsum. Slender flagellate setae of two lengths: shorter setae each about 10 µm long; longer setae each about 24–63 µm long. Modified oral collar tubular ducts, with inner half of outer duct strongly sclerotized, present in rows on head, thorax and abdomen. Multilocular pores present on thorax, and in rows on SI–V and SVII, absent from head and SVIII, and present only marginally on SVI. Quinquelocular pores present in medial and submedial areas of thorax. Discoidal pores, each slightly smaller than a trilocular pore, scattered and scarce. Trilocular pores evenly distributed except absent from segmental folds. Cerarii absent.
Venter. Setae flagellate. Anal lobe seta 155 ± 10 (129–166) µm long. Modified oral collar tubular ducts present on head, thorax and abdomen. Multilocular pores each 8.5 µm in diameter, present on head near mouthparts, and numerous on thorax and all abdominal segments. Quinquelocular pores present on head around mouthparts, in medial and submedial areas of thorax and on anterior abdominal segments. Trilocular pores evenly distributed except absent from segmental lines and around coxal bases. Discoidal pores as on dorsum, scarce.
Nymphs. In first-instar nymphs the antenna is 6-segmented, and 7-segmented in second- and third-instar female nymphs. All three nymphal instars share with the adult female the presence of anterior and posterior ostioles, a small plantar denticle on the claw, trilocular pores, quinquelocular pores, a circulus and an anal ring with two rows of cellular pores. Modified oral collar tubular ducts were not detected in first-instar nymphs but are present in second- and third-instar female nymphs. Besides lacking a vulva, all nymphs differ from the adult female by lacking multilocular pores.
Diagnosis. The adult female of Scaptococcus occultans shares with S. californicus and S. milleri the presence of a denticle on each claw, modified oral collar tubular ducts with the inner half of the outer duct sclerotized, multilocular pores, quinquelocular pores, and the absence of cerarii. It is superficially most similar to that of S. milleri , in that both have at least one circulus, dorsal modified oral collar tubular ducts, dorsal multilocular pores and dorsal quinquelocular pores, and cellular pores on the anal ring. Adult females of S. occultans can be distinguished from those of both S. californicus and S. milleri by their unmodified legs, with the prothoracic tibia + tarsus longer than the femur (legs short and stout in S. californicus and S. milleri , with prothoracic tibia + tarsus shorter than femur), and less prominent claw denticles, and additionally from S. milleri by the presence of numerous dorsal modified oral collar tubular ducts, quinquelocular pores and multilocular pores arranged in bands across the thoracic and abdominal segments (in S. milleri there are only a few dorsal modified oral collar tubular ducts, quinquelocular and multilocular pores, mostly on the posterior abdominal segments).
Female nymphs of all three instars of S. occultans can be distinguished from those of the other two Scaptococcus species by their unmodified prothoracic legs, with the tibia + tarsus longer than the femur (tibia + tarsus stout and shorter than femur in S. californicus and S. milleri ), smaller claw denticles, and the unmodified anal ring, with cellular pores present in two rows (in S. californicus and S. milleri , the cellular pores are absent or in a single row).
Description of adult male (based on 5 specimens). Slide-mounted characters ( Fig. 6 View FIGURE 6 ). Body of adult male elongate oval, 1,286 ± 163 (1,010–1,440) µm long, maximum width of mesothorax 357 ± 28 (325–390) µm; fleshy setae entirely absent; all setae hair-like (flagellate with acute apices longer setae proportionally slightly thicker than shorter ones); discoidal pores and multilocular pores present, the latter mostly each with 5 loculi, but a few with 4. Antenna length between half and almost two-thirds of body length. Male macropterous, with wings each 1.2 ± 0.1 (1.04–1.23) times as long as total body length and 0.32 ± 0.5 (0.28–0.35) as wide as long.
Head. Width across genae 190 ± 29.4 (146–219) µm. Each side of head with 9–12 dorsal setae and 2 or 3 genal setae, 0 or 1 multilocular pore, and 0 or 1 discoidal pore near each scape. Ventral head setae form a group between ventral eye and ocellus and base of antenna, numbering 7–9 on each side, accompanied by 0 or 1 multilocular and 0 or 1 discoidal pore on each side. Simple eyes rounded, numbering 2 pairs; dorsal eyes each placed approximately postero-laterally to ventral simple eyes, each 39 ± 3.4 (34–44) µm in diameter, ventral eyes 36.5 ± 2.8 (34–44) µm in diameter. Ocular sclerites weakly sclerotized. Ocelli pronounced, situated laterally, each 28 ± 4.7 (24–34) µm in diameter, located between preocular and post-ocular ridges. Dorsal arm of midcranial ridge extending to about level of posterior margin of dorsal eyes. Preocular ridge well developed, extending medio-dorsally from anterior margin of dorsal simple eyes. Post-ocular ridge well developed, extending ventrally from posterior to each dorsal simple eye antero-laterally past each ocellus and extending postero-laterally to near position of mouth. Interocular ridge not detected. A short extension of the postocular ridge goes around each ocellus. Preoral ridge weakly developed. Cranial apophysis not detected. Ventral mid-cranial ridge short.
Antenna. Ten segmented and filiform; 849 ± 131 (708–986) µm long, 0.7 ± 0.1 (0.52–0.73) of total body length. Scape 47 ± 2.7 (44–49) µm long, with 2 or 3 setae. Pedicel 60 ± 7 (49–68) µm long, with 6–10 setae. Lengths of segments III–X (µm): III, 124 ± 21 (102–151); IV, 104 ± 28 (73–136); V, 100 ± 17 (78–119); VI, 99 ± 22 (73–122); VII, 86 ± 14 (73–102); VIII, 79 ± 11 (66–92); IX, 73 ± 10 (61–83); X, 78 ± 8 (68–88). Approximate number of setae on each of segments III–X: III 16–21; IV 1 8–21; V 14–16; VI 14–18; VII 13–17; VIII 11–15; IX 10–13; X 15–17; VIII and IX with 1 ventral antennal bristle, X with 2 subapical antennal bristles and 1–3 subapical sensilla basiconica; capitate setae absent.
Thorax. Prothorax. Pronotal ridge heavily sclerotized; pronotal sclerite represented by a subtriangular sclerotization dorsolaterally. Each side of pronotal medial area with 0 or 1 seta, 1 or 2 multilocular pores, and 0 or 1 discoidal pore; pronotal lateral area with 0 or 1 seta, 1 or 2 multilocular pores, and 0 or 1 discoidal pore; pronotal ante-spiracular area with 0 or 1 seta, 1 multilocular pore, and 1 discoidal pore; post-tergite indistinct. Ventrally ante-spiracular area with 0 or 1 seta, 0 or 1 multilocular pore, and 1–3 discoidal pores. Sternum triangular, with well-developed transverse prosternal ridge; without prosternal setae and pores. Anteprosternal area with 0 or 1 seta, 0 or 1 multilocular pore, and 0 or 1 discoidal pore.
Mesothorax. Prescutum oval, sclerotized, prescutal ridge well developed, prescutal suture distinct, with 2 or 3 prescutal setae on each side. Scutum sclerotized, with about 2–6 scutal setae and 0 or 1 discoidal pore on each side; prealar ridge and triangular plate well developed. Scutellum sub-rectangular, sclerotized, with 1 or 2 scutellar setae on each side; anterior and posterior pronotal wing processes well separated. Basisternum bounded anteriorly by a marginal ridge, posteriorly by strong precoxal ridges, median ridge absent, with 5–7 basisternal setae on each side, mainly along anterior and medial area. Lateropleurite narrow, mesepisternum and mesepimeron distinct; furca well developed, arms divergent and extending about two thirds of the way to marginal ridge anteriorly. Subepisternal ridge long and well developed. Postalare without setae. Each side posterior to mesospiracle with 1–3 postmesospiracular setae, 1–4 multilocular pores and 1–5 discoidal pores. Tegula present, with 3 or 4 tegular setae.
Metathorax. Metapostnotal sclerite and metapleural ridge weakly developed; precoxal ridge well developed and metasternal apophyses distinct. Metepisternum and metepimeron weakly sclerotized; postmetaspiracular area with 1 seta, 1 or 2 multilocular pores, and 1 discoidal pore. Metasternum membranous, anterior metasternal area with, on each side, 1–3 setae, 1–5 anterior multilocular pores, 1–3 anterior discoidal pores, posterior metasternal area with 0 or 1 seta, 0 or 1 posterior multilocular pore, and 0 or 1 posterior discoidal pore.
Wings. Hyaline, each 1,072 ± 178 (830–1,260) µm long and 370 ± 127 (280–460) µm wide. Ratio of length to width 1: 0.3 ± 0.1 (1: 0.3–1: 0.4); ratio of total body length to wing length 1: 0.9 ± 0.1 (1: 0.8–1: 1.0); alar lobe well developed and each wing with 2 or 3 alar setae and 2 circular sensoria. Hamulohalteres 98 ± 16 (78–117) µm long, with an apical hamulus 75 ± 7 (68–83) µm long.
Legs. Prothoracic femur slender, 222 ± 28 (175–248) µm long, with maximum width of 34 ± 3 (31–39) µm, and ratio of maximum width to length 1: 10.0 ± 0.8 (1: 8.7–1: 10.7). Metathoracic legs (III) longest; hind femur 209 ± 29 (160–234) µm; hind tibia 318 ± 45 (238–346) µm; hind tarsus 126 ± 11 (107–136) µm; hind tarsal claw 32 ± 2 (29–34) µm. Ratio of hind femur length to hind tibia length 1: 1.5 ± 0.1 (1: 1.5–1: 1.6); ratio of hind tibia length to hind tarsus length 1: 0.4 ± 0.1 (1: 0.4–1: 0.5). Setae numbering: coxa I 8–11, II 8– 14, III 13–15; trochanter I 4–8, II 4–8, III 5–8; femur I 26–38, II 22–35, III 36 –42; tibia I 40 –54, II 45 –52, III 58 –60; tarsus I 22–30, II 26–30, III 30–44. Each trochanter with 3 campaniform sensilla arranged in a triangle medially on each side. Tibia each with 2 apical spurs. Tarsi each 2 segmented, tarsal digitules not detected. Claws each with a small denticle, spine-like with an unusually narrow base and acute tip ( Fig. 6 View FIGURE 6 ); claw digitules acute.
Abdomen. SI–VI: membranous, each segment with dorsal abdominal setae totaling: SI 4 or 5; SII 6 or 7; SIII 4–6; SIV 7; SV 7 or 8; SVI 5–8; dorsal and ventral abdominal pleural setae and pores on each side numbering: SI 0–3 setae + 3–9 multilocular pores + 0–2 discoidal pores; SII 3 setae + 2–4 multilocular pores + 1 or 2 discoidal pores; SIII 2–5 setae + 1–5 multilocular pores + 1–3 discoidal pores; SIV 2–4 setae + 1–3 multilocular pores + 1–3 discoidal pores; SV 4 or 5 setae + 0–3 multilocular pores + 0–2 discoidal pores; SVI 4 or 5 setae + 0–2 multilocular pores + 0 or 1 discoidal pore. Ventral abdominal setae numbering: SII 2; SIII 3 or 4; SIV 6–8; SV 6–8; SVI 4–6. With a pair of distinct ostioles present laterally between segments SVI and VII. SVII–VIII: membranous except for sclerotized medial tergal area on SVIII; dorsal setae on SVII numbering 5, on SVIII 0–2; ventral setae on SVII numbering 5, on SVIII 0. Glandular pouches shallow, pouches on SVII each with 6–36 multilocular pores spreading out around pouch, 0–3 discoidal pores, and 2 long glandular pouch setae, each 218 ± 2 (214–219) µm long; pouches on SVIII each with 18–54 multilocular pores spreading out around pouch, 0–6 discoidal pores, and 2 long glandular pouch setae, each 217 ± 8 (204–224) µm long.
Genital segments. Penial sheath (comprising SIX and style) with a transverse constriction at about two-thirds of its length, 112 ± 11 (95–122) µm long, 68 ± 7 (60–73) µm wide across basal ridge, ratio of penial sheath length to width 1: 0.6 ± 0.1 (1: 0.5–1: 0.6). Dorsum of style with 2 or 3 setae posterior to constriction on each side. Ventrally, style approximately triangular, gradually narrowing to a narrowly rounded apex; anterior basal ridge on SIX well developed ventrally; penial sheath lacking lateral processes on either side of ventral opening; with 2 or 3 ventral setae on each side of SIX, 4 or 5 smaller ventral setae on each side of style and 3–6 sensilla near its apex. Basal rod distinct. Aedeagus 94 ± 3 (90–97) µm long, approximately parallel sided, ending in a pointed tip that does not extend posteriorly beyond end of penial sheath; in lateral view, bent ventrally at about 45° at base. Anus not detected.
Diagnosis. As in the females, the prothoracic femur is stouter in the adult males of Scaptococcus milleri than in S. occultans . They also share with their females the presence of a denticle on each claw. The prothoracic denticle has a wide base and right-angled tip in the adult male of S. milleri , whereas it is spine-like, smaller and slender, with an unusually narrow base and acute tip in the adult male of S. occultans . Meso- and metathoracic denticles also appear spine-like in S. milleri , but not as small and slender as in S. occultans . The adult males further differ by the presence of small, slightly sclerotized abdominal tergites laterally on SII–VII in S. milleri , which are absent in S. occultans , and by a larger number of dorsal and ventral abdominal setae on SII–V in S. milleri than in S. occultans .
In having 2 pairs of glandular pouches and discoidal pores, the males of Scaptococcus are typical members of the Phenacoccinae. Males of four other phenacoccine genera have been described, differing mostly in the distribution of the multilocular pores and other small features; the spine-like denticles observed here in the meso- and metathoracic claws of S. milleri and in all the claws of S. occultans seem to be unique for this genus.
Biology. Scaptococcus occultans occurs on the crown and roots of its hosts. The adult female secretes a cover of felted white wax, which encloses both her body and the eggs ( Figs 3 View FIGURE 3 , 4 View FIGURE 4 ).
Hosts. Amaranthaceae : Bassia sp., Salsola sp.; Asteraceae ; Brassicaceae : Brassica tournefortii ; Chenopodiaceae : Atriplex sp.; Fabaceae : Dalea sp.; Hypericaceae : Hypericum perforatum ; Zygophyllaceae : Tribulus terrestris .
Distribution. Arizona; California (Inyo, Kern, Lassen, Mono, Monterey, Riverside, San Bernardino, San Diego and Santa Barbara Counties); New Mexico (Bernalillo County); Nevada (Washoe County) and Texas (El Paso County) ( Fig. 1 View FIGURE 1 ).
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