Promyrmococcus dilli Williams

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 : 72-75

Promyrmococcus dilli Williams

( Fig. 27 ).

Material examined. Paratypes: Sabah, Kinabalu, Poring, in nest of Dolichodorus marchwitzi (Formicidae) , 18.vii.1991, M. Dill ( BMNH): 9/9ad ♂♂ (mainly good).

Mounted material. Small, total body length about 1.3–1.5 mm; apterous. Antennae about half total body length, with long setae (probably fleshy setae (fs), each 1.5–2.0 times longer than width of antennal segments); body with many hair-like (hs) setae, some on each segment extremely long, 450–770 µm long; fleshy setae (fs) apparently absent on body. Trilocular pores absent; simple pores few. Head more or less without ridges or sclerites. Simple eyes (se) absent; ocelli (o) present. Mouthparts reduced and non-functional but present. Legs well developed, each with a 2-segmented tarsus (ta) and without tibial or tarsal spurs; tarsal digitules (tdgt) knobbed. Circulus often present between abdominal segments III and IV. Ostioles (os) present, both anteriorly and posteriorly, with strongly sclerotised margins. Glandular pouches (gp) absent but with a group of setae plus a few 5-locular pores in this position. Anus (an) near apex of penial sheath, under abdominal segment IX. Ventrally, penial sheath (ps) with a pair of lobes medially.

Head. Short, total length perhaps 130 µm and about 320 µm wide behind ocelli. All ridges and sclerites missing apart from (i) a very short preocular ridge (procr) ventrally and (ii) a small slerite between it and each ocellus, probably representing a much reduced ocular sclerite (ocs) – both procr and ocs apparently absent on 1 specimen. Head covered both dorsally and ventrally with long, fine hs, each 20–60+ µm long. With 1 pair of longer seta on anterior margin and 2 pairs of even larger setae dorsally. Simple eyes absent; ocelli (o) positioned laterally, each 33–40 µm wide. Cranial apophysis not detected or perhaps represented by a small sclerotisation near posterior margin on venter. Mouthparts much reduced, without stylets, present between procoxae; clypeolabral shield about 50–60 µm long; labium about 35–40 µm long with 7–9 pairs of setae.

Antennae. Eight- or 9-segmented and filiform; each 700–825 µm long (ratio to total body length 1:0.54). Setae all flagellate but perhaps of 2 sizes, larger each 75–100 µm long, possibly representing fs, and shorter setae each 40 µm long and perhaps hs. Scape (scp) approximately square, 57–80 µm long, 70–83 µm wide, with many setae but these most abundant dorsally. Pedicel (pdc) 62–75 µm long, 54–58 µm wide, without concentric ridges; with numerous setae + a campaniform pore. Segments III on 8-segmented antennae usually with some sign of a pseudoarticulation but clearly separate from segment IV on 9-segmented antennae. Segments III–( VIII) IX all about 50–55 µm wide, and each with numerous setae; lengths (9-segmented) (µm): III 70–75; IV 50–55; V 85– 105; VI 100–120; VII 100–120; VIII 100–120 and IX 70–83; combined lengths of III and IV on 8-segmented antennae 125–133. Segments VII and VIII each with a large bristle and segment IX with 3 large bristles. Capitate setae (cs) absent; sensilla basiconica (sb) not detected.

Thorax. All 3 segments very similar with bands of hs extending around each segment; loculate pores absent but a few simple pores (ssp) present. All segments each with 1 pair of very large setae and a pair of smaller setae near margin and a pair of large setae submedially. Spiracles: width of peritreme: anterior 23–26 µm wide, posterior 30–32 µm wide. Prothorax with a pair of large ostioles (os), each with sclerotised margins.

Wings. Apterous.

Legs. Metathoracic legs longest, all segments with many hs. Lengths (µm): coxae (cx): I 140–150; II 135– 150; III 128–150. Trochanter (tr) + femur (fm): I 330–370; II 340–373; III 360–395; all trochanter with 2 campaniform pores on anterior margin and 3 pores arranged in a triangle medially on posterior margin; without strong, sclerotised Y-shaped ridges for articulation with femur; long trochanter seta not differentiated. Tibia (ti): I 245– 265; II 255–275; III 295–310; all tibia without spur-like setae (tibs). Tarsi (ta) all 2 segmented; length of both segments combined: I 100–105; II 90–100; III 112–115 (ratio of tibia III length to tarsus III length 1: 0.38); all tarsus III without tarsal spurs (tars); tarsal campaniform pore present; tarsal digitules (tdgt) longer than claw, capitate. Claws (c) each quite broad basally, subequal in length to width of tarsus, without a denticle; length ( III) 40–43 µm; claw digitules (cdt) short and fine but with a blunt apex.

Abdomen. Segments I–VII: tergites (at) and sternites (as) unsclerotised and without obvious oval membranous areas in inter-segmental areas. Caudal extension on segment VII absent. Without loculate pores. Each segment with a band of numerous hs extending round segment, plus a pair of very large setae submedially and another pair submarginally along with a pair of intermediate-sized setae. Segment VI with a pair of large ostioles, with sclerotised margins, and with 2 pairs of larger setae on ventral margin.

Segments VIII & IX. Segment VIII clearly sclerotised throughout; most setae much as on anterior segments; caudal extension (ce VIII) very rounded with 5–7 hs very large and intermediate-sized pleural setae. Glandular pouches (gp) absent but with a small group of 1–7 quinquelocular pores in this position and a rather variable-sized group of setae but usually with 2 very large setae in this position also. Segment IX represented by a squarish area of sclerotisation above penial sheath, with anus at posterior end; width of anus 33–40 µm wide. With 2 pairs of setae just posterior to anus.

Genital segments. Penial sheath (ps) lying mainly beneath abdominal segment VIII; fairly short, a little longer than broad, narrowing sharply at posterior end into a narrow finger-like extension; total length 230–250 µm, greatest width 155–165 µm, apical finger (style) about 50 µm long. Basal ridge (brps) indented medially; lateral processes of penial sheath distinct, each with 4–7 short setae; also with a group of 5 or 6 short hs laterally. Basal rod (bra) distinct, about 33 µm long, extending anteriorly to about half-way to basal ridge. Aedeagus (aed) parallel sided, broadest at proximal end, extending almost to end of penial sheath; aed 200–230 µm long. Apex of ps with a large group of sensory pores (psp); no penial sheath setae detected.

Comment. Although apterous and apparently morphologically rather similar to adult males of Xenococcinae , the adult male of P. dilli has the following character states which place it in the Pseudococcidae (character states of males of Rhizoecidae in brackets): (i) both anterior and posterior ostioles present (ostioles absent); (ii) some specimens with what appears to be a sclerotised ocular sclerite ventrally on the head (sclerite absent); (iii) ocelli (absent): (iv) a circulus (absent); (v) glandular pouch absent but loculate pores present in this position (absent); (vi) abdominal tergite IX distinct (absent or not differentiated); (vii) anal opening at posterior end of tergite IX (anus near anterior margin of penial sheath), and (viii) ventral opening on penial sheath with a pair of well-developed lateral processes (absent). Thus, although the adult male of P. dilli appears to be missing many of the features used above to diagnose adult males of Pseudococcidae (postocular ridge distinct; postoccipital ridge present; dorsal and ventral midcranial ridges usually well developed; pronotal ridge and pronotal sclerite present; propleural ridge generally well developed as a proepisternum + cervical sclerite, extending anteriorly to reach head; and glandular pouches usually present on abdominal segment VIII), the presence of the above eight character states immediately places this male in the Pseudococcidae . It is here assumed that the loss of the other features is secondary, due to their trophobiotic relationship with ants, thus making them morphologically convergent with the myrmecophilous Rhizoecidae .

This description differs slightly from that of Williams (2002). In this study, the following character states were found: (i) a probable ocular sclerite (not illustrated in Williams); (ii) antennal bristles present only on apical 3 segments (on apical 4 segments in Williams); (iii) circulus not present on all specimens (present); (iv) tarsus 2 segmented (illustrated as 1 segmented); (v) locular pores of glandular pouch present (not mentioned or illustrated), and (vi) lateral processes on ventral surface of penial sheath well developed (less well developed).

As indicated above, Williams (2002) placed the Allomyrmococcini in the Pseudococcinae based on adult female characters. The structure of the penial sheath of P. dilli is also very similar to that of Planococcus glaucus described above ( Fig. 24 ), placing it close to the tribe Pseudococcini (see also the penial sheaths of Trionymus newsteadi , Nipaecoccus nipae , Octococcus africanus (Brain) , and Planococcus citri in Afifi (1968)).

Figures

FIGURE 24. Paracoccus glaucus (Maskell). Adult male. Where C = loculate pores; D = simple pore; J = dorsal view of posterior end of abdomen; K1 = tibio-tarsal articulation; K2 = claw; L = ventral view of posterior end of abdomen, and N = side view of penial sheath of P. marginatus Williams (latter modified after Miller and Miller, 2002). For other labels, see under Materials and methods: conventions.

FIGURE 27. Promyrmococcus dilli Williams. Main drawing modified after Williams, 2002. Adult male. Where C = loculate pore of glandular pouch; D = simple pore; J = dorsal view of posterior end of abdomen; K = distal end of posterior leg; L = ventral view of posterior end of abdomen; P1 = anterior view of trochanter showing 2 campaniform pores; P2 = posterior view of trochanter showing 3 campaniform pores; Q = apical 2 antennal segments; R = 2 views of circulus, and T = ventral view of head. For other labels, see under Materials and methods: conventions.