XENOCOCCINAE TANG, 1992

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 : 51

SUBFAMILY XENOCOCCINAE TANG, 1992

Xenococcinae Tang, 1992: 42 .

Introduction. The Rhizoecinae (here Rhizoecidae ) were divided into two tribes by Tang (1992) on the basis of the presence ( Rhizoecini — here Rhizoecinae ) or absence ( Xenococcini — here Xenococcinae ) of ostioles on the adult females. However, it is known now that some adult females of Rhizoecinae lack ostioles (e.g. Capitisetella and Pseudorhizoecus ). Nonetheless, in the Rhizoecinae , the third-instar female is a normal feeding instar whereas it has been shown ( Williams, 2004a) that all three genera included in the Xenococcinae have a third-instar pupal (nonfeeding) stage before the fourth-instar (adult) female stage, clearly separating the two subfamilies. In addition, Williams (2004a) showed that, in the adult females of those species where circuli were present, they are flat or bulbous distally in the Rhizoecinae , whereas in the Xenococcinae they are depressed or cup-shaped at the centre of the distal end. Adult females of Xenococcinae also lack tubular ducts, pores and tubular cerores, all of which occur on most Rhizoecinae . Additionally, Schneider and LaPolla (2011) showed that all Xenococcinae are obligate trophobionts with ants of Acropyga Roger. The latter are considered to feed primarily on the honeydew produced by the xenococcine scale insects and the alate ant queen is known to carry one of the xenococcines in its mandibles during her maiden flight, so that the colony she founds has a food source. The most recent key to the adult females in this subfamily is in Schneider and LaPolla (2011).

In their cladistic study of the tribe Xenococcini based on adult female morphology, Schneider and LaPolla (2011) obtained a polytomy with four clades and one ungrouped species, one clade equating to Neochavesia , one to Xenococcus and three to Eumyrmococcus , which therefore may not be monophyletic. These clades were found to be related to their geographical distributions, with Neochavesia restricted to the Neotropics, Xenococcus to the Indo- Australian Region, the scorpioides- clade (three species, including the ungrouped E. williams Kozár & Konczné Benedicty ) of Eumyrmococcus to Africa and the Palaearctic, and the smithii -clade to Asia, the Pacific and Australia. However, Schneider and LaPolla (2011) only used three representative species of pseudococcine and rhizoecine genera ( Geococcus , Rhizoecus and Phenacoccus ) as their outgroups but there was support for three of the clades with posterior probability scores of 100, although Bootstrap values were all low (≤76) and there was no support for E. williamsi grouping with the other two species of the E. scorpioides -group.

Subfamily diagnosis based on adult male morphology. Unmounted material: all trophobionts of ants of the genus Acropyga . Mounted material: apterous; minute to small, total body length about 100–1350 µm; body more or less round in cross-section; either broadest in head region, generally either narrowing gradually posteriorly or narrowing abruptly in abdominal segment II or III ( Eumyrmococcus and Neochavesia ), or broadest in thoracic region and narrowing gradually posterior to about segment V ( X. acropygae ); antennae each long or short, on anterior margin of head; body setae generally abundant (sparse on E. sarawakensis , E. smithii and minute on X. acropygae ), all hs; loculate pores (lp) mainly absent (trilocular pores present on Neochavesia caldasiae ); other pores absent. Legs mainly well developed, trochanter and femur fused on E. sarawakensis and X. acropygae , and extremely short on X. acropygae . Head: rounded, unsclerotised, without any sign of a constriction between head and prothorax. Setal distribution highly variable, either possibly absent ( X. acropygae ), very sparse ( E. sarawakensis ) or frequent to dense (other species). All head ridges absent; lp absent (apart from on N. caldasiae ). Simple eyes and ocelli absent. Cranial apophysis absent. Antennae: 1 segmented on X. acropygae with some long apical setae; otherwise mainly well developed and 2–5 segmented (poorly developed on E. sarawakensis and E. smithii ); scapes quite wide apart, but well differentiated. Pedicel possibly never differentiated. Flagellar segments either fused into 1 large apical segment ( E. taylori and Neochavesia nr. trinidadensis ), ring-like ( E. sarawakensis and E. smithii ) or each segment reasonably elongate; with hs setae; apex with hs setae, and antennal bristles. Thoracic segments: barely differentiated from head and rest of body, each segment rather similar; without sclerites (well sclerotised laterally and dorsally on X. acropygae ). Setal distribution and setal size variable. Loculate pores only present on prothorax of N. caldasiae . Pleural ridges well developed (short on X. acropygae ). Prosternum (stn 1) unsclerotised; sternal apophyses absent. Spiracles (sp 2, sp 3) generally quite large and well developed. Wings: entirely apterous. Legs: subequal in length. Trochanter + femur fused on E. sarawakensis and X. acropygae ; each trochanter with a pair of campaniform pores on each side; without a strong, Y-shaped sclerotised ridge between trochanter and femur; long trochanter seta undifferentiated. Setae all hs (and minute on X. acropygae ). Tibia (ti) with tibial spurs differentiated only on N. nr. trinidadensis . Tarsi (ta) 1 segmented; tarsal spurs not differentiated; tarsal digitules (tdgt) probably present and setose. Claws (c) generally long and slightly curved but stouter on some Neochavesia species ; without a denticle; claw digitules (cdt) either short and setose or absent but spinose on X. acropygae . Abdomen: posteriormost segments narrowing to a blunt apex on X. acropygae ; segments variously modified, probably for transport by ants; segments II–VIII narrow or narrowing posteriorly; without sclerites. Caudal extensions on segments VII and VIII absent, represented by large lobes on Neochavesia species and small lobes on X. acropygae . Loculate pores absent. Setae sparse on E. sarawakensis , E. smithii and X. acropygae , otherwise frequent to abundant, particularly on segment VIII. Ostioles absent. Segment VIII with some long setae on all but E. sarawakensis and E. smithii ; glandular pouches absent. Genital segment: penial sheath (ps) quite long, extending anteriorly into abdomen on all but E. taylori (uncertain on E. smithii ), forming a deep U-shaped structure, to which basal rod and aedeagus are attached ventrally; apex of various shapes but narrow; with few or no setae. Anus (a) located dorsally above anterior end of penial sheath. Ventrally, with a median slit-like opening through which aedeagus emerges. Aedeagus (aed) quite long and narrow, often longer than penial sheath, generally with a pointed apex (blunt on E. sarawakensis ), with a strong basal rod (bra).