RHIZOECIDAE Williams, 1969

Hodgson, Chris, 2020, A review of neococcid scale insects (Hemiptera: Sternorrhyncha: Coccomorpha) based on the morphology of the adult males, Zootaxa 4765 (1), pp. 1-264 : 22-25

RHIZOECIDAE Williams, 1969

Rhizoecini Williams 1969, 335.

Rhizoecinae Williams 1969 , 335; Koteja 1974b, 45; Tang 1992, 42.

Rhizoecidae Williams ; Hodgson, 2012, 4.

Type genus: Rhizoecus Künkel d’Herculais.

Type species: Rhizoecus falcifer Künkel d’Herculais 1878 , 164 by monotypy.

Introduction. The taxa with the hypogaeic and myrmecophilous mealybugs have, until recently, been included in the Pseudococcidae as the subfamily Rhizoecinae . However, a phylogenetic study based on DNA sequences and including representatives from all five pseudococcid subfamilies, found that the Rhizoecinae (represented by 4 species in 3 genera) formed a monophyletic group sister to the remaining pseudococcids ( Downie & Gullan 2004). Later, based on adult male characters only, Hodgson and Foldi (2005) found that Rhizoecus formed a separate clade with Pityococcus , sister to the Pseudococcidae . Since then, also largely based on the morphology of the adult males, Hodgson (2012) reviewed the relationships of the Pseudococcidae and the hypogaeic and myrmecophilous mealybugs, and concluded that the rhizoecine mealybugs formed a separate family from the Pseudococcidae ( Rhizoecidae Williams ) and that this family included two subfamilies, Rhizoecinae Williams and Xenococcinae Tang. A more recent study ( Hodgson & Hardy 2013), also based on adult male morphology, also found the Rhizoecidae to be a separate clade, sister to the Pseudococcidae . However, Danzig and Gavrilov-Zimin (2014) did not accept this and argued that: (a) the hypogaeic mealybugs belonged within the Pseudococcidae , possibly sister to Mirococcopsis Borchesenius , and that (b) the myrmecophilous Xenococcinae were unrelated to the Pseudococcidae and might be closest to the Margarodidae s.l. Danzig and Gavrilov-Zimin therefore raised the Xenococcinae to family status, Xenococcidae Tang, although this was without phylogenetic support. Whilst it is still the view of the present author that the Rhizoecidae are sister to the Pseudococcidae , he agrees that the relationships of the Xenococcinae are problematic and that it should be raised to family status. As understood here, the Rhizoecidae contains 16 genera and 214 species ( García Morales et al. 2019).

Family diagnosis based on adult male morphology. Many species apterous but some with brachypterous or fully macropterous adult males. Unless otherwise stated, diagnosis refers to all morphs. Body generally small to minute, cylindrical, somewhat pointed at both ends. Head without ocelli, although two pairs of simple eyes generally present; preocular ridges generally recognisable ventrally although often not strongly developed; postocular ridge absent although a faint line occasionally present marking posterior margin of ocular sclerite; postoccipital ridge absent; dorsal midcranial ridge absent; ventral midcranial ridge poorly developed or absent; base of antennae placed close together near anterior margin of head; number of antennal segments variable, each 3–10 segmented, with fs and hs setae on most segments; capitate setae on antennae generally absent or not differentiated; neck entirely absent. Loculate pores frequently present on head, thorax and/or abdomen. Thorax. Pronotal ridge and pronotal sclerite absent; propleural ridge short, at most only extending anteriorly about half-way to head; apterous species without any mesothoracic sclerotisation. Metaprecoxal ridge absent; leg setae hs or spinose, not fs; each trochanter with 3 round sensoria arranged in a curve or triangle on each side; trochanter often divided by a Y-shaped sclerotisation; tarsi with 2 spurs; tarsi generally clearly 2 segmented, occasionally 1 segmented; tarsal digitules often undifferentiated; claws long and narrow with setose digitule s. Abdomen. Ostioles absent; abdominal segment VIII without glandular pouches and without a group of disc-pores, although 1 or more long setae may be present in this position; abdominal segment IX not apparently differentiated, but position indicated by anal opening found dorsally at anterior end of dorsal ridge on penial sheath; ventral opening of penial sheath often indistinct and never with lateral finger-like processes; penial sheath about as broad as long; penial sheath without a large, U-shaped, sclerotised structure extending anteriorly within abdomen from base of aedeagus (if an obvious internal sclerotisation present, this never as long as penial sheath). Macropterous and brachypterous species also with: scutum without a membranous area; basisternum without a median ridge; alar lobes present on each wing but hamulohalteres absent; alar setae present; alar sensoria present or absent.

Discussion. In his 2012 paper, Hodgson found that the morphology of the adult males of the Rhizoecidae was very variable, particularly in the number of antennal segments, and that male morphology did not entirely support the classification based on the morphology of the adult female of Kozár & Konczné Benedicty (2007). The males of the macropterous rhizoecine mealybugs, Rhizoecus coffeae Laing ( Fig. 2 ), Ripersiella hibisci ( Figs 2 & 3 ) and Rhizoecus dianthae Green ( Fig. 4 ), plus an apterous rhizoecine mealybug, Kissrhizoecus hungaricus Kozár & Konczné Benedicty ( Fig. 5 ), are illustrated here to illustrate the diversity of the family. A key to the described rhizoecine adult males plus descriptions and other illustrations can be found in Hodgson (2012).

Figures

FIGURE 2. Rhizoecus coffeae Laing. Macropterous male. (Rhizoecidae, Rhizoecina). Where A=hair-like seta, B=fleshy seta, C=loculate pores, K=proximal end of metathoracic leg, and Z=mouth tubercle. For abbreviations, see p. 8.

FIGURE 3. Ripersiella hibisci (Kawai & Takagi). Macropterous male. (Rhizoecidae, Ripersiellina). Where A=hair-like seta, B=fleshy seta, C =loculate pores, F=alar sensoria, and K=proximal end of metathoracic leg. For abbreviations, see p. 8.

FIGURE 4. Rhizoecus dianthi Green. Brachypterous male. (Rhizoecidae, Rhizoecina). Where A=hair-like seta, B=fleshy seta, C=loculate pore, D=simple pore, and G=wing microtrichia. For abbreviations, see p. 8.

FIGURE 5. Kissrhizoecus hungaricus Kozár & Konczné Benedicty. Apterous male. (Rhizoecidae, Rhizoecina). WhereA=hairlike seta, B=fleshy seta, C=loculate pore and K=tibio and tarsus. For abbreviations, see p. 8.