MARGARODIDAE Cockerell

Watson, Gillian W., 2022, Towards identification of the scale insects (Hemiptera: Coccomorpha) of continental Africa: 2. Checklists and keys to six archaeococcoid families, Zootaxa 5105 (3), pp. 301-356 : 305-308

Family MARGARODIDAE Cockerell

Common names: Ground pearls or margarodids.

Background: In the early literature (e.g., Morrison 1928; Borchsenius 1960), the ancient family Margarodidae sensu lato contained species showing an enormous range of morphological and biological variation. Koteja (1974) first proposed breaking the Margarodidae sensu lato into six families, based on the structure of the labium, whereas Hodgson and Foldi (2006) subsequently recognized 11 families, based on male morphology. The name Margarodidae sensu stricto is now applied to a family group of ten genera containing 109 described species ( Foldi 2005a; Miller et al. 2014; García Morales et al. 2016). The species are all highly adapted for life underground, spending part of the life cycle as a dormant cyst in the soil (a “ground pearl”) (de Klerk et al. 1983; Gavrilov-Zimin 2018). The cyst stage can live for multiple years and is an adaptation to survive long periods of drought when the host plant cannot grow ( Miller et al. 2014). Adult females have relatively uniform morphology, but the immature stages show a dramatic diversity of structural details. Historically, some species of Porphyrophora were used as sources of valuable red dyes for textiles ( Vahedi and Hodgson 2007). The Margarodidae of Africa have not been well studied and there may well be more, undescribed species still to be found.

Appearance in life: Normally found in soil or sand, usually on roots of annual grasses or perennial shrubs or trees, but early in the growing season crawlers sometimes found infesting grass leaves. Body of adult female large, length up to 5.0 mm or more, generally rotund, but some species elongate oval. Mouthparts normally absent; anterior legs enlarged for digging (fossorial); usually without wax secretions apart from a filamentous wax ovisac produced in some species. Cyst of immature female ovoid, amber yellow to dark brown, sometimes appearing iridescent or metallic, surface often textured.

Identification: The best specimens for identification are young adult females just after the final moult, before the body has become distended with developing eggs. Adult female ( Fig. 2 ) large, up to 5.0 mm long or more, normally without mouthparts; anal opening not obvious. Forelegs greatly enlarged for digging through soil, often with some leg segments fused; each tarsus with more than one campaniform sensilla. Abdominal spiracles usually present (occasionally absent); thoracic spiracles each usually with pores in atrium. Cicatrices absent in adult female, occasionally present in cyst stage (de Klerk et al. 1983; Miller et al. 2014).

Economic importance: In South Africa, Margarodes capensis , M. prieskaensis and M. vredendalensis are becoming increasingly important as pests on grapevines (de Klerk et al. 1983). Infestation causes patches of vines to die, and vineyards can be destroyed. Ground-pearl feeding devitalizes the vines through sap depletion and possibly by injection of salivary toxins. Infested vines gradually decline; shoots become progressively thinner and shorter and leaves sparser, and after five or six years the vine may die (de Klerk et al. 1983). In South America, Margarodes vitis is a serious pest of grapevines ( González 1983). Unlike an infestation of grapevine phylloxera ( Daktulosphaira vitifoliae , Hemiptera: Aphidomorpha : Phylloxeridae ), in ground pearl infeststions no root galls are formed (de Klerk et al. 1983). In the Middle East, Porphyrophora tritici (Bodenheimer) is a pest of wheat ( Vahedi 2001).

Biology: The underground habit of margarodids makes them difficult to study so their biology is not well known. In at least some species, the life cycle can take several years and includes at least one immature instar that forms a dormant cyst to survive adverse conditions like drought ( Fig. 3 ). In some species, the only time spent above ground is a brief period as adults for mating, whereas some other species reproduce parthenogenetically. Margarodids occur on various hosts, from annual grasses to perennial shrubs and perhaps even trees, usually feeding on the roots, but early in the year the crawlers of some species infest the leaf sheaths of grasses. Porphyrophora tritici , a pest of wheat in the Middle East, has one generation annually and overwinters as eggs in an ovisac underground. On hatching, the crawlers climb into grass leaf sheaths and feed there for 30‒45 days; then they return to the soil and moult into the cyst stage, which feeds on grass roots for 30‒45 days. During this stage there are up to 12 moults before the adult female emerges to mate above ground, then returning to the soil to produce an ovisac and eggs at a depth of 3‒4 cm ( Durán 1971; Vahedi 2001).

Checklist and distributions of Margarodidae in continental Africa (5 genera, 25 species)

Dimargarodes tanganyicus Jakubski : Tanzania

Margarodes aurelianus (Hall) : Sudan

Margarodes cadeti Foldi : Burkina Faso

Margarodes capensis (Giard) : South Africa

Margarodes congolensis Jakubski : Democratic Republic of the Congo

Margarodes greeni Brain : South Africa

Margarodes newsteadi (Brain) : South Africa

Margarodes peringueyi (Brain) : South Africa

Margarodes prieskaensis Jakubski : Namibia, South Africa

Margarodes ruber (Brain) : South Africa

Margarodes salisburiensis (Hall) : Zimbabwe

Margarodes trimeni Giard : South Africa

Margarodes upingtonensis de Klerk : South Africa

Margarodes vredendalensis de Klerk : South Africa

Margarodes williamsi (Jakubski) : Ghana

Margarodesia desmieri Foldi : Ivory Coast

Neomargarodes aethiopicus Silvestri : Eritrea

Neomargarodes aristidae Borchsenius : Algeria, Libya

Neomargarodes erythrocephalus Green : Algeria, Sudan, Western Sahara

Neomargarodes hyparrheniae Hall : Zimbabwe

Neomargarodes pilosus (Jakubski) : South Africa

Neomargarodes trabuti Marchal : Algeria, Tunisia

Porphyrophora buxtoni (Newstead) : Algeria

Porphyrophora erythraea Silvestri : Eritrea

Porphyrophora hirsutissima (Hall) : Egypt, Morocco

Porphyrophora libica Silvestri : Libya

Porphyrophora parieli (Vayssière) : Morocco

Porphyrophora rhodesiensis Hall : Zimbabwe

Key to genera of Margarodidae in continental Africa, adult females

1(0) Prothoracic leg with claw base developed into a distinct, sclerotised heel. Abdominal spiracles numbering 8 pairs......................................................................................... Neomargarodes ( Fig. 4 )

- Prothoracic leg with claw base not developed into a distinct, sclerotised heel. Abdominal spiracles numbering 0‒7 pairs... 2

2(1) Antennal segments without setae except for a group on apical segment. Abdominal spiracles numbering 0‒2 pairs, situated on anterior abdominal segments if present.................................................. Porphyrophora ( Fig. 5 )

- Antennal segments each bearing at least 1 whorl of setae. Abdominal spiracles numbering 2‒6 pairs................... 3

3(2) Abdominal spiracles numbering 7 pairs..................................................... Margarodes ( Fig. 6 )

- Abdominal spiracles numbering 2 or 6 pairs................................................................ 4

4(3) Abdominal spiracles numbering 6 pairs, all same size. Body margin with pleural extensions bearing spines, setae and pores. Venter with distinct groups of spines, setae and pores. Hosts unknown for the African species........ Dimargarodes ( Fig. 2 )

- Abdominal spiracles numbering 2 pairs (on anterior abdominal segments), anteriormost largest. Body margin smooth and with numerous setae, without pleural extensions or spines. Venter with short conical spines, setae and pores but not in distinct groups. On roots of oil palm in Ivory Coast................................................ Margarodesia ( Fig. 7 )

Figures

FIGURE 2. Margarodidae, morphology of adult female; Dimargarodes tanganyicus Jakubski from Vahedi & Hodgson (2007: 32, Fig. 3), reproduced with permission © Trustees of the Natural History Museum, London, U.K.

FIGURE 3. The life cycle of ground pearls (Margarodidae), from Foldi (2005a: 90, Fig. 2), reproduced with permission from Annales de la Société entomologique de France.

FIGURE 4. Neomargarodes trabuti Marchal, adult female, developed from Morrison (1928: 79, Fig. 28).

FIGURE 5. Porphyrophora hirsutissima (Hall), adult female, from Vahedi & Hodgson (2007: 61, Fig. 14), reproduced with permission from the Editor, Journal of Natural History, A: antenna; B: foreleg; C: hind leg.

FIGURE 6. Margarodes prieskaensis, adult female and A: immature cyst stage, developed from de Klerk et al. (1982: 70-71, Figs. 6 and 7) and de Klerk et al. (1983: 135, Fig. 2); reproduced with the authors’ permissions.

FIGURE 7. Margarodesia desmieri Foldi, adult female, from Foldi (2005a: 103, Fig. 10), reproduced with permission from Annales de la Société entomologique de France. A: antenna.