Common name

Ground pearls or margarodids

Field characters

Body large, up to 5 mm or more, generally rotund, but some species elongate oval; legs (especially front pair) fossorial, enlarged and adapted for digging; occurring in soil or sand; feeding on roots of host; usually without wax secretion except some species produce a filamentous ovisac.

Validation characters

Body large; front legs greatly enlarged for digging , often with some leg segments fused; abdominal spiracles normally present, sometimes absent; thoracic spiracles usually with pores in atrium; anal opening generally not obvious; without cicatrices; usually without mouthparts; tarsus with more than 1 campaniform sensilla; forming a cyst.

Notes

The family Margarodidae, as here treated for the ground pearl groups only, is relatively uniform in adult female morphology but is surprisingly diverse in structural details of the first instars and cysts (Jakubski 1965). This diversity is so dramatic that Jakubski divided the group into 2 families, 5 subfamilies, and 7 tribes. There appears to be considerable merit in at least part of his classification scheme although the rank of the units requires careful examination. Margarodidae Cockerell was first used as a family by Enderlein (1914).

Distribution

Ground pearls occur in all zoogeographic regions.

Hosts

Margarodids occur on a diverse array of plant hosts from annual grasses to perennial shrubs and perhaps even trees. They generally occur on the rootlet and roots of the host, but early in the year some species as first instars infest the leaves of graminaceous hosts.

Life history

Because of the subterranean habit of the species in this family, little detailed information is available on their biology. Two species of economic importance have been studied. Porphyrophora tritici (Bodenheimer) is a pest of wheat. According to Duran (1971) it has a single generation per year and overwinters as eggs in the ovisac in soil. In December the crawlers hatch, emerge from the soil, and crawl into the leaf sheaths of the grass where they feed for 30 to 45 days. The first instar enlarges, reenters the soil, and molts to the cyst stage in early April. This instar feeds on the roots of the host until late May or early June when adult females appear. After moving through the soil for several days at a depth of 3 or 4 cm, the female begins forming an egg sac and lays eggs. Porphyrophora polonica (Linnaeus) has a similar life history. One difference is that adult females climb to the top of vegetation waiting for adult males. During the cyst stage, there are multiple molts (up to 12). Sphaeraspis vitis (Philippi) also has a similar biology, but can survive for years in the cyst stage. Jakubski (1965) described a single generation each year, but González (1983) discussed generations taking multiple years.

Important references

Duran 1971; González 1983; Hodgson and Foldi 2006; Jakubski 1965; Morrison 1928; Vahedi & Hodgson 2007.

Diversity

Click here for a check list of all margarodid genera and species.