Common name

Xylococcids

Field characters

Body of adult female usually large, often red or brown, with conspicuous legs (legs absent in Xylococcus filiferus) and antennae. Cysts of Xylococculus and Xylococcus located under bark, with a thin wax tube protruding from bark that is attached to anal opening. Adult females and cysts of Stigmacoccus species occur in tests on the branches of the host.

Validation characters

Tarsus (when present) 2 segmented; cicatrices or simple pores normally present; 8 abdominal spiracles; abdominal spiracles usually with associated pores; multilocular pores with more than 5 loculi; mouthparts absent or reduced.

Notes

The composition of this family has not changed dramatically since the definitive classification presented by Morrison (1928). The most important difference is the removal of the Matsucoccidae into a separate family group. This hypothesis is supported by the phylogeny presented by Gullan and Sjaarda (2001). Xylococcidae Pergande was first treated as a family by ZahradnĂ­k (1959a).

Distribution

Xylococculus is recorded from the Nearctic; Xylococcus is from the Palaearctic; Stigmacoccus is from the Nearctic and Neotropical regions; Parakuwania and Baisococcus (fossil) are from the Palaearctic region.

Hosts

Xylococcids are found on trees in the following genera: Alnus, Betula, Calocedrus, Cupressus, Fagus, Inga, Juniperus, Quercus, and Salix.

Life history

A definitive life history study was undertaken on Xylococculus macrocarpae (Coleman) in California (Tait et al. 1990). Females have 4 instars and males have 5. There is a single generation each year. Adult females lay eggs on the foliage in a sac that is formed by the abdomen; no waxy ovisac is produced. Crawlers move to the branches and bole of the tree where they molt twice into legless cysts. In early spring, adults emerge from the cyst and migrate back to the foliage. Second-instar males molt to a legged prepupa that moves to the lower bole and produces a cocoon. Prepupae develop in the cocoon and adult males emerge soon after. This life history differs slightly from those reported for other species. Oguma (1919) suggested that there were 4 female instars and 6 male instars in Xylococcus japonicus Oguma. Florence (1917) indicated that there were 5 male and 5 female instars in X. macrocarpae and Hubbard and Pergande (1898) found 5 female instars and 6 male instars in X. betulae. It has been suggested that the dramatic difference between mobile and settled crawlers might explain some of the discrepancy. Birds are frequently attracted to the large quantities of honedew produced by species of Stigmacoccus (Greenberg et al. 1993).

Important references

Florence 1917; Foldi 1995; Gill 1993; Greenberg, Caballero, and Bichier 1993; Hodgson and Foldi 2006; Hubbard and Pergande 1898; Morrison 1928; Oguma 1919; Tait, Dahlsten, Gill, Doyen 1990.

Diversity

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