Common name

Palm scales or halimococcids

Field characters

Body normally pyriform, occasionally subcircular or elliptical with the posterior end constricted and protruding. In cross section the body is flattened ventrally and convex dorsally. The adult female, and third-instar female (if present) occur inside a hardened test formed by the adult female. Pieces of the second instar may be incorporated in the test. Most writers suggest that the adult female occurs inside the shed skin of the second instar, but according to Kohler (1987) this is not true. Females remain inside the second instar, produce a test, and the second instar skin ruptures and disintegrates. White wax is not common in most species, but filamentous strands are occasionally present laterally. Specimens usually occur on the leaves of the host and are generally dark brown or black.

Validation characters

Second instar female with anal operculum; tubular ducts divided longitudinally, 8-shaped; antennae 1-segmented; legs absent; without pygidial lobes or plates.

Notes

Some species of Thysanococcus have small plates and enlarged setae on the posterior portion of the body that seem analogous to the lobes of armored scales. Stickney (1934) mentions third-instar females in several but not all species of the family, but Kohler (1987) suggests that Stickney confused the nonexistent third instar with the ruptured ventral surface of the second instar. Halimococcidae Brown and McKenzie was first used as a family by Brown and McKenzie (1962).

Distribution

Palm scales occur in all zoogeographical regions of the world. Click here for a list of genera and species from the Australasian region, Afrotropical region, Nearctic region, Neotropical region, Oriental region, and Palaearctic region. They are most speciose in the Australasian region, and least numerous in the Neotropical area.

Hosts

Halimococcids are most commonly collected on the leaves of palms but also occur on Pandanus.

Life history

Palm scales probably have 3 female instars and 5 male instars. Stickney (1934) described several third instar females, but these may be the partially disintegrated venter of the second instar (Kohler 1987). All species occur within a hardened test and as far as is known, produce eggs. Crawlers escape from the test through the anal operculum which is pushed outward. After shedding to the second instar the derm begins to harden, and become sclerotized. The adult female remains within the shed skin of the second instar and produces a wax test similar to the scale cover of armored scales. The test material eventually causes the second-instar exuviae to rupture on the ventral surface and the cover is primarily made up of waxy material produced by the adult. Development of the adult male through the prepupal and pupal stages occurs within the shed skin of the second instar; no wax test is produced. Kohler suggests that there are multiple generations per year and that the fecundity of individual females may be as low as only 10 eggs.

Important references

Deitz 1979; Ferris 1952; Kohler 1987; Stickney 1934.

Diversity

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