Giant native scale insect identified

Otago Museum

EARLIER this month, Suus Claessen photographed a very large soft oblongoval mealybug on the trunk of a southern beech tree in Catlins rainforest park, rightly describing it as ‘‘pink and gorgeous’’.

About 15mm long, it had a fine dusting of white wax. The symmetrical elliptical shape indicates it had only recently moulted into the adult stage.

This was a very young adult female of the giant native scale insect Coelostomidia zealandica, of the family Margarodidae. It occurs in native forest throughout New Zealand.

Called ‘‘the native giant scale insect’’, and by some trampers ‘‘the big jujube scale insect’’, C. zealandica is sometimes noticed on the floor of native forest during summer and autumn. Found in both North and South Islands, it occurs in the bark of host plants and walks on tree trunks and on the forest floor.

During summer, its feeding stages cause tree trunks to be covered in honeydew, along with the secretions of other scale insects. Many native nectarfeeding forest birds depend on this honeydew at certain times.

The adult male has welldeveloped wings, antennae, legs, and compound eyes. Its body is dark pinkish purple with clear purplish wings. It is a beautiful fragile shortlived creature that locates the female with its antennae. The male undergoes complete metamorphosis, but the female does not. In addition to two nymphal stages, the male has a prepupa, and a true pupal stage within an elongated cocoon.

Unlike the male, the female undergoes only two nymphal stages before changing directly into an adult. She does not go through a pupal stage and therefore resembles a sexually mature nymph. Consequently, she is an example of neoteny: ‘‘the retention of some juvenile characteristics in the sexually mature adult’’. This male/ female difference occurs in all of the eleven families of scale insects present in New Zealand and in further families overseas.

The family Margarodidae contains some of the largest of all scale insects, some Australian species reaching a length of over 35mm.

Adult male Coelostomidia wairoensis, a related native giant scale insect, to show the large difference between the sexes in these insects. Left: Female giant native scale insectCoelostomidia zealandica, found recently on a beech tree in Catlins rainforest park.