Scale insects at Lake Ohau

RECENTLY, botanist Dr Peter Johnson found native scale insects encrusting stems of the native plant Muehlenbeckia axillaris growing as mats on the gravel shore of Lake Ohau.

The scale insects, encased within a hard resinous test, belong to the family Margarodidae and the genus Ultracoelostoma, of which there are three described species. The lower illustrations show the long curved anal tubes that protrude from the tests and through which honeydew is excreted. (Honeydew in native forests is a valuable resource, vital for some native birds at certain times of the year).

Because females and nymphs of the genus

Ultracoelostoma are enclosed within a hard shell, rather than being freeliving, they are globular and almost spherical, rather than flattened and lozengeshaped, as are the nonenclosed freeliving margarodid scale insects.

Identification is difficult, and is based on the shape of minute pores and hairs visible only on cleared flattened specimens mounted on microscope slides and examined at high magnification through a compound microscope.

The individual shown here is an adult female nymph, 2.6mm long. Male margarodids are fully winged, fly, and look very unlike the larviform females. Although very similar to the beech honeydew scale, Ultracoelostoma assimile, it seems to differ in the shape of its antennae as well as in other features from the three described species. Since none of these have been recorded as feeding on Muehlenbeckia axillaris, it may be a new species.

Muehlenbeckia axillaris from Lake Ohau, with encrusting scale insects on stems. Lower illustrations show the long curved anal tubes that excrete honeydew. Inset shows the underside of the globular pink scale insect removed from test. Note: antennae, six legs, long thin central stylets of feeding tube.