Asian cycad scale

The cycad scale is a tiny, orange, sap-sucking bug that lives under a white or translucent shelter (scale) it constructs from anal secretions to protect it from weather and enemies. The scales of females are less than 2 millimetres long and highly variable in form. They tend to be pear-shaped but can be circular, oblong, or irregular in shape when scales are crowded together. They often remained attached to the cycad surface, even after the bug has died. The scales of male are long and narrow and smaller. They have a grooved surface.

The underside of this frond shows a scatter of female scales alongside the much smaller males. Photo: John A. Davidson, Univ. Md, College Pk, Bugwood.org

This species is very difficult to distinguish from similar scales, and it is their dense white infestations that should be looked for, in combination with sick and dying cycads. They should be looked for on cultivated cycads, and on wild cycads growing near houses.   

The sago palm (Cycas revoluta), more properly called the sago cycad, is often grown in Australian parks and gardens and is highly susceptible. Plants under early attack reveal their plight by first showing small yellow spots on the upper surface of their fronds. As the infestation progresses fronds turn yellowish then brown and dry. 

This cycad has brown dessicated fronds, a withering green frond, and frond stalks densely coated in cycad scales. Photo: F.W. Howard, University of Florida, Bugwood.org

This cycad is dying from scale attack. Photo: Florida Division of Plant Industry, Bugwood.org

Those who aren’t familiar with cycads may confuse them with young palms, since both have fronds. The leathery leaves of cycads are much thicker and stiffer than those of palms. The trunks are very thick for the height of the plant. Many cycads, including sago palm, have fronds on which each leaflet ends in a spine. Its leaflets are rigid and only about 4 millimetres wide.

Sago palms can suffer dieback on the tips of their leaflets, which can turn whitish, but this looks very different from scale attack, which is not directed at leaf tips.

A female scale can be seen here beneath her semi-transparent cover. Beside her are two male scales. Photo: Jeffrey W Lotz, Florida Department of Agriculture and Consumer Services, Bugwood.org | CC BY 3.0

Females are 1.2-1.6 millimetres long. Males are only 0.5 to 0.6 millimetres long.

The scales at first congregate mainly on the undersides of fronds, but when they reach extreme numbers they attach to the stalks of fronds, the cones and seeds, to upper frond surfaces and to roots up to 60 centimetres underground. Heavy infestations lead to multiple layers of live and dead scales forming a waxy white ‘crust’ on the frond surface at densities of hundreds per square centimetre. A cycad can end up looking like it is dusted in snow. It may die within months or even weeks of the first scale arriving.

The false oleander scale (Pseudaulacaspis cockerelli) and hibiscus snow scale (Pinnaspis strachani) sometimes feed on cycads, though they are not cycad specialists and do not reach extreme numbers. The false oleander scale is more likely to feed on the upper side of fronds than beneath them. It is yellow rather than orange but the difference in colour is not pronounced and not a reliable way to distinguish the two

This scale likes a subtropical or tropical climate and is unlikely to do well south of Sydney.

Think you’ve found Asian cycad scale?

If you find them phone 1800 900 090 and ask for the office of Australia’s Chief Environmental Biosecurity Officer. Contact us as well via our online form.

This sap-sucking scale has caused mass deaths of wild and cultivated cycads since it spread around the world from its native Thailand with the cycad trade. Cycad species in Taiwan and Guam are now endangered following its arrival. It multiplies so rapidly, achieving dense populations, it can kill a cycad grove within a year of arriving. The IUCN considers it the ‘single most important threat to natural cycad populations’.

The Australian government foolishly allows the importation of fresh cycad foliage for sale in floral arrangements, and the scale could enter on these. It has been intercepted in many countries on imported cycads or cycad foliage, including New Zealand.

Australia is a global centre for native cycads, with 70 species, the vast majority of which have such small distributions they are inherently vulnerable to any new enemy. Australia has 28 species of Cycas, the main genus afflicted by the scale overseas. The country has 38 species of Macrozamia, a genus confined to Australia that is sometimes cultivated abroad, hence an overseas report that a southern Queensland species, M. lucida, is particularly susceptible to the scale. Australia has two species of Bowenia and this genus is also susceptible. Some of Australia’s cycads grow in places that could be too dry for the bug, or too remote for it to reach, but large numbers of species should be considered vulnerable, including some that are already listed as endangered, such as M. lomandroides.

Cycads are such popular garden plants that the scale is a major concern for horticulture as well. The main cycad cultivated in Australia, the sago palm, is often killed by the scale in gardens overseas. One nursery in Taiwan lost 100 000 sago palms in a year.