December 2001. Pictures of the Egyptian fluted scale, Icerya aegyptiaca were sent from Palau for confirmation. The infestation is on croton bushes badly injured by twine trimmers (or “green machines,” as they are known here) – 1-2 cm diameter stems completely stripped of bark for a length of 5-10 cm – see 2 attached
pictures. Weeds around the shrubs were removed and compost applied, then the stems were painted with
Tangle-trap to stop the ants.
[Trimmer injury is very common in Palau, It occurs on coconut trees with boles smaller near the ground because of root damage. Often infestations of insects: whiteflies on guava, aphids on hot pepper (capsicum) and scales on croton occur on the trimmer-damaged plants whereas the healthy, uninjured trees and shrubs nearby are without infestations.]
This scale is common in the Darwin area, and attacks a wide range of plants. Two species of ants are often associated with this scale – green ant, Oecophyllya smaragdina and a species of Crematogaster (as seen in the background of the attached photo. The latter is a tree nesting species and is not a problem. However, the presence of green ants may prevent parasites and predators being effective, and these ants may possibly also farm the scales.
Scale insects cannot be identified with 100% certainty, unless they are prepared as microscope slide mounts for proper taxonomic identification.
This scale is sometimes called breadfruit mealybug because it can for damaging infestations on that host-plant. Its successful biological control in Kiribati by Rhodolia pumila is discussed by Waterhouse & Norris (1987) Biological control: Pacific prospects. 454 pp. Inkata Press, Melbourne.
Other possible biological control agents might be the Dipteran parasite, Cryptochaetum grandicorne (which attacks I aegyptiaca at levels of up to 90% in India and Pakistan), or the Eulophid wasp Tetrastichus sp. (known from Pakistan). This is briefly discussed in Watson, Ooi & Girling (1995) Insects on plants in the Maldives and their management. 124 pp. International Institute of Biological Control, Ascot, Berks, UK. (p. 37-39).
Sometimes the control of ants, e.g. by judicial pruning and use of sticky bands (e.g. of Tanglefoot) around the trunk, is enough to reduce the scale population significantly.