Macadamia cultivation has grown significantly in South Africa over the past few decades, and this country has become one of the largest producers of macadamia nuts worldwide.

In April 2017, heavy infestations of a previously unobserved scale insect were noticed on macadamia trees in the Barberton Valley in Mpumalanga. Specimens of the pest were diagnosed at the National Collection of Insects, Biosystematics Division, as the macadamia felted coccid, Eriococcus ironsidei Williams (Hemiptera: Eriococcidae). It is not clear how this species was introduced to South Africa, but it may have been accidentally brought in on propagative plant material.

This scale insect species is native to Australia, and occurs only on macadamia trees. Damage caused by this insect to macadamias in Queensland was reported in 1970, and the pest was described as a new species, Eriococcus ironsidei, in 1973.

By 2005, this species had become established in Hawaii, after being accidentally introduced to that island region. Although it has been observed to occur only sporadically in Hawaii, when infestations become high it causes severe damage to macadamia trees and extensive dieback of branches. In Australia, this pest has been found to be capable of causing flower drop and reduced nut set.

Eriococcus ironsidei on macadamia leaf, showing general appearance. Photo: Dr. Colleen Hepburn.

The macadamia felted coccid can be recognised by the felt-like appearance of its protective scale cover. The adult female scale is about 1.5mm long, dirty white or pale yellow in colour, with a raised circular opening at the posterior end. The scale cover of the male is white and is smaller, about 1.0 mm long. The female may be observed by turning its protective scale over with fine forceps; important features are its orange colour and the pair of pointed, conical, elongate lobes at the end of the abdomen.

The impact of this newly-arrived pest on the local macadamia industry may take some years to assess, if it is indeed a sporadic problem. However, it is definitely an important quarantine organism as it lives attached to its host plant and can easily be transported on exported and imported produce.

Care should be taken to prevent the movement of infested plant material in macadamia producing areas, in order to reduce the risk of spreading the pest amongst orchards. Containing or controlling this scale insect in restricted areas should be aided by the mainly sedentary lifestyle of this species. –ARC-PHP newsletter