Photo 2. Enlargement of Photo1 showing sub-circular female cashew scales, Pseudaonidia trilobitiformis, and the off-centre skin of the earlier moult.
Cashew scale. It is also known as the trilobite scale.
Pseudaonidia trilobitiformis. It was previously recorded as an Aspidiotus species, and as Pseudaonidia darutyi. [Note, a definitive identification of the scale on citrus from Fiji is awaited. The scale was provisionally identified using photos on orange. It is more usually found on leaves.]
Widespread. Africa, Asia, North, South and Central America, the Caribbean, Europe, Oceania. It is recorded from Australia, Fiji, French Polynesia, New Caledonia, and Vanuatu.
The host range is very wide. It has been recorded on more than 45 plant families. Barringtonia, capsicum, chilli, citrus (many species), coconut, coffee, Ficus (many species), frangipani, mango, woody legumes are hosts, but there are others.
Leaves and more rarely fruits are infested (Photos 1&2). The scale cover of the female is semi-circular, 2.5-3 mm diameter, domed, yellowish-brown, with the side adjacent to the leaf midrib flattened. The remains of the first moult is red-brown, off-centre and clearly visible. The exposed body of the female is wine-red (Photo 3). The male is oval, 1.8mm long, dirty white.
Crawlers are the primary dispersal stage and move to new areas of the plant or are dispersed by wind or animal contact. Mortality due to abiotic factors is high in this stage. Dispersal of eggs, 'crawlers' (nymphs), and adults through transport of infested plant material.
The scale is known as an important pest of cashew, citrus and cocoa.
Look for sub-circular pale or yellow-brown scale covers, each with dark red-brown central or sub-central area, the remains of the original scale.
The parasitic wasp, Habrolepis neocaledonensis, has been recorded in New Caledonia, and the predator ladybird beetle (Coccinellid), Rhyzobius pulchellus, attacks nymphs and adults in Vanuatu and New Caledonia.
Crawlers are more susceptible to insecticides than other stages, but they are very small and difficult to see. There are also overlapping generations, so adults are always present, and this means that several applications of chemicals are necessary to obtain control. Adults are difficult to kill because of their protective scales. (Note dimethoate, once recommended in Pacific island countries, is under suspension in Australia for use on many crops.)
AUTHORS Grahame Jackson & Mani Mua
Information from Diaspididae of the World 2.0 Pseudaonidia trilobitiformis. (https://diaspididae.linnaeus.naturalis.nl/linnaeus_ng/app/views/species/nsr_taxon.php?id=113125&cat=TAB_DESCRIPTION&epi=155); and from Garcia Morales G et al. (2016) ScaleNet: A literature-based model of scale insect biology and systematics. Database. (http://scalenet.info/catalogue/Pseudaonidia%20trilobitiformis/). Photo 3 MAF PLant Health & Environment Laboratory (2011) Trilobite Scale (Pseudaonidia trilobitiformis). PaDIL - (http://www.padil.gov.au).
Produced with support from the Australian Centre for International Agricultural Research under project HORT/2016/18: Responding to emerging pest and disease threats to horticulture in the Pacific islands, implemented by the University of Queensland and the Pacific Community.
This fact sheet is a part of the app Pacific Pests and Pathogens
The mobile application is available from the Google Play Store and Apple iTunes.