Have you seen spiralling whitefly infestations?
Be on the lookout for symptoms and report them to Biosecurity Queensland. Early detection is vital.
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The spiralling whitefly (Aleurodicus dispersus) is a tropical pest to a variety of horticultural crops, ornamental plants and shade trees. It is believed to have originated in the wet tropics of Central and South America, but after gaining establishment in Hawaii in 1978, it spread rapidly through the Pacific. It is now almost pan tropical in distribution, even occurring in some subtropical and temperate countries.
Spiralling whitefly is not actually a fly, but a sap sucking bug, and derives its name from the characteristic egg spirals that the adult whitefly deposits on foliage and fruit. Spiralling whiteflies predominately occur as a winged adult or whitefly stage and a sedentary nymph stage. Without its natural predators, spiralling whitefly can rapidly assume major pest status. It is now established in tropical coastal Queensland from Torres Strait to Gladstone. In addition, it is now known to be in the Darwin region.
Whiteflies feed on the undersides of foliage. Heavily infested plants with very high whitefly populations soon develop a black sooty appearance from mould growing on the sugary secretions that the whiteflies and their nymphs produce. This sooty mould, in combination with leaf damage, reduces the plant's ability to photosynthesise. It also weakens, or in some cases kills the plant. When its natural biological agents are not present, spiralling whiteflies multiply at a rapid rate, producing thousands of individuals on a single plant.
If you see spiralling whitefly symptoms south of Gladstone, report immediately to Biosecurity Queensland.
|What it looks like|
Spiralling whiteflies are small (0.2 mm long), white, and are moth-like in appearance and in their mode of flight. On plants with heavy infestations, whiteflies and their nymphs occur in dense populations on the undersides of the leaves of the host plant. These populations are generally covered in a heavy coating of white, curly 'wax' and a sugary secretion that is produced by the whitefly nymphs.
This secretion often leads to a heavy coating of black sooty mould. Mixed in with the heavy 'wax' are the whitefly eggs that are laid on the silken spirals that the adult females produce. These spirals are more noticeable in initial infestations, low infestations and on the skin of fruits and vegetables.
Spiralling whitefly bears a superficial resemblance to the closely related coconut whitefly that is widely distributed in the Austro-Oriental Region from New Britain to West Malaysia, Solomon Islands and Australia. It occurs in Queensland and is a minor pest of a range of horticultural and ornamental plants including coconut, custard apple, banana and Acacia. It has been recorded in banana plantations in Northern Queensland but is not considered a pest.
Coconut whiteflies are indistinguishable by eye from spiralling whiteflies but the nymphs are noticeably different to a trained observer. The waxing on the nymphs of coconut whitefly is coiled and much longer than the waxing on spiralling whitefly, and coconut whitefly nymphs have 12 compound pores, which are larger than the eight compound pores of spiralling whitefly nymphs. Coconut whiteflies lay their eggs on similar flocculent trails as spiralling whitefly but the trails are not in typical spiral patterns.
|What to look for|
Spiralling whiteflies are generally active during calm, still times of the day (e.g. at dawn and dusk) when they can be seen flying in large circular patterns around host plants. Whiteflies can be induced to fly by shaking the infested plant, after which they quickly resettle.
Eggs (0.3 mm long) are diamond shaped, microscopic, and embedded in the silken spirals produced by the females. Each egg hatches into a tiny active crawler, roughly the same size as the egg. This crawler moves out over the foliage of the host plant and then transforms into an inert, sedentary (nymph) stage that attaches to the underside of the leaves where it sucks nutrients from the leaves. The nymph stage (0.5 mm - 1 mm long) has no visible legs and grows progressively through a series of moults (instars), each instar producing more 'wax' and sugar secretions. The final instar acts as a pupa, out of which the adult whitefly emerges. The time from egg to adult can be less than three weeks in summer, longer in cooler conditions. The female whitefly (which is identical to the male) can lay large numbers of eggs.
Spiralling whitefly infests a broad range of horticultural plants including banana, citrus, papaya, mango, custard apple, guava, tomato, capsicum, eggplant and many ornamental species, shade trees and weeds. It has been recorded on more than 100 plant species in Torres Strait and Cape York Peninsula. Although citrus and mango have not yet been recorded as major hosts in Australia, heavy infestations have occurred on these two species in some countries, particularly after application of insecticides. Because spiralling whitefly is tropical in origin, but can also breed in subtropical conditions, its host range could be much more extensive than what is currently known.
A biological control agent (Encarsia dispersa) was originally established in Torres Strait in 1992 by entomologists from the Department of Agriculture and Fisheries (DAF). This agent is a microscopic, orange-coloured wasp that is host-specific to spiralling whitefly nymphs and has already successfully managed pest populations in Torres Strait and mainland Queensland.
Controlling the pest using insecticides is not recommended. Overseas experience indicates that spraying with insecticides has little long-term impact on the pest and usually exacerbates the problem by destroying the biological control agents and increasing insecticide resistance in whitefly populations.
Lambkin, TA 1996, 'Pest status and control of spiraling whitefly in Queensland', in Department of Primary Industries' Information Series Q196075, p. 59.
Lambkin, TA 1999, 'A host list for Aleurodicus dispersus Russell (Hemiptera: Aleyrodidae) in Australia', Australian Journal of Entomol, vol. 38, pp. 373-376.
Lambkin, TA 2004, 'Successful establishment of Encarsia haitiensis Dozier (Hymenoptera: Aphelinidae) in Torres Strait, Queensland, for the biological control of Aleurodicus dispersus Russell (Hemiptera: Aleyrodidae)', Australian Entomologist, vol. 31, pp. 83-91.