Emerging plant pests - spiraling* whitefly

Trevor Lambkin, Indooroopilly Research Station, Indooroopilly, Brisbane

*The American spelling of 'spiraling' using only one 'l' is here retained and adopted because of the Hawaiians (USDA) original naming and spelling of the pest's common name.

Spiraling whitefly (Aleurodicus dispersus ) is a pest of many horticultural crops, as well as an extensive range of ornamentals and shade trees. It originated in the Caribbean region of Central America, and spread rapidly through the Pacific after gaining establishment in Hawaii in 1978. Not a fly at all, but a relative of the bugs, spiraling whitefly derives its name from the characteristic egg spirals that the adult whitefly lays on foliage and fruit. Without its natural predators it has assumed major pest status. It is now established on coastal mainland Queensland in areas from Mackay north.

Damage is mainly caused by the sap-sucking immature and adult whiteflies that feed on the underside of the foliage. Heavily infested plants soon develop a black sooty appearance from mould growing on the sugary secretions that the whitefly immatures excrete. This in combination with leaf damage reduces the plant's ability to photosynthesise and results in loss of plant production.Whiteflies can multiply at a great rate, producing thousands of individuals on a single plant, when natural biological agents are not present. Very high populations may result in defoliation, loss of production and in severe cases, death of the plant.

Control

A biological control agent (a parasitoid) was originally established in Torres Strait in 1992 by DPI&F entomologists from Brisbane. This parasitoid is a small, almost microscopic orange-coloured wasp that is host specific to the pest and has already successfully controlled pest populations in Torres Strait and Cape York Peninsula. Parasitoid stocks that have originated from this first establishment are now being used by DPI&F  to successfully control mainland populations of spiraling whitefly, in particular those established in the northern tropics. Insecticidal control is not recommended as overseas experience indicates that spraying with insecticides has little long-term impact on the pest and may exacerbate the pest problem by destroying the biocontrol agents.

Host range

Spiraling whitefly attacks a broad range of horticultural plants including banana, citrus, papaya, mango, custard apple, guava, tomato, capsicum, eggplant and also many ornamental species, shade trees and weed species. The pest has been recorded infesting over 100 plant species in Torres Strait and in 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 overseas countries. Because spiraling whitefly is tropical in origin and can also  breed in sub-tropical conditions, its host range could well be much more extensive, as there are many subtropical and temperate horticultural and ornamental plants that are still untried against spiraling whitefly attack.

Detection and identification

Life history of the spiraling whitefly

Spiraling whitefly adults are small (2.0mm long), white and moth-like in appearance and mode of flight. When heavy infestations occur, the adult whitefly and immatures 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 immatures.

This secretion can lead to a heavy coating of black sooty mould. Mixed in with the heavy 'wax' are the spiraling 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. The adults are generally active during calm, still times of the day, eg. dawn and dusk, when they can be seen flying in large circular patterns around the host plant. Normally adults can be induced to fly by shaking the infested plant, after which they then quickly resettle.

Spiraling whitefly bears a superficial resemblance to a closely related species, 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 wattle. At times, it occurs in banana plantations in North Queensland but causes no damage . Coconut whitefly adults are indistinguishable by eye from adults of spiraling whitefly but the immatures are noticeably different to a trained observer. The waxing on the immatures of coconut whitefly are coiled and much longer, and the immatures have twelve compound pores which are larger than the eight compound pores of spiraling whitefly immatures. Eggs of coconut whitefly are laid on similar flocculent trails as spiraling whitefly but the trails are not in spiral shapes.

Life history

Eggs (0.3mm long) are diamond shaped, almost microscopic, and are embedded in the silken spirals produced by the female. The egg hatches into an active crawler stage of about the same size as the egg. This stage crawls out over the undersides of the host's leaves and then transforms into an inert, sedentary stage that sucks nutrients from the leaves. This nymphal stage (0.5mm-1.06mm long) has no visible legs and grows progressively through a series of moults (instars), each instar producing more and 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 weather. The female whitefly (which is identical to the male) can lay large numbers of eggs.

Further information

Early recognition of this pest in Australia is crucial to its control. Suspected infestations should be reported to your closest Plant Health Officer.

Further information is available from the DPI&F Customer Service Centre. Queensland residents can contact the Customer Service Centre by phoning 13 25 23 for the cost of a local call. Other Australian residents can phone the Customer Service Centre on +61 7 3404 6999.

Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.

Last reviewed 28 April 2006