Spiralling whitefly in Australia - what we have learnt

Spiralling whitefly (Aleurodicus dispersus) entered Australia in 1991 via the Torres Strait islands that lie just south of the southern coast of Papua New Guinea. It is now known to occur only in Queensland as far south as Cairns. Since 1992, pest numbers in the region have been significantly reduced due to the action of the introduced hymenopterous parasitoid, Encarsia sp. (? haidensis). Effective reductions in pest numbers occurred within two years after multiple parasitoid releases were made in a given area. The parasitoid was more effective during the wet season and on A. dispersus hosts with flat, broad leaves. The inhibition of pest numbers in the region by Encarsia sp. was aided by Acletoxenus sp. (Diptera: Drosophilidae) and Cryptolaemus affinis (Coleoptera: Coccinehdae). In Torres Strait and Cape York Peninsula, pest numbers were found to be highest during the monsoonal dry season, and the most preferred hosts were guava, sea almond, poinsettia, and acalypha, particularly acalypha varieties with dense growth habits. A. dispersus is capable of dramatic increases in population size. High numbers cause wilting of the host, reduced flowering and dropping of leaves, flowers and fruit. Production losses have been recorded overseas, This damage is caused directly by whitefly nymphs and adults that suck sap, and indirectly by the inhibition of photosynthesis by the covering of leaves with associated sooty mould. Control of the pest in Central America has become difficult in banana plantations where there is a heavy reliance on pesticides. The difficulty in control has been attributed to the effect of terbufos and carbofuran on parasitoid survival, and possible pesticide resistance in the pest. These data indicate that in Australia, potential problems exist for the future control of A. dispersus in irrigated tropical and subtropical agricultural systems, and in cropping systems reliant on pesticide use.