Siphoninus phillyreae (Halliday, 1835)
Aleurodes phylliceae Bouché, 1851
Aleyrodes dubia Heeger, 1859
Aleyrodes phillyreae Haliday, 1835
Asterochiton dubius (Heeger, 1859)
Asterochiton phillyreae (Haliday, 1835)
Siphoninus dubiosa Haupt, 1932
Siphoninus finitimus Silvestri, 1915
Siphoninus granati Priesner & Hosny, 1932
Siphoninus phillyreae inaequalis (Gautier, 1923)
Siphoninus phillyreae multitubulatus Goux, 1949
Trialeurodes dubius (Heeger, 1859)
Trialeurodes inaequalis Gautier, 1923
Trialeurodes phillyreae (Haliday, 1835)
Biostatus and distribution
Ash whitefly was first found in New Zealand in a Devonport garden during May 1995. The European species, is also found in Western Asia, and North Africa. It has been spread to North, Central and South America, and Australia. After reaching high numbers, biological control has substantially reduced it to a minor pest. It is mainly found on susceptible ash trees, Fraxinus sp. (Oleaceae) and Hawthorne, Crataegus monogyna (Rosaceae).
Conservation status: Widespread, but rarely a pest.
Life stages and annual cycle
Ash whitefly has the same life stages and life cycle as the greenhouse whitefly, Trialeurodes vaporariorum. The adult whitefly has white wax covered wings and its yellow body is covered by a layer of white wax. The adults are about 1 mm long and have a wing-span of about 3 mm. When the adults emerge, the yellow body colour can be seen and the wings are transparent, but soon the wings become covered with white wax. There are males and females in this species. The generally smaller males may be seen sitting alongside females before mating.
Adult females lay eggs on the underside of the leaf. The oval eggs are laid on their sides but may have a peg at one end that is inserted into the leaf. They are pale coloured. The first larva to hatch from the egg has three pairs of legs and is usually called a crawler. It walks away from the egg and settles at a suitable feeding site, usually above or close to a leaf vein with phloem ducts (tubes that transmit nutrients from the leaf to other parts of the plant). The crawler is oval. There are four larval stages called instars. The larvae grow by moulting, (i.e. changing skin). The old skin splits on the upper dorsal side and the next larval instar pulls itself out and settles in the same place to feed. The third larval instar has short tubular papillae on upper side of its body. The fourth larval instar has more and longer tubular papillae and develops white wax along its midline. The larva has dark pigment at each end of its body. When the fourth instar larva reaches full size, it pupates inside the larval skin, which is now called a puparium. When the adult is almost ready to emerge, dark eyespots can be seen through the walls of the puparium. A T-shaped split occurs in the skin of the puparium which splits the front part of the wax on top of the body. The adult pulls itself out. Its body and wings harden, and become covered in white wax.
Feeding and honeydew
Whitefly adults and larvae have sucking mouthparts. Long specially shaped rods called stylets are held in the sheath-like rostrum. When it wishes to feed, the whitefly moves the tip of the rostrum onto the surface of the plant leaf. The stylets are then gradually pushed into the plant and manoeuvred into the phloem (or nutrient transport vessels) of the plant. The whiteflies suck the plant’s sap, which is high in sugars and low in other nutrients. Whiteflies excrete the excess sugary liquid, which is called honeydew. In the larvae, the excess liquid is excreted into a structure called the vasiform orifice where it accumulates. When a droplet has formed, a tongue-like structure called the lingula flicks the droplet away from the larva. It can be flicked up to 2 cm away.
Honeydew makes the plant leaves sticky. Sometimes black sooty mould fungi grow on the sticky surfaces.
In New Zealand, Ash whitefly is the only species of whitefly found on Ash trees, Fraxinus sp. (Oleaceae) and Hawthorn trees, Crataegus monogyna (Rosaceae). It has been found on other plants, but is now uncommon and unlikely to be found on less favoured hosts.
Ash whitefly can be readily distinguished from other insects with scale-like stages, by the distinct appearance of the white adults, the white wax along the midline of the puparium and the long papillae on the dorsal surface that exude droplets.
No pathogens or parasitoids of Ash whitefly are known in New Zealand.
The Ash whitefly parasitoid probably arrived in New Zealand at the same time as its host, Ash whitefly. It has contributed to the substantial decline in Ash whitefly populations. A second species of tiny wasp has been found in an Ash whitefly colony, but it is not known if it parasitises Ash whitefly.
The two known predators in New Zealand are both beetles from Australia. The Citrus whitefly ladybird, Serangium maculigerum, has been found feeding on the juvenile stages of several species whitefly and other insects with scale-like juvenile stages such as psyllids (Hemiptera: Psylloidea). While the Citrus whitfly predator, Cybocephalus species 1 (Coleoptera: Cybocephalidae) has only been found feeding on whitefly.
|Scientific Name||Common Name||Classification||Enemy Type||Reliability Index||Biostatus|
|Encarsia inaron (Walker, 1839)||Ash whitefly parasitoid (Wasp)||Hymenoptera: Aphelinidae||parasitoid||10||adventive|
|Cybocephalus species 1||Citrus whitefly predator (Beetle)||Coleoptera: Cybocephalidae||predator||8||adventive|
|Serangium maculigerum Blackburn, 1892||Citrus whitefly ladybird (Beetle)||Coleoptera: Coccinellidae||predator||10||adventive|
In New Zealand Ash whitefly is now only found on the underside of leaves of a few trees, Hawthorn, Crataegus monogyna (Rosaceae) and favoured species of Ash, Fraxinus sp. (Oleaceae). In the few years after it was first found in New Zealand, it was found on several other tree species. Records of those early discoveries are currently unavailable.
Feeding and honeydew
Adult and juvenile whiteflies feed by inserting their stylets into the phloem, the nutrient transport vessels of the plant. The whiteflies suck the plant sap and feeding by large numbers of them can debilitate the plant. Plant sap is high in sugars and low in other nutrients. Whiteflies excrete the excess sugary liquid, which is called honeydew. This makes the plant leaves sticky. Sometimes black 'sooty mould' fungi grow on the sticky surfaces.
|Common Name(s)||Scientific Name||Family||Reliability Index||Biostatus|
|Hawthorn, Neapolitan medlar, White hawthorn||Crataegus monogyna Jacq.||Rosaceae||10||naturalised|
|Black maire, Maire, Maire raunui, Pau||Nestegis cunninghamii (Hook.f.) L.A.S.Johnson||Oleaceae||10||endemic|
|Pomegranate||Punica granatum L.||Lythraceae||9||cultivated|
Now that there are several effective natural enemies established in New Zealand, Ash whitefly on native New Zealand plants are unlikely to warrant control. Ash whitefly can sometimes reach high numbers on the underside of leaves of Hawthorn and favoured species of Ash, Fraxinus sp. (Oleaceae). It is likely to be difficult to control by using insecticides alone. If insecticides are to be used, choose ones that causes least harm to the natural enemies. However, if Ash whitefly is causing problems, the best solution is to grow another tree.
Charles J; Froud K, 1996. Watch out for this new pest - Ash whitefly - Siphoninus phillyreae (Haliday) (Homoptera: Aleyrodidae). Orchardist, 69(9):41-43.
Martin NA 1999. Whitefly: Biology, identification and life cycle. Crop & Food Research, Broadsheet No. 91: 1-8.
Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/
Landcare Research New Zealand Limited (Landcare Research) for permission to use photographs.
The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.