INTERESTING INSECTS

By N A Martin (2018)

Ash whitefly

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)

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.

Diagramme of the life cycle of the greenhouse whitefly, Trialeurodes vaporariorum (Hemiptera: Aleyrodidae). Creator: Based on figure 20 from Crop & Food Research Broadsheet 91. © Plant & Food Research. [Image: 3BG]

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.

A recently emerged adult female and puparia of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of a Hawthorn tree, Crataegus monogyna (Rosaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDN]

Adult female and puparia of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of a Hawthorn tree, Crataegus monogyna (Rosaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDL]

Eggs and young larvae of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of an Ash tree, Fraxinus sp. (Oleaceae): note the white wax left by the adults wings. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDD]

Eggs and young larvae of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of a Hawthorn tree, Crataegus monogyna (Rosaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDP]

Eggs and the four larval instars (stages) of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of an Ash tree, Fraxinus sp. (Oleaceae): note the white wax down the midline of the fourth instar larvae (right) and the black pigment at the front and back. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDF]

Third instar (stage) larva of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae): note the short wax fringe and the tubular papillae on the body. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2TD0]

Microscope slide preparation of a third instar (stage) larva of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae): note the tubular papillae on the body. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2TD2]

Fourth instar (stage) larva of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae): note the white wax fringe down the and the long tubular papillae with droplets. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2TD1]

Microscope slide preparation of a fourth instar (stage) larva of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae): note the long tubular papillae on the body and the dark pigment at each end. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2TD3]

Larvae of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of a Hawthorn tree, Crataegus monogyna (Rosaceae): note the white wax down the midline of the fourth instar (stage) larvae that also have black pigment at both ends, and the presence of liquid at the tips of tall papillae on larvae. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDU]

Fourth instar (stage) larvae and puparia of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of a Hawthorn tree, Crataegus monogyna (Rosaceae): note the tubular papillae with droplets on their bodies. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDV]

Adult female and several empty puparia of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of an Ash tree, Fraxinus sp. (Oleaceae): note that an adult is in the process of emerging from its puparium. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDC]

Adults and puparia of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of a Hawthorn tree, Crataegus monogyna (Rosaceae): note the black eyespots in the emmerging adult. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDM]

Adult female emerging from its puparium and a fully formed femela Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of an Ash tree, Fraxinus sp. (Oleaceae): note the unexpanded wings of the emmerging adult . Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDG]

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.

Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of an Ash tree, Fraxinus sp. (Oleaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2TD7]

Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of an Ash tree, Fraxinus sp. (Oleaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2TDA]

Adult females and puparia of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of an Ash tree, Fraxinus sp. (Oleaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2TD6]

Larvae of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of a Hawthorn tree, Crataegus monogyna (Rosaceae): note the white wax down the midline of the fourth instar (stage) larvae that also have black pigment at both ends, and the presence of liquid at the tips of tall papillae on larvae. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDU]

Eggs and young larvae of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of an Ash tree, Fraxinus sp. (Oleaceae): note the white wax left by the adults wings. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDE]

No pathogens or parasitoids of Ash whitefly are known in New Zealand.

Parasitoids

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.

Predators

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.

Wasp (Hymenoptera) parasitoid round exit holes puparia of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae): note that one puparium (upper right) is black indication the presence of a parasitoid pupa. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDT]

Two images of the upper side of the Ash whitefly parasitoid, Encarsia inaron (Hymenoptera: Aphelinidae) parasitoid of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDS]

Two images of the underside of the Ash whitefly parasitoid, Encarsia inaron (Hymenoptera: Aphelinidae) parasitoid of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDR]

Adult male Citrus whitefly predator, Cybocephalus species 1 (Coleoptera: Cybocephalidae): note the large pronotum, the first segment behind the head. Creator: Tim Holmes. © Plant & Food Research. [Image: 2MMN]

Larva of Citrus whitefly predator, Cybocephalus species 1 (Coleoptera: Cybocephalidae) on a leaf of hawthorn with ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MN3]

Larva of Citrus whitefly predator, Cybocephalus species 1 (Coleoptera: Cybocephalidae) on a leaf of ash, Fraxinus sp. with ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MN9]

Larva of Citrus whitefly predator, Cybocephalus species 1 (Coleoptera: Cybocephalidae) making a cocoon on a leaf of hawthorn with ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MN5]

White cocoon of Citrus whitefly predator, Cybocephalus species 1 (Coleoptera: Cybocephalidae) on a leaf of ash, Fraxinus sp. with ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2MNB]

Adult citrus whitefly ladybird, Serangium maculigerum (Coleoptera: Coccinellidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 163X]

Larva of citrus whitefly ladybird, Serangium maculigerum (Coleoptera: Coccinellidae). Creator: Minna Personen. © Plant & Food Research. [Image: 164L]

Large larva of citrus whitefly ladybird, Serangium maculigerum (Coleoptera: Coccinellidae), on citrus leaf. Creator: Tim Holmes. © Plant & Food Research. [Image: 164F]

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.

Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of a Maire, Nestegis cunninghamii (Oleaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TD4]

Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of a Maire, Nestegis cunninghamii (Oleaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TD5]

Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of an Ash tree, Fraxinus sp. (Oleaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2TD7]

Upper side of a leaf of an Ash tree, Fraxinus sp. (Oleaceae) with dark sooty moulds in the honeydew from Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) living on the underside leaves. Creator: Tim Holmes. © Plant & Food Research. [Image: 2TD8]

Upper side of a leaf of an Ash tree, Fraxinus sp. (Oleaceae) with dark sooty moulds in the honeydew from Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) living on the underside leaves. Creator: Tim Holmes. © Plant & Food Research. [Image: 2TD9]

Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of an Ash tree, Fraxinus sp. (Oleaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2TDA]

Colony of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of an Ash tree, Fraxinus sp. (Oleaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDB]

Larvae of Ash whitefly, Siphoninus phillyreae (Hemiptera: Aleyrodidae) on the underside of a leaf of a Hawthorn tree, Crataegus monogyna (Rosaceae): note the white wax down the midline of the fourth instar (stage) larvae that also have black pigment at both ends, and the presence of liquid at the tips of tall papillae on larvae. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2TDU]

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.