INTERESTING INSECTS

By N A Martin (2017)

Eucalyptus whitefly

Aleuroclava eucalypti Dumbleton, 1957

This adventive whitefly comes from Australia. It was first discovered on a host plant, Tasmanian bluegum, Eucalyptus globulus Labill. (Myrtaceae), in Blenheim, New Zealand in 1950 by Mr. Dumbleton. It has since been found on Mainland Australia.

Conservation status: Widespread, a minor pest on Tasmanian bluegum and other species of Eucalyptus.

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]

In Auckland, it appears to overwinter as larvae and pupae. It breeds all through spring, summer and autumn. There are several generations per year, the number depending on temperature. Its generation time is shorter in summer when it is warmer.

Eucalyptus whitefly has the same life stages and life cycle as the greenhouse whitefly, Trialeurodes vaporariorum. The adult whitefly is covered with white wax. The adults are about 1.8 mm long and have a wing-span of about 3 mm. When the adults emerge, the yellow body colour can be seen with black markings on the thorax (middle section of the body) and the wings are transparent, but soon the body and wings become covered with white wax. There are males and females in this species. Males may be seen sitting alongside females before mating.

Adult females lay eggs on the surface of the leaf in partial circles around where they are feeding. 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 at first, darken to pale tan over the next few days. Eggs are laid on young and old leaves. 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, flat and transparent with yellow body contents showing. There are four larval stages. The larvae grow by moulting, (i.e. changing skin). The old skin splits on the upper (dorsal) side and the next larval stage pulls itself out and settles in the same place to feed. When the fourth stage (or 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, black eyespots can be seen through the walls of the puparium. A T-shaped split occurs in the skin of the puparium and 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 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.

Adult and puparium of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2G7S]

Eggs of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae), laid in rings on a young leaf, not the white wax deposited on the leaf. Creator: Tim Holmes. © Plant & Food Research. [Image: 2G7Y]

Eggs of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae), laid in rings on a young leaf, not the white wax deposited on the leaf. Creator: Tim Holmes. © Plant & Food Research. [Image: 2G7Z]

Eggs of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae), laid in rings on an old leaf with old puparial cases. Creator: Tim Holmes. © Plant & Food Research. [Image: 2G80]

Eggs of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae), laid in on an old leaf. Creator: Tim Holmes. © Plant & Food Research. [Image: 2G82]

Eggs and first instar (stage) larvae of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2G81]

Eggs and first three larval instars (stages) of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2G83]

Puparia of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae), note the eye spots of two about to emerge, one in the process of emergence and one empty with split dorsal skin. Creator: Tim Holmes. © Plant & Food Research. [Image: 2G7V]

Puparium of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae), note the eye spots. Creator: Nicholas A. Martin. © Landcare Research. [Image: 2G84]

Puparia of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae), with two adults in the process of emerging, one empty with split dorsal skin and one with eyespots. Creator: Tim Holmes. © Plant & Food Research. [Image: 2G7W]

Adult and puparia of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2G7T]

Eucalyptus whitefly is the only species of whitefly known on Eucalyptus species in New Zealand.

Adults and puparia of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2G7R]

Eggs and white wax from adults of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae), on host plant leaf. Creator: Tim Holmes. © Plant & Food Research. [Image: 2G7X]

Eggs and first three larval instars (stages) of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2G83]

An unidentified species of Encarsia (Hymenoptera: Aphelinidae) has been reared from puparia of this whitefly.

No other parasitoids, predators or fungal pathogens of the Eucalyptus whitefly have been recorded in New Zealand. Birds, spiders and predatory insects are likely to feed on them.

Eucalyptus whitefly, Dumbletoniella eucalypti is known from several other Eucalyptus sp. (Myrtaceae), including the Tasmanian bluegum, Eucalyptus globulus, on which it was discovered in Blenheim.

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.

Adults and puparia of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2G7R]

Eggs and white wax from adults of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae), on host plant leaf. Creator: Tim Holmes. © Plant & Food Research. [Image: 2G7X]

Eggs and first three larval instars (stages) of Eucalyptus whitefly, Dumbletoniella eucalypti (Hemiptera: Aleyrodidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2G83]

Eucalyptus whitefly can reach moderate numbers on some young trees, but despite the absence of any specific natural enemies, it does not appear to cause significant harm to plants.

Dumbleton LJ. 1957. The New Zealand Aleyrodidae (Hemiptera: Homoptera). Pacific Science. 11: 141-160.

The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.

Landcare Research New Zealand Limited (Landcare Research) for permission to use photographs.

1 December 2018. NA Martin. Changed symbol used for apostrophes.