INTERESTING INSECTS

By N A Martin (2010, revised 2015)

Cabbage whitefly, European cabbage whitefly

Phalaena (Tinea) proletella Linnaeus, 1758

Aleyrodes proletella (Linnaeus) Latreille, 1801

Coccus prenanthis Schrank, 1801

Aleyrodes prenanthis (Schrank) Cockerell, 1902

Aleyrodes brassicae Walker, 1852

Aleurodes euphorbiae Löw, 1867

This adventive whitefly comes from the northern hemisphere. It is naturally present in parts of Europe, Asia and Africa, and has spread to North and South America, Australia and New Zealand. It is widespread in New Zealand and is a minor pest of cabbages and related plants, and some flowers. It is also found on two native plants, New Zealand celery, Apium prostratum Labill. ex Vent. (Umbelliferae) and New Zealand sea spurge Euphorbia glauca G.Forst. (Euphorbiaceae), and weeds.

Conservation status: Widespread, a minor pest of some vegetable crops, flowers and two native plant.

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 places with cold winters, cabbage whiteflies overwinter as adults. In Auckland, it appears to breed all year round. There are several generations per year depending on temperature. Its generation time is shorter in summer when it is warmer.

Cabbage whitefly has the same life stages and life cycle as the greenhouse whitefly, Trialeurodes vaporariorum. The adult whitefly is covered with white wax and each forewing has two black marks. The adults are about 1.5 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 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 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, darkening over the next few days, and have a yellow spot inside. 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, red 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 honey dew

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 honey-dew. 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. Honey-dew makes the plant leaves sticky. Sometimes black sooty mould fungi grow on the sticky surfaces.

Newly emerged adult cabbage whitefly, Aleyrodes proletella (Hemiptera: Aleyrodidae); note the yellow body colour and transparent wings before they are covered with white wax. Creator: DSIR photographers. © Plant & Food Research. [Image: 3BD]

Adult cabbage whitefly, Aleyrodes proletella (Hemiptera: Aleyrodidae); note the black mark on the white wings. Creator: DSIR photographers. © Plant & Food Research. [Image: 3B6]

Eggs of cabbage whitefly, Aleyrodes proletella (Hemiptera: Aleyrodidae); Newly laid eggs are cream coloured and darken after a few days. Creator: DSIR photographers. © Plant & Food Research. [Image: 3B7]

Juvenile stages of cabbage whitefly, Aleyrodes proletella (Hemiptera: Aleyrodidae); eggs, egg shells and four larval stages. Creator: DSIR photographers. © Plant & Food Research. [Image: 3BC]

Scanning electron micrograph of a fully grown of cabbage whitefly, Aleyrodes proletella (Hemiptera: Aleyrodidae); on the right-hand side, the vasiform orifice that contains the tongue-like lingula, the structure used to flick away droplets of excess sap and sugar. White scale bar = 1 mm. Creator: Paul Sutherland. © Plant & Food Research. [Image: 3B8]

Adult cabbage whitefly is the only species of whitefly in New Zealand with black marks on its wings. The moth fly, Psychoda alternata Say, 1824 (Diptera: Psychodidae), may be confused with cabbage whitefly. It also has white wings with black patches, but is larger. Moth flies have larvae that feed on decaying plants and do not damage live plants.

Juvenile cabbage whiteflies are the only whiteflies found breeding on New Zealand sea spurge, (Euphorbia glauca (Euphorbiaceae)). It is also the whitefly most likely to be found on cabbages and related plants, and on puha (Sonchus species (Compositae)).

Adult cabbage whitefly, Aleyrodes proletella (Hemiptera: Aleyrodidae); note the black mark on the white wings. Creator: DSIR photographers. © Plant & Food Research. [Image: 3B6]

An adult moth fly, Psychoda sp. (Diptera: Psychodidae). It is larger than an adult cabbage whitefly and has a fuzzier outline. Creator: DSIR photographers. © Plant & Food Research. [Image: 3BB]

No predators or fungal pathogens of the cabbage whitefly have been recorded the in New Zealand, though some species of lacewings and ladybirds are known to feed on whitefly. It is also likely that spiders and other generalist insect predators feed on whiteflies.

Parasitoids

Encarsia formosa Gahan, 1924 (Hymenoptera: Aphelinidae), the black and yellow whitefly parasitoid released in New Zealand in 1936 for control of greenhouse whitefly, also parasitises cabbage whitefly. A brown parasitoid, Encarsia pergandiella Howard, 1907 (Hymenoptera: Aphelinidae), from North America was discovered in New Zealand in the 1970s. It is common in New Zealand on greenhouse whitefly, and also attacks cabbage whitefly. In Europe a yellow whitefly parasitoid, Eretmocerus eremicus (Rose & Zolnerowich 1997) (Hymenoptera: Aphelinidae), has been reported parasitising cabbage whitefly. This parasitoid was recently discovered in New Zealand.

Two adult female whitefly parasitoids, Encarsia formosa Gahan, 1924 (Hymenoptera: Aphelinidae); this species is used to control greenhouse whitefly. Creator: DSIR photographers. © Plant & Food Research. [Image: 3BA]

Adult female whitefly parasitoid, Encarsia perganiella Howard, 1907 (Hymenoptera: Aphelinidae), upper side. Creator: Tim Holmes. © Plant & Food Research. [Image: 15AB]

Adult female whitefly parasitoid, Encarsia perganiella Howard, 1907 (Hymenoptera: Aphelinidae), underside. Creator: Tim Holmes. © Plant & Food Research. [Image: 15AC]

Adult female whitefly parasitoid, Encarsia perganiella Howard, 1907 (Hymenoptera: Aphelinidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 15AD]

Cabbage whitefly, Aleyrodes proletella (Hemiptera: Aleyrodidae), puparia parasitized by Encarsia perganiella Howard, 1907 (Hymenoptera: Aphelinidae); note the parasitoid exit hole and the dark pigment of parasitoids in other puparia. Creator: Tim Holmes. © Plant & Food Research. [Image: 15AE]

Cabbage whitefly, Aleyrodes proletella (Hemiptera: Aleyrodidae), puparia parasitized by Encarsia perganiella Howard, 1907 (Hymenoptera: Aphelinidae); note the parasitoid exit holes and the dark pigment of parasitoids in other puparia. Creator: Tim Holmes. © Plant & Food Research. [Image: 15AF]

Cabbage whitefly, Aleyrodes proletella (Hemiptera: Aleyrodidae), puparia parasitized by Encarsia perganiella Howard, 1907 (Hymenoptera: Aphelinidae); note the parasitoid exit holes and the dark pigment of parasitoids in other pupari. Creator: Tim Holmes. © Plant & Food Research. [Image: 15AG]

In New Zealand, cabbage whitefly has been found breeding on one native New Zealand plant, the sea spurge Euphorbia glauca (Euphorbiaceae). It also lives on crop plants (brassicas), garden flowers (a blue and white species of Aquilegia (Ranunculaceae)) and 'weeds' such as sow thistle, Sonchus oleraceus, also known as puha. In other countries, the cabbage whitefly breeds on other plants in the daisy family (Compositae) and on plants in other families such as broad beans (Leguminosae) and poppies (Papaveraceae).

Adult whitefly will lay eggs on some plants of black nightshade, Solanum nigrum (Solanaceae), but all the young first stage (instar) larvae die, so the plant is not one on which the insect can breed. The reliability index for this plant species is 2.

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 honey-dew. This makes the plant leaves sticky. Sometimes black 'sooty mould' fungi grow on the sticky surfaces.

Adult and juvenile cabbage whitefly, Aleyrodes proletella (Hemiptera: Aleyrodidae) on the underside of a cabbage leaf. Creator: DSIR photographers. © Plant & Food Research. [Image: 3BE]

Larvae and puparia of cabbage whitefly, Aleyrodes proletella (Hemiptera: Aleyrodidae) on the underside of leaf of New Zealand Cellery, Apium prostratum (Umbelliferae). Creator: Tim Holmes. © Plant & Food Research. [Image: 1KBB]

Cabbage whiteflies on native New Zealand plants are unlikely to warrant control. Cabbage whiteflies can sometimes reach high numbers on vegetable brassicas. It is often difficult to control whitefly by using insecticides alone.

Non-insecticide controls include: Removing weed host plants and other less important plants that are hosts of cabbage whitefly; this reduces the inoculum and source of adults to infest the crop plants,

Having a break in the year from growing the plants on which cabbage whitefly multiplies well,

Removing leaves with large numbers of juvenile whitefly and burying or composting the leaves so that adults do not emerge,

Spraying the underside of leaves with soapy water will kill adult whiteflies.

Insecticides

Most insecticides will kill only adult or very young larvae of the cabbage whitefly. Eggs, older larvae and puparia are resistant to most insecticides. This means that a single application of most insecticides will not give adequate control of whitefly. Usually a sequence of applications is required to kill emerging adults before they lay many eggs, and to kill the young larvae when they hatch from eggs and before they grow and moult into larger larvae.

If insecticide sprays are used, they should be directed onto the undersides of leaves. In addition, chemicals that cause least harm to natural enemies should be selected.

More information about controlling whitefly can be found at resistance.nzpps.org/index.php?p=insecticides/whitefly.

Use in biological control

Although the cabbage whitefly breeds on plants from many families, it does not breed on cucurbits. Scientists in the Netherlands have used this information to demonstrate how cabbage whitefly can be used to improve biological control of greenhouse whitefly on greenhouse cucumbers. They established some plants of nipplewort (Lapsana communis L. (Compositae)) and greater celandine (Chelidonium majus L. (Papaveraceae)) in the cucumber greenhouse and colonised these plants with cabbage whiteflies. The whitefly parasitoid, Encarsia formosa Gahan, 1924 (Hymenoptera: Aphelinidae), was released into the greenhouse to attack the greenhouse whitefly on the cucumbers. Some also established a breeding colony using the cabbage whiteflies as hosts. Adult parasitoids that hatched from the cabbage whitefly could spread to the cucumber plants and attack the greenhouse whitefly. The nipplewort and greater celandine plants with cabbage whitefly are called 'banker plants'. They provide a reservoir of a natural enemy that can help to control a pest in a crop by providing a continuously breeding source of the beneficial organism.

Australian Biological Resources Study (ABRS) (accessed January 2010). www.environment.gov.au/biodiversity/abrs/online-resources/fauna/afd/taxa/Aleyrodes%20proletella .

Finch S, Thompson AR 1992. Pests of Cruciferous Crops. In: McKinlay RG ed. Vegetable Crop Pests. London, UK, The Macmillan Press. Pp. 87-138.

Martin NA 1999. Whitefly: Biology, identification and life cycle. Crop & Food Research, Broadsheet No. 91: 1-8.

Martin NA 2005. Whitefly insecticide resistance management strategy, updated February 2005. resistance.nzpps.org/index.php?p=insecticides/whitefly.

Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/.

van der Linden A, van der Staaij M 2001. Banker plants facilitate biological control of whiteflies in cucumber. Proceedings of Experimental Applied Entomology 12: 75-79.

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

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

6 February 2015. NA Martin. Recognition: added photo of adults. Natural enemies: added photographs of Encarsia pergandiella. Host plant list updated