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Pests

Whiteflies (Aleurodoidae ssp.)

Traleurodes vaporariorum

Greenhouse whiteflies (Trialeurodes vaporariorum).
The population will soon rise if the climate conditions are optimal.
Photo :Magnus Gammelgaard.

Traleurodes vaporariorum

Greenhouse white flies (Trialeurodes vaporariorum) imago laying their eggs at the backside of a tobacco leaf.
Photo :Magnus Gammelgaard.

Traleurodes vaporariorum

Adults (Trialeurodes vaporariorum). At right pupae wich will soon be hatching. Left you can see empty pupae.
Photo :Magnus Gammelgaard.


Traleurodes vaporariorum

Pupae of Greenhouse Whiteflies (Trialeurodes vaporariorum) are higher than those from cotton whiteflies.
Foto :Magnus Gammelgaard.


Traleurodes vaporariorum

Greenhouse whiteflie hatching from pupae (Trialeurodes vaporariorum) .
Photo :Magnus Gammelgaard.


White flies………..No they are not flies but people like to mention them like that.
If you look at the picture above it is difficult to imagine that this nice looking fly, is considered to be a serious pest.
The size is about 1 mm and the fact that the adults and nymphs normally are to be found at the backside of the leaves, causes that it is the symptoms, which first are to be seen.

Traleurodes vaporariorum

Eggs of the greenhouse whiteflies (T. vap.), placed at the backside of a tobacco leaf.
A: These new eggs, not older than 1-2 days, are pale. B: Older eggs are darker.
Photo :Magnus Gammelgaard.


Symptoms
The first symptoms are some shiny, sticky stuff at the leaf surface. These sugary substances called honeydew are the remains from the whiteflies ore to be more correct, the nymphal stages. After some time the covered areas are turning brownish ore dark because they are overgrown by black sooty mould.
The leaves get an anaesthetic look at the whole plant looks dirty. If you carefully look at the backside of the leaves, you will be able to find adults, nymphs, pupae and eggs.
The sooty mould cowering the leaves, also are inhibiting the photosynthesis. The growth are also inhibited by the sucking of the whiteflies.




Trialeurodes vaporariorum

Greenhouse whiteflies (T.vap). Stages of nymphs at the backside of a leaf.
A: eggs, B: newly hatched nymphs (crawlers), C: nymphs in the 3-4 nymph stage ("pupae"), D: an empty pupae (the whitefly has left it).
Photo :Magnus Gammelgaard.


Species
Forskellige arter er almindelige i Danmark.
  • Greenhouse Whiteflies (Trialeurodes vaporariorum)
  • Cotton Whiteflies (Bemisia tabaci)
  • Rhododendron Whiteflies (Dialeurodes chittendeni)
  • Strawberry Whiteflies (Aleyrodes lonicerae )
Normally in Denmark, it is indoor in winter gardens, conservatories ore greenhouses that white flies gives the most trouble.
The greenhouse whiteflies are the ones, which is most common to be found. They can have several generations per year, depending of the temperature. The imagoes are laying upright standing eggs, placed in nice circles if the backside of the leaf is smooth. That is because the whitefly rotates in circles using the mouthparts in the plant as a centre. If the backsides of the leaves are not smooth, the eggs are scattered around.

After 3-4 days the colour of the eggs changes from pale white to black. The total time from egg laying to hatching is 7-1 days at 20 degrees centigrade.
Newly hatched nymphs (called crawlers) are during the first day, moving around to find a good place to feed. Then they are placing the mouthparts deeply in the plant tissue. After that they are losing their legs and are not able to move any more for the rest of the lifecycle.
After 3 chances of skin, the pupae stage ends, and the nymphs are developed to the adult whitefly. The whole lifecycle takes about 1 month at a mean temperature at 20 degrees castigates. The imago has a sort of built in reflex, which makes them fly at the direction at the top of the plant.
There for you will normally find eggs and adults at the top leaves of the plant and the nymphs at the lower leaves.



Cotton whiteflies (Bemisia tabaci) at
the backside of a leaf.
Photo :Magnus Gammelgaard.

Bemisia tabaci

Cloze up of cotton whitefly
(Bemisia tabaci) on a poinsettia leaf.
Photo :Magnus Gammelgaard.



Bemisia tabaci

Cotton whitefly; a= eggs, b=newly hatched mymph, c=nymph in the second instar. (Bemisia tabaci)Here on poinsettia
Photo :Magnus Gammelgaard.



Bemisia tabaci

Cotton whitefly; a=nymph which nearly has reached teh "pupal stage", b=Empty pupae "case". Picture from Poinsettia(Bemisia tabaci)
Photo :Magnus Gammelgaard.



Bemisia tabaci

Cotton whitefly "pupae" (notice the 2 reed eyespots).The colour varies depending of the host. Picture from Poinsettia. (Bemisia tabaci)
Photo :Magnus Gammelgaard.



Bemisia tabaci

Here the adult cotton whitefly is leaving the pupae. (Bemisia tabaci)
Photo :Magnus Gammelgaard.



Bemisia tabaci

Honeysuckle Whitefly, adults on the bagsite of the leaves. (Aleyrodes lonicerae)
Photo :Magnus Gammelgaard.



Bemisia tabaci

Honeysuckle Whitefly. (Aleyrodes lonicerae)
Photo :Magnus Gammelgaard.



Bemisia tabaci

Honeysuckle Whitefly, nymphs, parasitided nymphs, hatched pupae. (Aleyrodes lonicerae)
Photo :Magnus Gammelgaard.


Host's
A large number of our plants for indoor growing can be attacked from greenhouse whiteflies.
In hobby greenhouses it is especially tomatoes, sweet pepper, aubergine are very susceptible when talking about wedge tables. In ornamentals Fuchsia, Pelargonium, Begonia can be mentioned, but the numbers of host are enormous only the leaves are not to bee to thick, so that the whiteflies are able to penetrate the leaf tissue.

The cotton whitefly is often to be mixed up with the greenhouse whitefly, but it needs a higher temperature. In Denmark we try to avoid the cotton whitefly, but sometimes it is imported together with plants, especially poinsettia cuttings.
Denmark was until 2001 considered being a restricted zone for Bemisia and findings lead to strong precautions from the authorities.
The fear were based on the fact, that this whitefly were able to transfer some dangerous virus diseases and also because this species is more difficult to control with ordinary pesticides. Denmark is no longer a restricted zone for Bemisia, but findings leads to export restrictions.

Control

Aktiv stof Handelsnavn Mere information
Snyltehvepse
Mellus-rovtæge
Mellus-mariehøns
Swirskii-rovmide
Verticillium lecanii
Kaliumoleat
Thiacloprid
Imidacloprid
Imidacloprid
pyrethrin I og II +piperonylbutoxid
cypermethrin
Flere
Macrolophus caliginosus
Delphastus pusillus
Amblyseius swirskii
2)Mycotal
Insektsæber-flere
Calypso
Provado Spray
Provado Insektpind
1)Spruzit Insektfri Total
Maladan insektmiddel
Nyttedyr.dk  Bioproduktion 
Bioplant  Bioproduktion
Bipolant  Bioproduktion
Bipolant
Bipolant  Bioproduktion
Egne sider
bayergarden.dk
  "
  "
ECOstyle A/S
bayergarden.dk

1) The product contains natural pyrethrum and a synergist that reinforce the effect.

2) The product is a microbial agent, which contains beneficial fungi.

For controlling this pest a lot of control possibilities both biological and chemical are to be found.
As the pest is a problem in professional nurseries both in ornamentals and in wedge tables, new natural enemies to be used, are to be found all the time.
In this matter it is necessary to look at every new beneficial and its demands for the surrounding environment, to be able to get a good control.




Adult parasitoid (encarsia formosa) which have developed from a whitefly numph.


If one chooses to spray it is important also to cover the backsides of the leaves, especially if you are using a pesticide that only works with contact.
The active ingredient imidacloprid is however systemic and can be transported around the plant in the xylem. This has been confirmed when using the Provado insect stick, which is to be placed in the soil where the active ingredient is dissolved and taken up by the plant.
The plant has to be active growing; otherwise the insecticide will not work.


Precautions
Check out the plants before receiving them and take in to quarantine at optimal climate. Wash down the backsides of the leaves with cold water can kill some adults. If they are left to dry however, they are able to fly again and return to the plant. Remove the leaves: If it is possible to recognize the leaves with nymphs and pupae, those can be removed.

Low temperatures: At temperatures below 15 degrees centigrade, the development goes very slow

Alternative control  look at
botaniskpest.htm

Opdateret d. 6.1.2014
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