Whitefly, Greenhouse Whitefly

Trialeurodes vaporariorum

Services Related Content
Changed on: 08.10.2018
Icon Icon Icon
Eine adulte weiße Fliege (Trialeurodes vaporariuorum)
caption
Adulte Weiße Fliege

The greenhouse whitefly (Trialeurodes vaporariorum) is a member of the whiteflies (Aleurodidae), a subgroup of the Sternorrhyncha group.

They were imported from East Africa about 100 years ago and are now found on many crops cultivated in our greenhouses. Their German name comes from the fact that their larvae are glued to the leaves in a similar way to a scale insect, while the adult insects are unable to fly, like tiny white moths.  

Eine adulte weiße Fliege (Trialeurodes vaporariuorum)
caption
Adulte Weiße Fliege

The greenhouse whitefly (Trialeurodes vaporariorum) is a member of the whiteflies (Aleurodidae), a subgroup of the Sternorrhyncha group.

They were imported from East Africa about 100 years ago and are now found on many crops cultivated in our greenhouses. Their German name comes from the fact that their larvae are glued to the leaves in a similar way to a scale insect, while the adult insects are unable to fly, like tiny white moths.  

Symptoms

Symptoms

Infested plants do not suffer a great deal of damage from the insect’s direct feeding, but from larvae excretion containing sugar. Whiteflies excrete a sticky honeydew, in a similar way to aphids. Given that these organisms prefer to sit on the underside of the leaf, the honeydew drips onto the leaves and fruits below. This shiny coat is a good habitat for sooty moulds. These moulds soil the fruits (additional rinsing necessary) and the affected leaves lose their assimilation surface, weakening the plant.

Host Plants

An extraordinary number of ornamental plants and even weeds are affected, in addition to cucumbers, tomatoes and aubergines, but also bell peppers and beans on rarer occasions. Whiteflies are limited to greenhouses – maybe even the close such surroundings in more moderate climate zones, as they do not survive the winter outdoors. This does not apply to tropical climates, of course.

 

 

Diagnosis

caption
Whitefly eggs
Weiße Fliege oder Gewächshausmottenschildlaus (Trialeurodes vaporariorum) - Eistadium
caption
Whitefly larvae instar
Weiße Fliege oder Gewächshausmottenschildlaus (Trialeurodes vaporariorum) im Larvenstadium
caption
Whitefly in its last instar
Weiße Fliege oder Gewächshausmottenschildlaus (Trialeurodes vaporariorum) im letzten Entwicklungsstadium
caption
Whitefly skin remains (exuvie)
Häutungsreste (Exuvie) der Weißen Fliege oder Gewächshausmottenschildlaus (Trialeurodes vaporariorum)

The adult insects are about 2 mm in size and have two pairs of wings and are covered with fine, white wax powder. Their eyes are separated into upper and lower halves by tissue.
Usually, they sit well protected on the undersides leaves and jump off using their hindlegs when disturbed, going into flight. The 0.25 mm long, ellipsoid eggs are anchored to the underside of young leaves with a little stem, which also supplies them with moisture.

Freshly laid eggs are white, but turn increasingly darker during their six to eight day development period (at 20 °C).

Development Phases

During the first instar, the larvae look for a spot to tap into the plant’s sap for feeding on their birth leaf and will not leave that spot.

The insects are fixed to the leaf from their second instar onwards. They insert their stylets into the phloem (in a similar way to aphids) and feed on the sugary sap taken from their hosts vascular bundles. Egg-laying females are often found on the higher, younger leaves on host plants with several levels of leaves, such as cucumbers or tomatoes; the larvae are found on the leaves on the middle section and the hatching whiteflies on the lower, older leaves.
Eggs, larvae and adult animals require fresh plants to survive and die after short periods of time when stuck on wilted leaves. Their development comprises four instars, similar to scale insects, in which they grow up to 0.8 mm. In their first instar, they can still move and have functioning extremities, which they will lose later.

All their instars are mainly translucent, showing only a few yellow spots inside their bodies. These spots are inhabited with symbiotic bacteria, which produce important vitamins for the whiteflies.

These bacteria migrate from the mother insect into the unfinished eggs during the egg development stage, thus, being transferred to the organisms of the next generation.
The last instar (pseudopuparium) looks like a tiny, minute, oval cylinder with vertical walls and is white-to-yellow in colour. The development period from the egg to the finished adult insect takes about 25 to 30 days. As a result, it is possible that several, overlapping generations develop every year. 

The whitefly can only survive the winter on green plants in glasshouses or homes, as it has no hibernation form and is very susceptible to cold temperatures.

Control

Preventing them from overwintering: overwintering ornamental plants (hanging plants in hallways or neighbouring houses) present a particular risk. Fuschias, Gerbera and many other ornamental plants are often severely infested.
Preventing migration: never move from a heavily infested greenhouse to one that is not infested.

Monitoring: to notice initially harmless whitefly infestations in time, sticky yellow whitefly traps just should be put just over the tips of the plants. The yellow colour attracts various pests, including whiteflies, dark-winged fungus gnats and leaf miners. The insects are attracted and then get stuck on the glue. However, yellow whitefly traps alone are not enough to combat whiteflies effectively.

Chemical Control

Spray products for sap-sucking insects can be used to combat them chemically. A minimum of two treatments will be necessary at an interval of five to seven days to kill all instars in cases of mixed infestations with all development groups. The whitefly is prone to developing resistances to the substances used in insecticides, which forces frequent changes in active substance groups. Substances authorised for the use in Austria are listed in the plant protection product register (see BAES plant protection product register). 

Biological Control

Releasing Encarsia formosa, a species of chalcid wasps: this tiny chalcid wasp injects its eggs into the young whitefly larvae, causing a wasp to emerge from the now black pseudopupae as a result of the infection of the larvae with the parasite. Information on quantities, release intervals and possible combinations with other plant protection products should be provided by the producer of the beneficial insects. Small quantities of chalcid wasps are often released prophylactically on young plants, in particular, perennial plants. Furthermore, it should be noted that parasitic infections with chalcid wasps are less effective in autumn and winter than during spring and summer. The additional use of selective, beneficial insect-friendly plant protection products might be required in individual cases. 

Substances such as potash soap and pymetrozine can be combined well with the use of chalcid wasps. All pyrethroids, such as deltamethrin and cypermethrin are not recommended for use with beneficial insects. There are no waiting periods for the use of oil and soap products.
The lower leaves should not be removed too quickly when using beneficial insects because this would also remove Encarsiae that have not yet hatched!

Other useful, beneficial insects include Eretmocerus mundi, a parasitoid wasp from the Ichneumonide family, and the predatorial true bug, Macrolophus caliginosus, which works well in combination with Encarsia.

 

 

x