The Content Of The Article:
- Life cycle and development
- Affected plants
- Symptoms and damage
- Preventive measures
- Combat the white fly
The white fly (Trialeurodes vaporariorum) is - despite the name - not a fly, because the insects are so-called moth sign lice. The animals are descended from an insect family closely related to the aphids and aphids.
The two to three millimeters large insects got their German name due to the whitish, covered with wax dust five millimeter wings. These are at rest roof-shaped on the abdomen and dominate the appearance of moth sign lice. The whitish wax is excreted in a gland that is also located on the abdomen. The hind legs of the white fly have a strong jumping muscles.
Life cycle and development
In their short life the females can deposit up to 400 eggs on the underside of the affected plants - that is about four to seven eggs per day! The eggs are 0.1 millimeters long and yellowish green. Under favorable environmental conditions, an entire generation can develop completely within just a few weeks. The development depends above all on the temperature: the animals need about two months to develop at about 16 degrees Celsius. At 24 degrees Celsius, however, a new generation is trained in less than half the time.
The female whitefly lays its larvae on the undersides of the plants
As oviposition time varies, the different stages of the whitefly - eggs, larvae and large insects - appear side by side. The larvae (nymphs) are whitish to transparent colored and unable to move. They suck on the underside of leaves the sap of the affected plants. In the fourth larval stage, white flies pupate in an oval pupal envelope - the so-called puparium. The adult animals then hatch out of the top.
The original range of white fly was probably the tropical and subtropical America - probably Brazil or Mexico. The small insects were finally introduced to Europe around 1848. The animals tolerate temperatures around the freezing point only for a short period of time. In Central Europe, therefore, they are only able to survive for a long time under favorable living conditions - such as those prevailing in the greenhouse, in the home and in warm outside temperatures.
The insects are not fussy and can eat from many different plants - from over eighty different families. Therefore, the animals are also referred to as polyphagous.
The white fly infects among other vegetables such as beans, cucumbers, tomatoes, cabbage, but also a number of ornamental plants. Particularly affected are annuals and balcony flowers and some trees - for example, rhododendron. In some cases, weeds are also affected. When touching the infected plant, the small insects fly numerous.
Especially in the greenhouse and in warm places in the garden it comes quickly to an extreme mass increase.
Symptoms and damage
Among other things, the plants are damaged by the suckling activities of the adult animals and their tiny larvae. But especially by separating the sticky honeydew the plants are weakened. At high temperatures and high humidity then the risk of fungal infection increases - the Rußtaupilz likes to settle under these conditions.
The leaves of the affected plants start to become stained and yellow when attacked by the white fly. In case of heavy infestation they dry up and consequently fall off.
To prevent an attack with the white fly, you can promote natural enemies such as spiders and parasitic wasps. A garden close to nature as well as the avoidance of broad effective pesticides make it possible to spread beneficial insects. Through a suitable living space, for example, parasitic wasps can also be kept in your garden for a long time. To do this, drill small holes in a log and place it in a suitable place in the countryside - soon, with a bit of luck, the helpful hymenoptera will settle here in large numbers.
The parasitic wasp is a natural opponent of the white fly and can protect against infestation
In addition, ventilate your greenhouse, the apartment and plants under foil regularly. Also, avoid excessive nitrogen fertilization.
Combat the white fly
As soon as you notice a whitefly infestation, you should act as quickly as possible to avoid mass proliferation.
So-called yellow boards or yellow stickers are suitable for controlling in the greenhouse. The tablets and stickers attract the pests with a special attractant.As a result, the pests remain attached to the panels and stickers and eventually wither away.
In the greenhouse, you can hang yellow sheets as traps
In the case of heavy infestations of indoor plants, balcony plants and in the greenhouse, the use of beneficial agents such as pest-free Naturen is recommended. The preparation based on rapeseed oil has an egg-killing effect. Also products of the neem tree are suitable for controlling the white fly. However, you should be careful to treat the undersides of the leaves sufficiently, because the white fly is mainly there. Bring the preparations thoroughly to the affected plants several times a week.
The parasitic wasp Encarsia formosa is also an important biological pest controller. The beneficial insects parasitize the larvae of the white fly and lay their eggs in them. As a result, the parasitic stages turn black. After some time, new parasitic wasps hatch from the discolored pupal sheaths, creating a helpful population of beneficial insects. Incidentally, which of the two animals hatched from the egg, can be easily understood at the opening of the smear. If the exit hole is round, a parasitic wasp hatched, while the white fly leaves a T-shaped opening.
The parasitic wasp acts on the white fly in two different ways: on the one hand, young developmental stages are pierced and sucked out - this deadly process is also called "host-feeding" -, on the other hand, the older stages of development are effectively parasitized.
The use of commercially available parasitic wasps is particularly suitable in enclosed areas such as in the greenhouse or conservatory. The parasitic wasps are usually glued and shipped on cardboard cards in the resting doll stage. For a successful fight average temperatures of at least 17 degrees Celsius are required. Such beneficials are particularly helpful at the beginning of an infestation.