Gardening

Aleurodide, whitefly


GeneralitŠ°


This parasite is native to tropical countries, thanks to its great resistance, and its ability to adapt, it has spread throughout the globe in a fairly uniform way.
It is present above all in hot and humid places, for this reason it is mainly present in greenhouses, where it also causes the greatest damage, the development of whiteflies it is also favored by poor ventilation. The parasite feeds on many varieties of plants, be they coriaceous or tender, among these the most common are: begonia, dahlia, surfinia, cyclamen, fuchsias, petunias, marigolds, poinsettias and almost all varieties of geranium. The whiteflies most common on our ornamental plants are Trialeurodes vaporiorum, or greenhouse aleurodide, and Bemisia tabacii, or tobacco aleurodide.
They are usually nestled on the underside of the leaf, where they feed on causing leaves to turn yellow and weaken the plant, in the event of severe attacks the plant can defoliate and die.
The aleurodidi are insects with a sucking lambente apparatus, for this reason they can also propagate viruses and bacteria.
These pests produce a lot of honeydew that fills the leaves and on which fumaggini can develop.

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These insects have a rapid reproductive cycle, which allows several generations during the year. The adults are usually on the underside of the leaf, their presence is easily seen as they fly each time the plant moves. The females lay their eggs on the underside of the leaf, each female lays on average between 150 and 200 eggs, after a period of 10-12 days the nymphs are born, these must pass through three neanidal stages and a nymphal state in order to become adults, this operation usually takes a month.

Defense




The fight against the aleurodidi is very hard, this for the frequency of the depositions, that provokes the presence of more stages of development in the same period of time, for their high resistance to the most common pesticides on the market, and also for the waxy film which cover the eggs, protecting them from the pain of insecticides.
Adults can be caught with chromotropic traps (they are made of pieces of plastic colored yellow and sprinkled with glue), which will be hung about twenty centimeters above the plant.
The chemical fight is the one that at the moment gives the best results, it is appropriate to perform fairly close treatments, one every week for a month, using products based on pyrethrum, headache, dimethoate + endosulfan, or with imidacloprid, repeating the treatment once per month.
Biological control can be carried out in protected environments, using the calcidideous hymen Encarsia formosa and Encarsia tricolor, these natural antagonists are able to contain enough glia aleurodidi, especially if insecticides are not used which slow down their development. Bacteria can also be found on the market that parasitize the eggs and the aleurodide adults, these are Beauveria bassiana and Verticillium lecanii.

Description and origins


The alaleodide of the greenhouses is an insect belonging to the family of the aleyrodidae, commonly called "white fly". It measures about two millimeters and is cream white in color, similar to a small butterfly, and represents one of the most known and feared plants parasites.
This species is native to Central America and has spread accidentally in temperate or warm regions (such as southern Italy). In the northern and central areas of our peninsula it frequents greenhouses almost exclusively. The parasitized plants are very many: tomatoes, aubergines, watermelons, but also many ornamental ones among which in particular the Christmas stars. In any case, it can also be present in the open field, especially in areas where winters are mild.

Habits



They live in colonies that are located in the lower part of the plants and in any case on the underside of the leaves. Once they have established themselves in a certain environment they begin to feed on the sap obtained by pricking the ribs through their sucking mouthparts.
They produce eggs and generally they reproduce by sexually even if in some species there may also be parthenogenesis.
Some make only one generation a year (for example for the typical species of the olive tree), but in general they can have from 2 to 4. In favorable environmental conditions it is possible to arrive at much higher numbers making the fight very difficult.
For example, inside the greenhouses it can happen that a complete cycle lasts even just three weeks. For these types there are many generations from spring to autumn inside and then, during the winter, there is the transfer outside on annual herbaceous plants.

Which plants can we find them on?


These pests feed on a fairly small number of plants, but if necessary they are able to adapt and expand their range of action. However, angiosperms are exclusively affected. The plants for which they are more harmful are the solanaceae, the legumes, the curcubitacee, the tobacco, the citrus fruits and also many ornamental plants.

For this type of approach, contact insecticides such as pyrethroids can be used. Systemic or trans laminar products can also be useful.It is also possible to distribute agrochemicals based on white oil, perhaps mixed with an insecticide.A very effective method in greenhouses for prevention is the annual use of fumigation (in particular with products such as methomyl, sulfostep or sulfur), before starting the crop cycle.Integrated fight


In this case the struggle through antagonistic individuals can be really useful. The introduction of parasitoids such as the Encarsia formosa can be considered (although in the southern regions it is not particularly effective and can be used only from spring to autumn.
Encarsia lahorensis and clithosteus arcuatus, especially citrus fruits, are quite effective.

Aleurodide, whitefly: Other methods



Various strategies can also be implemented for prevention and control.
- Protect the seedlings during transport by nets or non-woven fabric.
The greenhouse must also be isolated from the outside by applying special nets to windows and entrances.
- It is of paramount importance to control weeds near crops.
- Buy seedlings only from nurseries that do prevention.
- Apply yellow chromotropic traps, one every 5 m2, above the vegetative apex of the plant, about 10 cm away, before putting them into the greenhouses.