The aleurodids – more commonly called whiteflies – are insects belonging to the Aleyrodoidea family, which – in turn – are part of the homoptera, a very large species with over 1500 living subspecies. These white insects can destroy tender or leathery plants, and transmit diseases.
They are not easy to manage, and different methods can be used to eradicate them over the course of a few weeks.
This white plant parasite has its origins in tropical countries, but – due to its nature, its great capacity to adapt to various environments and to resist even different temperatures compared to those of the places where it originates – it has managed over time to spread evenly throughout the world.
Certainly, given its origins, it is easier to find the white fly in warm, poorly ventilated and humid places, such as greenhouses, where it causes the greatest inconvenience.
The most widespread aleurodids in Italy – which nest mainly on the stems and between the leaves of our plants – are the Trialeurodes Vaporiorum, better known as greenhouse aleurodids, precisely because they prefer to spread and shelter in damp and sheltered places, such as the small plastic tunnels that are installed in vegetable gardens, but also in real traditional greenhouses. Precisely for this reason it is commonly called aleurodide of greenhouses.
The white fly: the origins and diffusion
Originally from Central America, the whitefly has gradually spread to the temperate and warm regions of our country (in particular, it is much more present in southern Italy and much less so in northern regions). In the northern and central areas of our peninsula, in fact, it almost exclusively frequents greenhouses and – more generally – sheltered and covered cultivations; however – in some particular conditions – it is also possible to find them in open fields.
For this reason and – as we have seen – for its great ability to adapt to the surrounding environment, the plants that risk being infested by the aleurodide are many.
Whiteflies are insects that live in colonies and nest in the lower part of the plants, or on the lower part of the leaves. Once settled, they begin to feed on the sap obtained by sucking the ribs with their particular mouthparts.
What does the whitefly look like: what do the aleurodids look like?
The whitefly looks a lot like the butterfly, which is why they are often identified also with the name of white plant butterflies or – more simply – white butterflies, because they are even pleasing in appearance. These parasites, in fact, could look like real moths, but in reality they are relatives of the aphids, much more feared and dangerous.
White flies have a body about 1.5-2 millimetres long, very soft and completely covered by a sort of waxy powder, which gives them protection and the typical creamy white color.
The larvae of these parasites are small caterpillars and nest in the lower part of the leaves, nourishing – as we have seen – of their sap. Most species of insects belonging to the whitefly family reproduce best when the ambient temperature is 27-33°C.
How do the aleurodids reproduce?
The aleurodids reproduce rapidly and – precisely for this reason – it is particularly difficult to eradicate them; this rapidity, in fact, allows a massive proliferation: generations of insects reproduce consistently throughout the year.
The adults, usually, are found on the upper part of the leaf of the plant, flying as soon as the plant moves. The female specimens, on the contrary, lay their eggs in the lower part of the leaf and each female is able to lay about 100/150 eggs (in some cases it can even reach 200). About 12 days after the laying, the neanids will be born, which – after having passed three neanidal stages and one nymphal state – are ready at the major age. At this point these insects are to all intents and purposes whitefly capable of attacking plants and all this happens within about a month.
Whiteflies reproduce sexually, but for some particular species there can also be parthenogenesis.
Some species of these white insects regenerate only once a year (this is the case for example of the species attacking the olive tree), but – as a general rule – they can have 2 to 4 cycles each year. However, if the conditions of the environment are particularly favorable, the numbers can be much higher. Greenhouses, for example, are a perfect environment both to welcome them and to accelerate their reproduction.
White flies: where do they nest and what damage do they cause?
White flies – as mentioned above – are common pests found in gardens, both indoor and outdoor. Usually they hide behind the lower part of the leaves and feed on their sap there, causing yellowing and weakening the plant; in cases where the plant is attacked massively, it begins to progressively defoliate and weaken until it dies.
The aleurodids – as we have seen – are insects that genetically feed by sucking and – in this way – can also spread viruses and bacteria, producing a lot of honeydew and allowing the development of soot. These white plant pests are generally visible to the naked eye – although they are small in size – but if you have doubts and want to be sure, you can shake the plant. Once the branches and leaves are moved, you can see a mass of tiny white flies taking flight. In this way, you will have the certainty of their presence.
Which plants affect the aleurodide?
The aleurodidae – or whiteflies – are parasites that feed on many varieties of plants, in particular they attack begonia, dahlia, surfinia, fuchsia, cyclamen, but they can also easily be found on many other types of plants, both garden and orchard, even on very young trees.
The whiteflies affect in particular – as we have seen above – all the plants cultivated in the greenhouses, but there are, however, some of them which are affected, in a particular way, more than others. Among these we find tomatoes (perhaps you might also be interested in the guide to growing tomatoes) grown very often in greenhouses, but also aubergines, watermelons and also many ornamental plants, among which – in a particular way – it is worth mentioning poinsettias.
But there is more, because there is a specific family of aleurodids that attacks citrus fruits in a particular way and – for this reason – identified with the name “citrus white fly”.
During the winter period, the aleurodehyde frequently nests among the leaves of vegetables, particularly in the leaves of cabbage, where they feel more sheltered, and then move away with the arrival of mild and cold temperatures.
However, it is good to specify – for completeness and precision – that these white parasites, identified with the name “white fly” or “greenhouse fly”, in reality, do not represent one only species; there are, in fact, several sub-families of this insect which can infest with the same modalities and create very similar damages. For convenience, we identify them all with the more generic term of whitefly or aleurodidae.
In this regard, we point out that another very common insect of the aleurodide is the “aleurodida tabacii” or tobacco aleurodide.
The whitefly on citrus fruits: all you need to know
As mentioned above, a particular type of whitefly often nests also on citrus plants, always in the lower part of the leaves and with the same methods of attack implemented on other plants. In particular, if the aleurodehyde attacks a lemon tree (here you can find the complete guide for growing lemons indoors or outdoors) or any other citrus fruit, which is not particularly strong and robust, the consequences for the plant are harmful and irreversible: at first the leaves turn yellow, then they start to fall and this leads to the slow but definitive death of the shrub.
Problems created by the whitefly
The damage caused by the whitefly, unfortunately, is comparable to that of aphids, with the difference that – in this case – the fight is much more complicated, also because it seems that they quickly become resistant to the various active ingredients.
The damage caused by these insects are:
- The stings: the whiteflies suck the sap from the plants, as a result of which there will be sap removal and reactions from the plant, necrosis and leaf drying. There will be loss of vitality, colour and productivity.
- Honeydew: Plants release adhesive honeydew and this can contribute to the formation of mould on the plants. In addition, this is an obstacle to chlorophyll photosynthesis, which is accompanied by the development of cryptogams and product damage. The leaves appear stained, reclined and lose vigor.
- Transmission of virosis: whiteflies are virus vectors, particularly on the tomato plant, where this weed is a frequent problem.
White Fly: How to prevent it and natural remedies to defend your plants
Various strategies can also be implemented to prevent and combat whitefly.
- Buy plants only from serious and professional dealers, who you trust, who make a preventive fight.
- Protect the plants during the transition from the nursery to the greenhouse/cultivation area by means of special fine-meshed nets, able to avoid the passage of even the smallest insects.
- Also the place where you grow must be well protected and isolated from the outside, with special screens.
- Very important is the periodic monitoring of weeds, especially in areas close to the plants you want to protect.
- Provide yellow chromotropic traps and place them about 10 cm away from the plants, so that whiteflies can remain trapped.
Furthermore, it is recommended to keep the temperature of the indoor garden or greenhouse below 27°C, in order to hinder the reproduction of the whitefly, which – as we have seen – fears the cold. It is also necessary to clean the plants with lemongrass vegetable soap. The use of a dust filter in the inlet air duct can prevent whitefly from entering.
What to do when the aleurodids have already arrived? All the main remedies
But what can you do when the white fly has already arrived in our garden or orchard?
Whiteflies are an important problem and a danger not to be underestimated, especially because they reproduce quickly, becoming numerous in a short time over an entire crop. However – and this is the good news – they are not impossible to eliminate. The important thing, however, is to act now so that the damage can be contained.
First of all, it should be remembered that the aleurodid – being equipped with wings just like butterflies – flies from one leaf to another and from one plant to another, so trying to remove these insects manually or detach part of the plant – for example, as is common for rose aphids – is hardly ever a sufficient method. It is effective for removing larvae, but it does not help to fight the already formed and winged insect.
In any case, as a first attempt, it is always worthwhile to implement these systems.
Secondly, yellow chromotropic traps can be used to catch and stop adult whitefly to fight the aleurodids. These are strips of glue coloured yellow, which first attract these annoying insects and then imprison them (in essence, they work just like the strips to kill the flies we usually use during the summer). The yellow chromotropic traps should be hung about 20 centimetres above the plant to be protected and – as seen above among the preventive systems – it is advisable to place them in the growing space or in the greenhouse before placing your plants.
Another way to prevent and hinder the proliferation of whiteflies in cultivation is to create an inhospitable environment for these pests who hate cold and love high and humid temperatures: ventilate the greenhouse (or growing environment) frequently, allowing cold air to enter and spread.
Another effective – and always natural – way to fight these white plant gnats is to spread natural enemies in the protected growing environment, thus triggering a biological fight.
Among the natural enemies of whiteflies we find the curvy encarsia, which lays its eggs right among the whitefly’s enemies, immediately triggering a biological battle.
But the biological fight against the aleurodid can also be carried out using the chalcidoid hymenoptera, or the Encarsia tricolor, insects that manage to contain – quite effectively – the aleurodidae, especially if they do not use insecticides that slow down their development.
But that’s not all, because – in specialized shops – you can also find bacteria that infest both eggs and adults of aleurodide: these are Beauveria bassiana and Verticillium lecanii.
Finally, another remedy always effective to protect the garden from external attacks is represented by ladybugs, which are antagonists not only of aleurodids, but also of many other dangerous parasites.
Defending against whiteflies is a very difficult battle to fight. In fact, these parasites lay their eggs very quickly and this leads to continuous aggression against the plant. In addition, another characteristic of aleurodidae is their ability to resist normal, commonly sold pesticides and this is due to the layer of wax that covers the eggs and protects them from enemies, including insecticides.
The white butterflies, in fact, are particularly strong and resistant, so much so that they adapt quite easily to the various active ingredients of the products used; for this reason it is advisable to vary – from time to time – the type of product and the active ingredient, to prevent these parasites from getting used to them.
How to eliminate aleurodides: organic remedies and traditional/chemical insecticides against white gnats
Beating the whitefly with an organic and natural product is not so easy, also because – nesting in the lower part of the leaves – they often manage to escape treatment.
Among the natural remedies recommended to fight them is definitely neem oil and pyrethrum, which are able to kill the aleurodide. Alternatively, it is advisable to use garlic or hot pepper macerate, which have a repellent effect against the parasite.
However, the action of chemical insecticides is the one that offers the best results at the moment: it is recommended to carry out close treatments with ad hoc remedies, one every seven days for a period of about 30 days.
The most recommended products are those that include pyrethrum.