Whitefly Infestation: Effective Strategies for Organic Defense

The whitefly is an insect of the order Hemiptera, family Aleyrodidae. It is a very problematic parasite for horticulturists who have chosen to operate in a biological regime. This is especially true because it has a very rapid and prolific development cycle, making it difficult to control. This insect causes various types of damage to plants and can also act as a vector for some serious viruses. In today’s article, we will talk about biological defense strategies to eliminate it from our crops.

But first, let’s get to know the different species present in our territory and see how to identify them.

The different species of whiteflies

The whitefly is native to tropical and subtropical zones in Asia, but it has adapted very well to our climate, especially in southern regions. There are several species present in our territory, and the most significant ones are three:

The Trialeurodes vaporariorum, or greenhouse whitefly
The Bemisia tabaci, or garden whitefly
The Dialeurodes citri, or citrus whitefly.

In terms of visual identification, the species are very similar and can be differentiated only by small details that are difficult to observe. Due to this and also considering their similarities in the biological cycle, we have decided to discuss them together. The most marked differences are related to the specific damage caused by each species, but by following our suggestions, you should be able to avoid them.

Most affected plants

The different species of whiteflies cause damage in a more or less specialized manner to vegetable, tree, and ornamental crops. Let’s take a closer look at the plants affected by these three varieties.

Trialeurodes vaporariorum

This species, also known as the greenhouse whitefly, as the name suggests, prefers greenhouse vegetable crops. It particularly attacks Solanaceae (tomato, eggplant, pepper), Cucurbitaceae (zucchini, cucumber) and Cruciferae (cauliflower, savoy cabbage, black broccoli).

Bemisia tabaci

The common name for this species is garden whitefly. It attacks the same crops as Trialeurodes vaporariorum, but it is more prevalent in open fields.

Dialeurodes citri

Dialeurodes citri, also known as citrus whitefly, affects not only citrus fruits like lemon or orange, but also other fruit trees such as persimmon, pomegranate, and kiwi. Additionally, it can attack other ornamental plants or shrubs such as privet, gardenia, etc.

Identification and biological cycle

The common name “whitefly” is related to the appearance of adult specimens. These adults, depending on the species, have a length ranging from 1 to 3 mm and are yellowish in color, with typical white wings resembling those of a fly.
The entire body is covered with a layer of waxy and dusty microparticles, which serve as natural defense for the fly while also soiling the vegetation of the affected plants.
Other characteristics of the insect include a globular-shaped head with slightly pronounced vertex and purple-colored eyes. It also has a piercing-sucking mouthpart through which it feeds on plants.

Young stages

Even the young stages of the whitefly are problematic. In this phase, the fly is much smaller, has little mobility, and stays on the undersides of the leaves for a long time, where it produces abundant honeydew.
Whiteflies, in general, reproduce by oviposition, laying very small elongated eggs that are fixed on the underside of leaves.

Generations

Whiteflies can have a variable number of generations in a year. For example, in greenhouse crops, they have a continuous cycle that lasts about 30 days and continues during the winter months, then moving outdoors in the summer months. In open fields, they overwinter on spontaneous plants and then resume their activity in spring.
In general, under favorable climatic conditions, these insects can go through four or more generations, causing several problems.

Damages caused by whiteflies

Whitefly honeydew

The damages caused by whiteflies to crops are of different types. Firstly, there is the damage to the leaf vegetation caused by their trophic activity (feeding punctures) in different stages of their development. Nutritional punctures reduce the lymphatic circulation of plants and consequently hinder their growth.
Another serious damage of whiteflies is the abundant production of honeydew, similar to what happens with scale insects. This has several repercussions:

It dirties the fruit;
The honeydew layer reduces the photosynthetic activity of plants and causes leaf asphyxiation;
The honeydew intensifies the effect of sunlight, causing burns on the plants;
Furthermore, it leads to the development of sooty mold, creating additional aesthetic and photosynthetic problems.

Another serious problem caused by whiteflies is the spread of viruses, which are specific and severe plant diseases. For example, the species Bemisia tabaci is responsible for the Tomato Yellow Leaf-Curl Virus (TYLCV), while Trialeurodes vaporariorum transmits the Tomato Infectious Chlorosis Virus (TICV).

Eliminating whiteflies

Whitefly attack on a tomato leaf

First of all, let’s say that biological defense against whiteflies is complex due to several factors. Firstly, this is an insect with high reproductive potential, capable of multiple generations in a year, especially in greenhouse crops. Then, there is the issue of high mobility of adult specimens, which tend to cluster under the leaves and fly away quickly at the slightest movement. Additionally, commercial crop selection and extensive pesticide use have reduced biodiversity in our environments, affecting the natural defense action of predatory insects.
That being said, let’s see how we can defend our crops against this insect using biological remedies.

Natural predators

Among the natural predators used primarily for whitefly control in greenhouses or under tunnels is the parasitic wasp Encarsia formosa (family Aphelinidae). This micro-wasp, of North American origin, is bred in bio-factories and is successfully used, especially against the species Trialeurodes vaporariorum.
The female parasitizes the young stages of whiteflies, laying an egg inside them; the parasitized whitefly, in turn, will parasitize other young whitefly forms.
The natural predator is commercially available in the form of cards, kept at low temperatures, with young whitefly forms already parasitized by the wasp attached to them.
Since this insect is not well acclimated to our temperatures, it does not survive our winter, even in a greenhouse. Therefore, continuous re-population releases are necessary.
Another natural predator is the predatory bug Macrolophus caliginosus.

Chromotropic traps

Another biological remedy to eliminate whiteflies, effective both in greenhouses and open fields, is the use of yellow chromotropic traps.
Since whiteflies are particularly attracted to the color yellow, placing numerous traps can achieve effective mass capture. You can find an excellent product of this kind at this link.

Marseille soap

Another biological remedy against whiteflies is the use of Marseille soap. It is best to apply it in the early hours of the day. When the whitefly comes into contact with the soap solution, it dies of asphyxiation due to the soap’s drying effect on its body. Marseille soap is also useful for washing plants from honeydew. The difficulty in using this solution lies in the high mobility of the insect, which tends to hide under the leaves and fly away when it detects water spraying. Therefore, some care is required during application.
If you want to purchase Marseille soap formulated specifically for agriculture, you can find it at this link.

Sulfur powder

Finally, another effective biological remedy against whiteflies is sulfur powder. In this case, the action is repellent, as the whitefly cannot stand the presence of sulfur and tends to move away. Therefore, if applied preventively, infestation can be avoided.
The limitation of this defensive strategy lies in the whitefly’s rapid reproductive rate and the succession of new generations. Sulfur powder, as already mentioned when discussing powdery mildew, must be used with caution and not too frequently to avoid leaf burning. It is essential to act before large infestations occur.
To apply sulfur powder, you need to use a sulfur duster such as this one, and you can find sulfur powder at this link.

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