Whiteflies are threatening your tomatoes!

The whitefly is a small insect belonging to the Hemiptera order, characterized by its body being entirely covered with a white, waxy layer. Females are typically larger and have a lifespan ranging between 28 to 30 days, during which they can lay approximately 150 eggs.

There are two primary types of whiteflies: Bemisa tabaci and Trialeurodes vaporaririum. While both can be harmful to crops, infestations with B. tabaci are considered more significant as they act as vectors for plant-pathogenic viruses. However, infections caused by T. vaporaririum are a common issue in greenhouses and high-altitude areas.

Viruses transmitted by whiteflies can severely reduce crop yields and, in extreme cases, lead to the complete destruction of crops, particularly when infections occur during the early stages of plant development. Farmers may suffer losses of up to 100% of their yield.

In 1988, the Tomato yellow leaf curl virus (TYLCV), belonging to the Begomovirus and Geminiviridae types, emerged in the Mediterranean region. Initially, this virus caused substantial losses due to limited knowledge of its transmission mechanism and prevention methods. Subsequent research revealed that whiteflies are responsible for transmitting this virus, which is considered one of the most devastating viral diseases associated with them, posing a significant threat to greenhouse cultivation.

The presence of whiteflies can also pose a serious threat as pests, particularly during late summer. The outbreak of viral diseases, such as TYLCV, practically brought field tomato cultivation to a halt along the Mediterranean coast for over two decades.

It is important to note that controlling whiteflies is challenging and complex due to their rapid development of resistance to chemical pesticides.

Whiteflies are characterized by their soft-bodied, delicate nature, with wings covered in a white, powder-like waxy layer. Their bodies are typically light yellow, while immature stages appear yellowish-white, often found on the undersurface of leaves.

The secretions from whiteflies can stimulate the growth of sooty mold, which can impede plant growth, especially if the infection occurs during the early stages of the plant’s life cycle. Additionally, whitefly infestations can leave marks on fruits, underscoring the importance of prevention until the crops’ fruiting stage has ended.

Common signs of whitefly presence include pale and wilted leaves, as these insects feed by sucking sap from the undersides of leaves.

When approaching treated plants to inspect the underside of wilted leaves, one may notice the presence of dozens or hundreds of small white insects hovering in the form of a cloud. In severe infestations, other insects, such as aphids (as secondary pests), may accompany the disease.

Additionally, as a result of the infection, sticky substances and honeydew secreted by the whitefly become apparent.

The whitefly located on the underside of the leaves

Aphid infestation combined with whiteflies

The appearance of the sooty mold fungus which grows on honeydew

Tomato plant infected with the Tomato yellow leaf curl virus TYLCV
which is transmitted by the whitefly

The whitefly reproduces both sexually and asexually. Female insects are produced from eggs, while males are produced asexually. Females lay up to 150 eggs during their lifespan, attaching them to the underside of leaf surfaces, typically favoring smaller, younger leaves. These eggs hatch within eight to ten days.

Upon hatching, the eggs give rise to mobile nymphs with legs and antennae, sporting 12 pairs of nymphs on their sides. Initially, these nymphs crawl briefly before settling to feed on plant tissue.

The nymphs progress through four stages, each lasting approximately four days. In the second and third nymphal stages, the nymphs become stationary, remaining attached to the leaf to continue feeding. They continue to feed until reaching the fourth and final nymphal stage, often referred to as the pupa or red-eyed nymph. At this stage, they cease feeding to emerge as adult insects.

Adult whiteflies are highly active and play a key role in spreading plant pathogenic viruses among healthy plants. The life cycle of the whitefly, from egg to nymph to adult, typically spans 10 to 28 days in warm weather. In colder temperatures, such as during winter, the generation time lengthens to 30 to 48 days. Under favorable conditions, the whitefly can undergo 15 to 18 generations per season.

Main Stages of Damage| During the second and third nymphal stages, the whitefly nymphs feed on leaves and sap, while adult whiteflies continue to feed and transmit plant pathogenic viruses.

Whiteflies are multi-host pests, capable of infesting crops in both open fields and protected environments. Their feeding activity primarily targets the undersides of leaves, where they absorb large quantities of plant juice, leading to severe weakening of the plant.

Initially, yellow spots of varying sizes and areas develop on the leaves due to this feeding activity. In severe cases, only the veins of the leaves remain green, while the rest of the leaf may appear brown and dry. Plant wilting and leaf shedding may occur, with advanced infections often accompanied by the presence of black, sticky mold on the leaves and stems of affected plants.

Other symptoms of whitefly infestation include stunted growth and wrinkled leaves. New leaves may emerge small and wrinkled, with yellowing observed between the veins. The edges of the leaves may become twisted and cup-shaped.

Infected plants often exhibit a discolored appearance, particularly noticeable in the short internodes. Flowers may fail to set, flourish, or drop prematurely.

Significantly, fruit production declines, especially if the infection occurs early in the plant’s life cycle.

Severe infestations of whiteflies can have devastating consequences for plants, particularly tomatoes, as whiteflies are significant vectors of plant pathogenic viruses. The virus is acquired by the whitefly through feeding on infected plant tissues (bark tissues), requiring at least 15 minutes of feeding before acquisition. Subsequently, the whitefly must feed for 15 to 30 minutes to transmit the virus to a healthy plant or other hosts.

Nutrition and the absorption of plant sap are critical aspects of the whitefly’s lifecycle and contribute to the spread of plant diseases.

1. Crop Monitoring: Surveillance for whiteflies should commence at an early stage of plant growth. An effective method is to gently brush or shake the leaves while observing for flying adults. Additionally, remnants of the skins of the small whiteflies may be visible on the undersides of leaves.
2. Use of Hand Lens: A hand lens can aid in examining both stages of the whitefly (adult and young). Adults and young whiteflies can be distinguished by the shape of their wings, which take on a somewhat vertical, slightly slanted shape. Another characteristic is the positioning of the wings, resembling a ceiling where they do not meet above the surface but leave a small space separating them. Neighboring plants in the field can also be inspected for the presence of whiteflies.
3. Yellow Sticky Traps: Yellow sticky traps are effective in predicting the presence of whitefly infestations. These traps can be strategically placed throughout the crop area to capture adult whiteflies, providing valuable information for monitoring and control efforts.

Tomato Spotted Wilt Virus (TSWV):

• Transmission method: Thrips (Frankliniella occidentalis).
• Symptoms: Color heterogeneous rings or gnawing on leaves and fruits.

Cucumber Mosaic Virus (CMV):

• Transmission method: Non-persistent insect vectors.
• Symptoms: Often stunted and distorted leaves. An overlap between dark green and lighter green tissues may be observed, resembling symptoms caused by other viruses. Thin, threadlike leaves are characteristic of CMV infection.

Tobacco Mosaic Virus (TMV):

• Transmission method: Through infected plant seeds and by touching infected plants.
• Persists in infected plant remains.
• Symptoms: Contrasting areas between light green and dark green on leaves. Leaves on infected plants are often small and wrinkled.

Tomato Yellow Leaf Curl Disease:

• Transmission method: Whitefly (Bemisia tabaci).
• Symptoms: Necrotic spots causing leaf yellowing, curling, and upward cupping, leading eventually to leaf drying.

Tomato Yellow Leaf Curl Virus (TYLCV) is a highly destructive pathogenic virus that severely impacts tomato production in numerous countries worldwide.

This virus is efficiently transmitted by adult whiteflies, with an acquisition period ranging from 5 to 20 minutes and an incubation period lasting from 8 to 24 hours.

Research has demonstrated that TYLCV can be transmitted through offspring resulting from eggs laid by infected insects. Remarkably, TYLCV DNA has been detected in the offspring of insects infected with the virus via eggs. These adult insects and their offspring are capable of infecting indicator plants and inducing typical disease symptoms.

Tomato Yellow Leaf Curl Virus – TYLCV

Tobacco Mosaic Virus – TMV

Cucumber Mosaic Virus – CMV

Managing whiteflies requires an integrated approach that combines various strategies to effectively control these pests. In tomatoes, sweet and hot peppers, farmers can implement several practices to mitigate whitefly infestations:

1. Follow proper agricultural methods, including arranging field practices such as periods free of host plants and agricultural cycles. Monitor fields routinely to identify infection hotspots and use pesticides only when necessary.
2. Grow crops under protected conditions, especially during the seedling stage until the beginning of flowering. Select and develop varieties that are tolerant or resistant to viral infections.
3. Maintain healthy, strong plants through proper soil selection, spacing, watering, weed control, and fertilization practices. Avoid excessive nitrogen fertilizer, as it can exacerbate damage to delicate plant tissues.
4. Implement biological control methods by preserving natural enemies of whiteflies, such as parasitic wasps and predatory bugs, found on wild plants near fields. Utilize yellow sticky traps to monitor and trap adult whiteflies.

5. Employ agricultural practices and physical methods that deter whiteflies, such as avoiding wearing yellow clothing, using yellow traps in fields and greenhouses, and collecting and disposing of infected leaves.

6. Use insect nets and reflective mulches to cover greenhouses and deter whiteflies. Plant barrier crops like corn along field borders to prevent whiteflies from entering.

7. Incorporate chemical control methods judiciously, as whiteflies have developed resistance to many pesticides. Rotate pesticide groups and apply them according to the critical economic level of whitefly infestation.

8. Consider using vegetable oils to suffocate whiteflies and insecticides with vapor effects to target adult whiteflies. Debbane Agri offers various solutions for whitefly control, including sticky yellow strips, modern insecticides like Sivanto Prime, and biopesticides such as Siltac.

By adopting an integrated approach to whitefly management, farmers can effectively mitigate the impact of these pests on their crops and ensure sustainable agricultural practices.

by Eng. Taher Abu Fakher