- What are Whiteflies?
- Whiteflies are hemipterous insects belonging to the Aleyrodidae family. They can cause considerable damage and loss of production.
- What can you see?
- Discolored patches on the parts of the leaf where the insects have been feeding.
- What can you do?
- One of the main objectives when controlling whitefly is to prevent the crop being infected by a virus that the insects can be carrying.
Whitefly are Hemiptera insects belonging to the Aleyrodidae family. They are considered a major pest for plumeria because they cause considerable damage. They feed by sucking the sap from the host plant. They are polyphagus, meaning that they feed on many different plants, and so they represent a hazard for the majority of crops, as well as feeding off wild plants and weeds that act as a reservoir for the pest.The characteristic white color of these insects is due to a layer of white powder that covers both their bodies and their two pairs of wings.The two species of whitefly that affect plumeria are Bemisia tabaci or tobacco whitefly and Trialeurodes vaporariorum or glasshouse whitefly. The main morphological difference that enables these insects to be distinguished from one another is the position of the wings. In B. tabaci, they are joined to the body and in T. vaporariorum they are parallel to the surface of the leaf. Furthermore, the adult and pupa of T. vaporariorum usually has a greater quantity of waxy powder than B. tabaci.
Biological cycle of Whitefly
The full life cycle of the whitefly lasts between 15 and 40 days, depending on environmental conditions, particularly the temperature, since eggs will develop into adults more quickly when the temperature is higher. The whitefly usually lays its eggs on the underside of the leaves, which the eggs stick to.
The whitefly usually lays its eggs on the underside of the leaves and the eggs stick to them by means of a pedicel. The larva or nymphs emerge from the eggs and in their first stage of development, they are mobile enough to move along the leaf until they find the right place to insert their stylus and begin to feed off the sap of the phloem, which is rich in sugars. The nymphs then pass through several more stages of development, during which they remain in the same place and continue to feed off the plant until the adult emerges from the last nymph stage. Non-fertilized eggs produce males while the fertilized eggs produce females.
Symptoms and Damage of the whitefly
The direct damage is caused to the plant when the whitefly feeds. The sucking of the sap causes discolored patches on the parts of the leaf where they have been feeding. Furthermore, as they suck out the sap, they release toxic substances into the phloem, which then spreads throughout the plant. This leads to metabolic imbalances in the plant and general weakening, chlorosis and changes to the flowers and fruit. In terms of indirect damage, the molasses excreted by the nymphs enables fungi, such as sooty mold (Capnodium sp.), to form on the leaves. This mold acts as a screen and reduces the photosynthetic capacity of the plant.
However, the most serious damage that the whitefly can cause to crops is the transmission of viruses. These include the TYLCV (Tomato yellow leaf curl virus), the ToCV (Tomato chlorosis crinivirus) or the TYMV (Tomato Yellow Mosaic Virus).
How to prevent the pest?
One of the main objectives when controlling whitefly is to avoid the crop being infected by any virus that the insects may be carrying. It is therefore important that, any weeds or remains of other plants, near the crop are removed because these can act as a habitat for whitefly. Furthermore, if a whitefly feeds off a weed that has a virus and then reaches your crop, the virus can easily spread. The use of protective barriers such as nets and covers are also a good option for preventing infestations.
Biological Control
A range of entomophagus insects, parasites, and some entomopathogenic fungi are used to control whitefly.
Most of the predators used feed on the eggs and nymphs of the whitefly. This category includes the Delphastus catalinae beetle. The chrysopidae larva and some bedbugs are also good biological controllers of this pest.
The small wasps of the Aphelinae family are parasites of the whitefly larva, where the wasps lay their eggs and they develop by feeding off their host. They are the most commonly used parasite wasps and are specific to the pest that they live off. This results in a quicker control of the pest, even though their specific nature means that they are not useful against other phytophagous insects.
Entomopathogenic fungi can also be used. This infects and grows inside the whitefly and eventually kills it. New spores emerge out from the corpse and infect other individuals. One example is the Verticillium lecanii fungus.
Whitefly (Bemisia tabaci) just emerged from its final nymphal stage, the fourth-instar nymph (pupa). Surface of hibiscus leaf. High magnification (5x) image showing the soft waxy appearance of this insect. This whitefly has a size of less than 1mm.
Cultural control measures
One of the main objectives when controlling whitefly is to avoid the crop being infected by a virus that the insect can carry.
Therefore, any weeds or remains of other plants that are near the crop should be removed as these can act as a habitat for the whitefly. Furthermore, if a whitefly feeds off a weed that contains a virus and then reaches your crop, the virus can easily be spread. The use of protective barriers such as nets and covers are also a good option for preventing infestations.
Phytosanitary treatments
The aim is to provide the plant with maximum protection during the earliest stages of the crop, thus preventing any whitefly from getting established. It is in these earliest stages that a viral infection will cause the greatest damage as the virus will spread throughout the plant and will show all its symptoms as the plant begins to produce blossom and fruit. This is why insecticides are applied to the seeds in some crops. These act systematically as soon as the seedling starts to grow and continue to protect it for several weeks.
In later stages, insecticides can be applied to the leaves to ensure the protection for the longest possible time. It should be noted that the use of non-systematic ingestion insecticides is not usually effective in combating whitefly in its larval stage, since many of the larva lack mobility. The use of insecticides that act by physical means are also a good choice to fight this larval stage.
Whitefly Pest
Hosts:
Recorded on plumeria and 38 genera of plants from 27 plant families and over 100 different species.
Common on plumeria, vegetables, ornamental, fruit and shade tree crops in Hawaii, including avocado, banana, bird-or-paradise, breadfruit, citrus, coconut, eggplant, kamani, Indian banyan, macadamia, mango, palm, paperbark, papaya, pepper, pikake, poinsettia, rose, sea grape, ti, and tropical almond.
Distribution:
Native to Central American and the Caribbean region. First reported in Hawaii in 1978 and now present on all of the major islands.
Damage:
- Direct – damage caused by piercing and sucking of sap from foliage. Majority of feeding done during the first three nymphal stages. Usually insufficient to kill plants.
- Indirect – damage due to accumulated honeydew and white, waxy flocculent material. The honeydew serves as a substrate for sooty mold, which blackens the leaf and decreases photosynthesis and plant vigor, and can cause disfigurement. The flocculent material is spread by the wind and can create an unsightly nuisance.
- Virus transmission – damage from virus transmission can be considerable. These viruses cause over 40 diseases of vegetable and fiber crops worldwide.
Management:
This insect thrives in warm, dry weather. Heavy rains and cool temperatures may reduce populations.
- Non-chemical control – five natural enemies were introduced into Hawaii from the Caribbean to control whitefly populations. One of the three coccinellid beetles (ladybugs) has proved effective with high population densities of whitefly. Two parasitic wasps have proven effective against low populations of whitefly. These biological controls generally provide adequate control to minimize damage to plants.
- Chemical control – contact and systemic insecticides recommended for other pests on the same plant hosts may temporarily reduce whitefly populations. However, such insecticides may also harm whitefly predators and so should be avoided where possible.
The Spiraling Whitefly (Aleurodicus dispersus) has proven to be a nuisance and have caused damage to plumeria and native vegetation.