Trialeurodes vaporariorum (whitefly, greenhouse)

Whiteflies are small Hemipterans that typically feed on the undersides of plant leaves. They comprise the family  Aleyrodidae, the only family in the superfamily Aleyrodoidea. More than 1550 species have been described.

In warm or tropical climates and especially in greenhouses, whiteflies present major problems in crop protection. Worldwide economic losses are estimated at hundreds of millions of dollars annually.

Prominent pest species include:

Although several species of whitefly may cause some crop losses simply by sucking sap when they are very numerous, the major harm they do is indirect. Firstly, like many other sap-sucking Hemiptera, they secrete large amounts of honeydew that support unsightly or harmful infestations of sooty mold. Secondly,they inject saliva that may harm the plant more than either the mechanical damage of feeding or the growth of the fungi. However, by far their major importance as crop pests is their transmission of diseases of plants.

The most prominent disease vectors among the Aleyrodidae are a species complex in the genus BemisiaBemisia tabaci and B. argentifolii transmit African cassava mosaic, bean golden mosaic, bean dwarf mosaic, bean calico mosaictomato yellow leaf curl, tomato mottle, and other Begomoviruses, in the family Geminiviridae. The worldwide spread of emerging biotypes, such as B. tabaci biotype B, also known as, ‘B. argentifolii’, and a new biotype Q, continue to cause severe crop losses which are expected to increase, demanding matching increases in pesticide use on many crops (tomatoes, beans, cassava, cotton, cucurbits, potatoes, sweet potatoes). Efforts to develop environmentally friendly integrated pest management systems, with the goal of reducing insecticide use, aim to re-establish the ecological equilibrium of predators, parasitoids, and microbial controls that were once in place.

WHITE FLY LIFE CYCLE

Eggs

Eggs are approximately conical in shape, yellowish-white turning to purplish grey after 2 days and 0.25 mm long. They are oviposited on a short pedicel, which is inserted in epidermal cells on the lower leaf surface, often in a circle or a crescent.

Nymphs

Nymphs or ‘crawlers’ are usually pale green, but can also range from yellow to dark brown. They are oval, flat and resemble scale insects. There are four or possibly five leg segments and two to three antennal segments. Segmentation is not clear and most specimens will appear to have only three leg segments and two antennal segments. Small amounts of powdery white wax are usually produced after the crawler settles and begins feeding. The first nymph is mobile, whereas later nymphal stages are immobile. They resemble soft scale insects, but have a vasiform orifice on the back through which honeydew is expelled. There are four nymphal stages with the final stage beginning as a feeding nymph before it becomes a pupa. The final larval stage begins as a flat translucent disc, but as it develops through to the pupa a waxy fringe begins to develop around the margin. As this grows, the larva becomes more ‘pork pie’ shaped.

Pupae

The pupa is the final stage of the fourth nymphal instar and is assumed to be at the point where the nymph stops feeding and apolysis begins. The pupa becomes a milky-yellow colour and, as the adult develops within, red eyes become visible through the cuticle. The marginal fringe, which is formed from many fused wax rods, is very obvious at this stage. Downward curving wax setae are also visible all around the edge of the marginal plain. On hirsute leaves, the pupae often develop long, waxy setae on the dorsal surface. These are not always present on pupae that have developed on glabrous leaves.

Adults

Adults are about 1.5 mm long, white and resemble tiny moths. The wings are pale yellow, held relatively flat when in repose and are coated with a pure white waxy bloom.

Hosts/Species Affected

The total world record of greenhouse whitefly host plants is approximately 859 species, belonging to 469 genera in 121 families.

Many species of plants grown under glass are liable to attack by T. vaporariorum. In temperate countries, the most severely affected crops are aubergine, cucumber, beans sweet peppers, tomatoes and a large number of ornamentals, including species of Fuchsia, Gerbera, Pelargonium, Solanum and chrysanthemums, poinsettias and primulas.

Insecticide resistance

The synthetic pyrethroids were the most effective insecticides for greenhouse whitefly control, when they were first introduced in the end of the 1970s. But after several years of application, whitefly control with both fenvalerate and deltamethrin became very difficult in glasshouses. In the late 1980s, buprofezin was used for whitefly control instead of pyrethroids. Recent sampling of populations of T. vaporariorum for insecticide resistance are described by Gorman et al. (1988) for Europe, Ortega Arenas et al. (1998) for Mexico and by Omer et al. (1993) for Hawaii, USA. Resistance to buprofezin and imidacloprid has recently been confirmed. 

So far little researches have been studied on the effect of plant compounds on whitefly. Todays there are many debates  about the use of chemical pesticides, which are expected new formulations based on plant compounds reduce significantly the problems involved.

It is hoped that by using this formulation, the pests resistance to insecticides will be reduced. In addition, beneficial insects are also less exposed to poison. There are various methods for producing insecticides and improving their performance, which nanotechnology is relatively newer and in the early stages of development. The purpose of this technology is to reduce the use of pesticides and control the release of toxin compounds in the environment. This method, which is associated with a slow release of the active ingredient, increases solubility, increased permeability, and especially the stability of the escaped compounds, and can reduce the usage dose. Therefore, the effect of nanoemulsions on the basis of herbal essential oils and biodegradable polymers such as Salipi pest has been successful in controlling whitefly in farm and agro-greenhouse environment.