Whitefly control

Encar-line f

Encarsia formosa

  

 

How does it work?

The pupae attached to the card produce adult female Encarsia for at least a week or longer after they are hung in the crop. Each of these wasps then moves through the crop searching for whitefly larvae (also known as ‘scales’). When a larva is found, the female wasp carefully examines it, palpating it with her antennae to find out if it is the right type of whitefly and the of an right appropriate size to support her offspring. If it is correct, she lowers the tip of her abdomen onto the larva, and carefully inserts an egg into it. When the Encarsia egg hatches, it consumes the whitefly from within. Initially it feeds without killing its host, so that the whitefly continues to feed and grow, but as the host larva reaches maturity and ceases to feed, the parasite attacks the vital organs. At this point the whitefly scale turns black, and about eight days later a new Encarsia emerges to repeat the process.

Almost all individuals of Encarsia formosa are female. Males do occur, but are rare and are thought to serve no purpose. They can be distinguished from the females by having a black or dark brown abdomen, rather than the bright yellow abdomen, which is such a distinctive feature in the females.

The female will kill more whitefly than she parasitises. Females prefer to lay eggs in third and fourth instar larvae, but if the host larvae she encounters are too small she may still attack them with her ovipositor. Instead of laying an egg she will turn and feed on the body fluids thatwhich leak from the wound. This host feeding increases her longevity, and the number of eggs she can lay during her life. In many cases it will prove fatal to the whitefly.

Laboratory trials show that adult Encarsia can live for up to 21 days at 21°C, but in glasshouse conditions few will live for more than five days. Parasitised hosts turn black 11 or 12 days after being stung at this temperature, and a fresh Encarsia female will emerge 12 days later. At cooler temperatures the development time is longer.

When and where should you use it?

Encarsia formosa can be used as a protective treatment in any crop where the main pest is the Greenhouse Whitefly (Trialeurodes vaporariorum). It is most widely used in protected salad crops such as tomatoes, cucumbers, aubergines and peppers, but is also used successfully in many ornamentals. It should be released preventively, before the first whitefly are seen, and rates increased when the pest can be found. If whitefly populations become established before Encarsia are introduced, it is better to use a compatible chemical to reduce the population. While it is still possible to gain control with Encarsia, this is not usually cost effective because of the high rates required.

How should you use it?

The Encarsia cards will be delivered in boxes containing strips of five cards. Take these into the crop, and carefully separate the strips into individual cards by folding then tearing along the perforations. Take great care not to handle the pupae themselves, which are in the recess at the base of the card.

Hang the cards onto the leaf petioles of the plants, where they will be shaded from full sun. You should distribute the cards as evenly as you can throughout the crop, but it is quite reasonable to hang cards in alternate rows rather than in every row, to reduce the time taken for the job. If you do this, try to place the cards in different rows the following week.

Recommended introduction rates will vary depending on the crop species, as well as on the time of year and population of the pest, but a general recommendation is to release at the rate of 1 card per 120m²0.5/m² weekly until adult whitefly are seen, and then increase the rate to 1 card per 20-60m²between 1 and 3/m² each weekeach week. Monitor the lower leaves for the presence of black scales, and when 90% of those present are black, reduce applications. It is important not to remove the black scales before they have emerged, as much of the control relies upon the Encarsia whichthat are breeding within the crop.

When should you not use it, and what are the control alternatives?

Do not use Encar-line f without making sure that the whitefly you have are Trialeurodes vaporariorum. If the main population is Bemisia tabaci, you should use Eretmocerus eremicus as the main parasite. It is simple to distinguish the two whitefly species from each other. Trialeurodes adults rest with their wings folded over the body and completely covering it. They have a triangular outline. Bemisia adults hold the wings at the side of the body, and the yellow of the body can be easily seen. They have a more rounded outline, and are smaller. Larvae of Trialeurodes are oval in shape,, and when nearly fully grown they become quite thickened, so that they have almost vertical sides. They are a translucent white in colour. Bemisia larvae are always flattened to the leaf, and the posterior end tends to be more pointed. They are normally a pale yellow colour.

If populations of whitefly are high, you should make a treatment with a compatible chemical to reduce pest populations before introducing beneficial insects. There are a number of insecticides available thatwhich can be used without disrupting other elements of a pest management programme.

Syngenta Bioline also produce Eretmocerus eremicus, Eretmocerus mundus and Macrolophus caliginosus for control of Bemisia tabaci and Trialeurodes vaporariorum. Eretmocerus can be used alone or together with Encarsia, and is of particular valueuse at higher temperatures. Refer to the product information about these beneficials for more details on their use.

What will it do?

When used as recommended, Encar-line f will prevent the development of populations of the Glasshouse Whitefly (Trialeurodes vaporariorum) to damaging levels. It will not normally eradicate the pest, and it is not intended to do so.

What won’t it do?

Encar-line f will not control large existing populations of whitefly at economic release rates. Although it can be used against Bemisia tabaci in some crops, Eretmocerus is a better alternativemore appropriate. Macrolophus is also suitable for this purpose on round tomatoes and aubergines.

Trials in Spain have shown that Encarsia is not effective in the growing conditions in the south of that country. It is not currently known if this is also the case in other regions with Mediterranean type climates.

Chemical compatibilities.

Many insecticides can be successfully combined with Encar-line f. There are a number of chemicals, which disrupt development of the whitefly larvae, and others that which can be used to control or adjust populations of pests such as leafminer, aphid and Lepidoptera without killing Encarsia formosa. Control of thrips is more problematic, as there are few compounds currently on the market for thrips control thatwhich do not disrupt the use of other beneficial arthropods.

Programme compatibilities.

Encar-line f is compatible with all other beneficial mites and insects used in our crop programmes. When used with Macrolophus caliginosus releases of Encar-line f. should cease once Macrolophus is established.