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Eretmocerus-W (Eretmocerus warrae) - greenhouse whitefly parasitoid

Target pests: Greenhouse whitefly, Trialeurodes vaporariorum.

Eretmocerus

Eretmocerus warrae is a small, parasitoid wasp which is believed to be native to Australia and New Zealand. It has not previously been commercialised. It occurs widely across the southern half of Australia on a variety of crops and weeds. Trials in 2009/2010 indicated it had good potential against greenhouse whitefly in greenhouse crops, particularly tomato. It was commercialised in Australia in 2010 by Biological Services, being found on a range of crops including tomato, eggplant and strawberry, and in many locations in W.A., S.A., Vic., N.S.W and Tasmania.

Little is known about the range of whitefly species which Eretmocerus warrae attacks but it does not control silverleaf whitefly, unlike the closely related species E. eremicus overseas. The taxonomy requires further investigation. Eretmocerus warrae is supplied as parasitised greenhouse whitefly pupae on cards, or as loose pupae in vials. A minimum of 100 Eretmocerus wasps should emerge from each card. Eretmocerus is more expensive to produce than Encarsia but its greater tolerance of conditions of high and low temperature and low humidity, and will be very useful as a control supplement during periods when Encarsia are not sufficiently active especially in the middle of summer.

Life history and biology

Eretmocerus warrae is a tiny wasp <1 mm long, a little larger than Encarsia, and completely yellow except for three distinctive red ocelli on the top of the head arranged in a triangle. They are winged and can travel several hundred metres in a day, possibly wind assisted. Males are very rare. The life-cycle has not yet been studied in detail. The female targets 1st and 2nd stage whitefly nymphs (mostly 2nd) for egg laying, depositing a single egg under but not into the ventral surface of the whitefly nymph. Encarsia targets 3rd and 4th stages so the two species are complementary rather than competitive. On hatching, after (~4 days), the tiny larva bores into the whitefly nymph over the next 3-4 days and waits until the whitefly pupates. It then releases digestive enzymes which dissolve the whitefly innards which are used by the wasp larva to complete development. There are three parasitoid larval stages, with development from egg to adult taking about 14-28 days, depending on temperature. Unlike when parasitised by Encarsia, the whitefly body does not turn black, so careful checking with a magnifier is necessary to confirm parasitisation. The whitefly body turns yellow/brown with red to greeen eyes visible within the whitefly shell just prior to emergence. The adult parasitoid cuts a circular emergence hole in the upper shell. Most eggs are laid early in the life of the female (~150 in total), which lives only 1-2 weeks, so it is important to place this parasitoid close to suitable hosts to avoid wasting time and energy in searching. Host feeding on older, non-parasitised whitefly nymphs is an important source of nutrients for the female for maximum egg production and contributes to control of the whitefly.

Crop usage

Eretmocerus-W is still being evaluated but it is anticipated that it will be a useful supplement to Encarsia in all crops where greenhouse whitefly is a pest, particularly under more extreme environmental conditions. Leaves with some hairs force the border of whitefly nymphs to grow around the hairs, facilitating insertion of the parasitoid egg under the rim. However, leaves that are very hairy may inhibit parasitoid movement. Crops that may benefit from Eretmocerus use include greenhouse vegetable (tomato, cucumber, eggplant), ornamental (gerbera, chrysanthemum, rose), strawberry and herbs. In summer and in warmer climates they may also be useful in outdoor nursery stock and gardens.

Environmental preferences

Eretmocerus-W is a warm-temperate parasitoid which tolerates (but is unlikely to prefer) extremes of high and low temperature and low humidity. Its preferred range has not yet been studied but it should be useful within a range of 15-35°C, and will survive at temperatures less than 10°C and over 38°C.

Application information

Storage and handling: Eretmocerus-W can be stored for a few days at 6-10oC if necessary but emergence and parasitisation rates may be reduced if kept longer. Eretmocerus are sent as parasitised whitefly pupae glued to the centre of cards joined in sheets or as loose parasitised pupae in vials. At least 100 adult wasps should emerge from each card. The number of scales per card are >100 in case some fail to emerge. Avoid handling the parasitised scales in the centre of the card.

Release method(s): Cards should be separated in the greenhouse and hung individually from leaf petioles in the shade near whitefly colonies about 30cm below the top of the crop. Cards should be placed as soon as possible. The number of emerged adults during transport should be minimal. If provided as loose pupae, place these in specially designed bug boxes near whitefly colonies, or sprinkle on leaves in shade and not exposed to overhead irrigation. Do not place on the ground or ants will eat them. Ants may need to be controlled as they may target pupae on cards. Apply randomly through the crop if whiteflies have not yet been observed, or in close proximity to known infestations if these are already present.

Timing of application: Eretmocerus-W should be used preventatively to stop whitefly build-up. Releases are best made weekly in susceptible crops prior to whitefly invading, or at the very first sign of them in the crop, or on yellow sticky traps. They should continue to be released until they are well established on any pest populations in the crop. Note it may take 3-4 weeks following first releases before first parasitism is visible. Host feeding in itself may significantly reduce whitefly populations. Yellow sticky traps are a good indicator of whitefly presence in the crop.

Release rates: Release rates will vary depending on the attractiveness of the crop and the temperature of the greenhouse. Suggested release rates are 0.5-1/m2 weekly as a preventative treatment, increasing to 2-3/m2/week for at least 4 weeks once whiteflies have been detected. Release 10/m2 into hotspots. Control is not immediate, therefore, spot-treatment of whiteflies in hot-spots with a low toxicity, short-residual pesticide is recommended to prevent migration through the greenhouse, may be required.

Monitoring control success

Examine under sides of older leaves where greenhouse whitefly colonies are present for parasitised pupae 3 weeks after the first Eretmocerus-W release, using a 3x headband magnifier for quick scanning, and a 10x magnifier for closer inspection. Check the lower leaves of the plants in the vicinity of adult activity to locate whitefly pupae to check for parasitism. The time for pupal development and continued growth of the crop, means the lower and older leaves are where the parasitised pupae are located. Emergence holes should follow in another 1-2 weeks. Holes should be round and visible if held up to the light. Yellow parasitoids should be visible actively feeding on and parasitising nymphs. They are sometimes seen flying/hovering in high numbers in the top of the crop on warm sunny days when well established. Keep yellow sticky traps away from release sites as they catch Eretmocerus.

Tips for best results

Use preventatively, before whiteflies are observed in the crop. Release close to whitefly colonies with young nymphs where possible. Eretmocerus-W is best used to supplement Encarsia during periods when this parasitoid is less active (high and low temperatures, low humidity). The presence of ants attracted to honeydew or sooty mold can be an indicator of whitefly hot-spots. Knock back any heavy whitefly infestations and reduce honeydew with compatible pesticides, even water spray, before releasing Eretmocerus-W. If parasitism rates are very low, have the whitefly species identified or suspect pesticide residues. Bait ants as they are disruptive to beneficial insects.

Quality control

Batches are held and checked by Biological Services, but problems during transport may affect viability. Parasitised whiteflies are shipped close to emergence time, so some parasitoids may emerge in transit. Check that these wasps are alive. Dead wasps may indicate unsuitable conditions in transit. In most instances no wasps will have emerged at receipt. Hold one card in a jar at room temperature until some emergence occurs to check viability, but release the rest as soon as they arrive.

Pesticide compatibility

Adult Eretmocerus warrae appear less sensitive to pesticides than Encarsia formosa but definitive studies have not yet been conducted. Parasitoids are generally more sensitive than predators. Contact Biological Services for current information. Overseas data for Eretmocerus eremicus can serve as a guide but there may be differences between species and even strains from different sources depending on exposure history. Parasitoid stages within mummies are more resistant to pesticides but may be affected in early development. The strain that has been developed was collected from a hot/dry district, where insecticides were regularly used.

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Technical resources

Eretmocerus technical sheet (134 kb)