Encarsia formosa and Delphastus pussillus: a golden combination in ornamental horticulture!

The effectiveness of the parasitic wasp Encarsia formosa in controlling the greenhouse whitefly has long been known, in fact since 1926. This parasitic wasp was one of the first natural enemies introduced commercially – and successfully – into modern horticulture.

After having proved itself for a great many years as a useful parasite in greenhouse horticulture, in recent years it has also been used successfully in various ornamental crops such as rose and gerbera. However, these are year round crops, which require a different approach.

Wesley Akkermans, Crop Protection Specialist at Arend-Sosef (the Netherlands): “This parasitic wasp is mainly active by day, which means that it is less active in the winter months with its shorter days and low light intensity. It is therefore important to support the parasitic wasp in early spring by turning off sulphur evaporators and each week introducing 4 to 6 parasitic wasps per m2. Depending on the whitefly level this should be repeated every 4 to 6 weeks.”

Encarsia formosa is a parasitic wasp that can parasitize all the larva stages of whitefly, but mainly prefers the 3rd and early 4th stage. It is therefore advisable to complement Encarsia formosa,with the use of predators that attack other stages of the whitefly life cycle. In addition to the predatory mite Amblyseius swirskii, also Delphastus pussillus is often used.

Wesley Akkermans: “Together with Biobest we are now advising growers to start using more Delphastus pussillus. The use of this species is turning out to be a success. Delphastus pussillus is a small ladybird which feeds on all stages of whitefly, but above all prefers whitefly eggs and larvae. The little beetle does not go into diapause during short day conditions and as a result is already active early in the season. Both the larvae and the adult beetles are excellent predators and can consume considerable quantities of eggs and larvae a day. The adult beetles are active flyers that home in on the odour given off by young whitefly, making them particularly suited to track down whitefly breeding places in the crop.”
Delphastus pussillus larvae move slowly from plant to plant via the leaves. To develop a good population Delphastus pussillus needs sufficient whitefly, so it is advisable to only introduce these beetles locally in whitefly hotspots. Do this for a period of at least 4 weeks or until the first larvae are found.

Wesley Akkermans: “Integrated whitefly control is still custom work but with the combination of parasitic wasps and predatory beetles we are able to control whitefly effectively!”

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