Whitefly control with parasitic wasps
Whitefly is easy to treat with Encarsia parasitic wasps. Encarsia consists of cards loaded with parasitic wasp pupae of the species Encarsia formosa. These wasps are only 0.6 mm long, so they are probably not what you think of when you think of wasps. They are so small that you would never even know they are around, unless you know what to look for. They can only be seen with a trained eye or underneath a microscope, and look nothing like an ordinary wasp. They are harmless to humans.
Encarsia formosa uses whitefly to complete its life cycle. The parasitic wasps lay their eggs in whitefly nymphs. Inside the body of the whitefly, the wasp feeds and develops. During this time, the whitefly exists in a kind of zombie state before it finally dies. When ready, the new wasp emerges from the whitefly carcass in order to lay eggs in a new whitefly nymph. Since it is the whitefly nymphs that are parasitized, affected whitefly are unable to reach adulthood and therefore have no chance to reproduce.
A great majority of Encarsia wasps are female. Each female lays about 10 to 15 eggs per day and lives 2 to 3 weeks under optimal conditions. One Encarsia egg will kill one whitefly nymph. The cycle of parasitization will continue for as long as temperatures cooperate, or for as long as there are still whitefly nymphs present. This cycle is one of the best known examples of biocontrol, and its is highly effective. Encarsia is suitable for use in the organic garden and is harmless to the environment.
How to use Encarsia for whitefly
Encarsia is very easy to use. Hang the cards in the plants immediately after receiving them. Make sure that the cards do not get wet during the first few days and hang them with the back facing the sun. A few days later, the Encarsia parasitic wasps will automatically emerge from the pupae on the cards. They will immediately search the vegetation for hosts to parasitize. The empty pupae remain on the card or may fall off because of the heat.
It is best to use Encarsia at the beginning of a whitefly infestation so that the whitefly does not get the chance to develop faster than Encarsia (read about temperature below). Also, since the sapsucking whitefly excrete honeydew onto plant leaves, the leaves become sticky over time and hinder Encarsia's movement.
After treating with Encarsia, be careful when removing leaves from your plants (e.g. when harvesting a tomato crop), because there is a chance you will also remove parasitized nymphs.
What to look for
You will not notice a visual difference on the cards after the Encarsia pupae have emerged. After releasing Encarsia, you will only start to notice parasitized whitefly on the underside of the leaves after two weeks. The parasitized whitefly nymphs are easy to notice because they turn black, in contrast with the white color of unaffected whitefly.
Temperatures for Encarsia
Encarsia is found in warm regions around the world. They can be used in our climate in greenhouses or indoors, or during the summer outdoors. They need a minimum of 18° C during the day to act effectively and 6° C at night to avoid dying. The ideal temperature for development is 22°C.
While a female Encarsia lays an average of 10 to 15 eggs per day and lives two to three weeks under optimal conditions, the life span decreases considerably at higher temperatures. Temperatures that are too warm, i.e. above 28°C, are to the disadvantage of Encarsia parasitic wasps. At high temperatures, parasitic wasps have a shorter life span, which means that they can lay far fewer eggs.
Whitefly, in contrast, prefers high temperatures and is able to reproduce more rapidly when it's warm. When this happens, whitefly populations will grow faster than those of Encarsia and the infestation will grow instead of recede. For this reason, we advise to use Encarsia at the beginning of a whitefly infestation, especially if it is already summer at the time. As soon as you notice whitefly, you should hang Encarsia cards.
Liming the greenhouse or putting up a shade cloth are ways to keep the temperature in the greenhouse at a more acceptable level.
What does Encarsia eat?
Adult Encarsia parasitic wasps feed on honeydew excreted by whitefly, as well as on the body fluids of whitefly nymphs in their first and second stages. First- and second-stage whitefly nymphs are the food of choice for adult Encarsia wasps. They lay their eggs in the third and fourth nymph stage whiteflies, so they interrupt the whitefly life cycle at several points.
Combining with sprays
We do not recommend using sprays of any kind in combination with Encarsia. If you have already sprayed a chemical or natural product, you can contact us to check if there are still harmful residues that may affect Encarsia and how long we recommend waiting before placing an order.
Quantities
Available for 30 m², 150 m², and 300m², which works out to 1000, 5000 and 10.000 pupae respectively. The quantity you should release depends strongly on the stage of the infestation and the weather conditions of the moment. If the infestation is already very advanced, first remove the most infested leaves and then release Encarsia.
Encarsia Tips
- Start treatment at the first signs of whitefly
- Avoid honeydew build-up on leaves
- Shade or heat your greenhouse or veranda, depending on temperatures.
- Prune away heavily affected leaves before starting treatment
Whitefly in beech hedge
In beech hedges, the woolly beech aphid is often mistaken for whitefly, as they have a similar appearance. Beech hedges are not particularly prone to whitefly infestations. In your beech hedge, it is much more likely that you are dealing with the woolly beech aphid than whitefly. In that case, treating with Encarsia will have no effect.
For dealing with woolly beech aphid, the correct product to use is Chrysopa. If you are unsure which pest you have in your plants, please contact us for further advice.
Need advice? Have questions?
Would you like some advice on the best treatment for your specific situation? Please feel free to contact us. You can send us photos of your plants so we have a better idea of the infestation. We have more than 30 years of experience with using biological control in the organic garden, and we are happy to help you.