Are whiteflies infesting your greenhouse? If so, the natural predator of whiteflies, the parasitic wasp Encarsia formosa, could be an excellent solution to your problem – if you react fast.
Not all wasps are harmful to humans. In fact, some are quite beneficial. The parasitic wasp Encarsia formosa is one of the many beneficial insects that are best to use in enclosed spaces like greenhouses. Read on to find out all you need to know about Encarsia formosa and other biological controls and natural ways of combatting whiteflies.
Tip: There is a large variety of parasitic wasps that prey on many different insects. The Trichogramma genus of wasps, for instance, parasitise many different types of moths including the clothes moth (Tineola bisselliella), and the three main pantry moths, which are the Indian meal moth (Plodia interpunctella), the Mediterranean flour moth (Ephestia kuehniella), and the warehouse moth (Ephestia elutella). For more information on identifying, preventing and controlling pantry moths and clothes moths, read our in-depth articles on the subjects. That said, Trichogramma wasps do not parasitise garden pests like whiteflies.
The parasitic wasp Encarsia formosa is a member of the Aphelinidae family and is classified in the same order as bees and wasps, Hymenoptera. Unlike common bees and wasps, however, Encarsia formosa are completely harmless to humans. They are very tiny insects, with adults growing to a meagre 0.6 mm tall and 0.3 mm wide. Adult female Encarsia formosa have a yellow abdomen with a black thorax and head. Whilst they are rarely found, the adult males are all black in colour. They are an interesting species of insect, as sexual reproduction is rare. Most reproduction is through thelytokous parthenogenesis, whereby female offspring are produced from unfertilised eggs, a process which is regulated by bacterial infections by Wolbachia species.
In addition to feeding on whiteflies, adult Encarsia formosa also parasitise them by laying eggs in their hosts while the latter are in their immature stages. This results in the death of the host, making Encarsia formosa quite an effective biocontrol of whiteflies. Under optimal conditions, each female can lay up to five to 10 eggs per day and as many as 50 to 100 eggs during her lifetime. The eggs hatch, and all juvenile phases are spent inside the host, consuming it in the meantime. Around two weeks after the eggs have been laid, Encarsia formosa emerge from the host as adults.
In greenhouse production, Encarsia formosa have been used to control whiteflies for almost a century now. Encarsia formosa parasitise many species of whiteflies, but the two that cause the greatest economic damage in greenhouse cultivation are Trialeurodes vaporariorum and Bemisia tabaci.
Tip: In order to be effective, Encarsia formosa parasitic wasps need to be deployed early, as soon as you observe whiteflies on your plants. If you wait until whitefly infestations reach critical levels, Encarsia formosa wasps may not be able to make enough of an impact to save your crop.
Whiteflies are small, white, sap-sucking insects of the Aleyrodidae family. They cause extensive damage and crop loss by sucking the sap of their host plants. They can also cause damage to the plants with their excrement, known as honeydew. The honeydew that the whiteflies leave behind on the plant’s leaves can lead to outbreaks of a variety of fungal species known as sooty moulds. These sooty moulds then spread across the leaf surface, blocking light and restricting photosynthesis. Whitefly saliva is also toxic to the plant and, in large numbers, whiteflies can decimate a crop.
Tip: Because whiteflies are sap-sucking insects, and the adults are mobile and travel from plant to plant, another threat they pose is as disease vectors. They can spread diseases from plant to plant and from one area to another. While there are many natural predators of whiteflies in temperate climates, whiteflies thrive in temperatures between 20 and 30 °C. Therefore, it is still important to monitor and control infestations.
Whiteflies can infest crops in your garden or in your greenhouse. With a lack of natural predators in our homes, they can also be especially problematic on indoor plants. They can be found on both the top and bottom surfaces of leaves and occasionally on some fruit and flowers. It is important to recognise whiteflies and spot them on your plants before their numbers reach a level that is difficult to control.
Some whiteflies are host-specific, while others can attack a variety of different hosts. Here are a few of the more common whiteflies and their hosts:
- Aleurocanthus woglumi, the citrus blackfly, attacks citrus plant species. While black in colour, it is still classified as a whitefly.
- Aleurodicus dugesii, the avocado whitefly, as the name suggests, is a pest found on avocado trees.
- Aleyrodes proletella, known as the cabbage whitefly, is found on various Brassica species including cabbage.
- Bemisia tabaci, the silverleaf whitefly, is found on a wide variety of hosts. It is considered a pest on ornamental and agricultural crops alike, including tomatoes (Solanum lycopersicum), beans (Phaseolus vulgaris), cassava (Manihot esculenta), cotton (Gossypium spp.), cucurbits (Cucurbitaceae), potatoes (Solanum tuberosum), sweet potatoes (Ipomoea batatas).
- Trialeurodes vaporariorum, known as greenhouse whiteflies, is a major pest found in greenhouses. The greenhouse whitefly can infest a wide variety of hosts including ornamentals, vegetables, and fruits. The main susceptible crop hosts are cucurbits (Cucurbitaceae) and nightshades such as tomatoes (Solanum lycopersicum), aubergine (Solanum melongena), and potatoes (Solanum tuberosum).
When it comes to how to get rid of whiteflies, the most important thing to consider is which whitefly you are actually dealing with. Proper identification is required to determine effective control. Placed above plants, sticky traps such as our Plantura Yellow Sticky Traps are a great way to trap whiteflies in order to properly identify them. They are also great for monitoring the population levels of insects. Just be sure to replace the traps on a regular basis so that you can tell if an insect population is increasing or decreasing over time. This way, control methods can be implemented before populations reach a critical level, when preventative measures become ineffective. Quarantining new plants before you place them in your greenhouse or garden is an excellent practice to prevent whitefly infestations. These yellow sticky traps are a great way to detect insect pests in your quarantine area too.
As discussed earlier, Encarsia formosa parasitic wasps are most effective against the two species of whiteflies, Trialeurodes vaporariorum, and Bemisia tabaci, which are major pests indoors and in greenhouses. They are most effective at controlling populations of whiteflies when they are released in the early stages of infestation. For best results, follow these steps:
- Only use parasitic wasps in greenhouses, high tunnels, or indoors. Encarsia formosa are not effective outdoors as they may be consumed by predators, blown away by the wind, or die from exposure to non-optimal temperatures, humidity, or light.
- After receiving your Encarsia formosa parasitic wasps, release them promptly as they can only be stored for short periods before they start to lose viability.
- For best results, purchase enough parasitic wasps for your entire space, or cluster all infested plants in close proximity so the wasps can effectively control the whitefly populations.
- Encarsia formosa are normally shipped as eggs on a cardboard sheet, but there is a chance the eggs could hatch during shipment. It is therefore important to only open your packages of wasps near the plants that are infested with whiteflies.
- Encarsia formosa only thrive in optimal conditions. For best results, make sure temperatures are between 22 and 27 °C with humidity levels of at least 65%. They also need light to survive, so when using them indoors, it may be necessary to use supplemental lighting.
- Refrain from using any plant protection products as these could also harm your beneficial Encarsia formosa.
- After about 4 weeks, you should notice a reduction in your whitefly infestation. It is natural for the population of Encarsia formosa to dwindle over time, so it may be necessary to purchase and release multiple lots of the wasps for a prolonged control of whiteflies.
Since whiteflies are all sap-sucking insects from the same family, many non-chemical treatments like insecticidal soaps, horticultural oils, and plant-based treatments like neem and pyrethrum sprays, all provide short-term, temporary protection against these pests and therefore require multiple applications. These non-chemical treatments can also be harmful to Encarsia formosa, so, when it comes to treating whiteflies, early detection, monitoring population levels, combined with biological controls is the best solution.
Tip: Unfortunately, Encarsia formosa do not feed on or parasitise the cabbage whitefly, Aleyrodes proletella, so you will need to use other methods to tackle this pest. Another whitefly biological control is the black ladybird beetle, Delphastus pusillus, which preys on many species of whiteflies including Trialeurodes vaporariorum, Bemisia tabaci, and Aleurodicus dugesii. You can utilise black ladybird beetles in greenhouses, a low tunnel, or even in your garden.
Want to learn more about other beneficial insects? Check out our in-depth article on controlling aphids with the seven-spot ladybird.