Encarsia formosa

Encarsia formosa is used all over the world for commercial control of whitefly on greenhouse crops. Commercial use began in Europe in the 1920s, but by 1945 interest had waned due to the development of pesticides. After 1970, the use was resumed and increased from 100 hectares of greenhouse crops to 4,800 hectares by 1993. Encarsia formosa has a cosmopolitan distribution due to getting into greenhouses all over the world, and its natural range remains uncertain.

Victims and cultures

Encarsia formosa parasitizes at least fifteen species of whitefly from eight genera. The most popular victims of the parasitoid wasp in our regions are greenhouse and tobacco whiteflies. The main greenhouse crops in which Encarsia is used are the traditional tomato and cucumber. Also, the parasitoid has proven itself well in areas with aubergines, gerberas, poinsettia, marigolds, and strawberries. Encarsia is recommended to be used in combination with Eretmocerus, especially in hot conditions. Eretmocerus also shows good resistance to some pesticides. For tomato and aubergine crops, it is recommended to add an assistant in the form of Nesidiocoris tenuis to this pair to achieve better results.

Description and life cycle

The females of Encarsia formosa are small, about 0.6–0.7 mm in length. The head and thorax of the insect are black, and the abdomen is yellow. Males of the species are in the minority and are rare, they differ in completely black colour.

Encarsia lay eggs inside the whitefly when it is in the nymph or pupal stage. When the egg of Encarsia hatches, the larva of the parasitoid wasp begins to feed inside the nymph, causing its death. Pupation of Encarsia formosa larvae also takes place inside the infected whitefly nymph. During the pupation of the wasp, the nymph of the whitefly turns black. A few days later, a new adult wasp emerges from the infected nymph to complete the cycle. Almost all adult wasps are females (> 99%). The development time from egg to new adult wasp varies from 31 days at 18 °C and up to 10 days at 30 °C. Development does not occur at temperatures below 10 °C, and temperatures above 38 °C can lead to the death of wasp larvae.

Adults also kill whitefly nymphs by feeding on them. Imago Encarsia formosa live for 15-39 days and during this time lay up to 300 eggs.

Encarsia formosa usually lays 8-10 eggs per day, but the daily rate of maturation and egg laying decreases with the age of the wasps. Adult individuals of wasps receive energy and nutrients by consuming the fall and hemolymph of the hosts, penetrating them with an ovipositor, but not laying eggs at the same time. Encarsia formosa feeds on all pre-imaginal stages of the whitefly, except the egg, but prefers nymphs and pupae of the 2nd age. Nymphs that were used for feeding are not used for laying eggs, and previously infected whiteflies are not used for feeding hosts.

The vast majority of females, as representatives of the species, are due to telitokia (parthenogenetic reproduction, in which only females reproduce). For Encarsia formosa, this is mediated by the bacterial infection Wallachia. Exposure of females to antibiotics or high temperatures (31 °C) for two or more generations suppresses microbial activity, allowing females to successfully produce male offspring. After the destruction of symbionts, fertility decreases. Males develop as primary whitefly endoparasitoids. When describing the mating behaviour of Encarsia formosa, it is indicated that males cannot qualitatively inseminate females.

Encarsia formosa can be introduced into all cultures affected by whitefly. To achieve the best results, as a preventive measure, the release of entomophage should be started at the beginning of each new harvest. Alternatively, you can control the level of whitefly using yellow sticky traps and release parasitoid wasps at the first sign of whitefly. It is necessary to continue weekly releases until the formation of the parasitoid population. If possible, it is advisable to adjust the temperature to 23-27 °C, humidity to 50-70%, and also set the daylight for at least 10 hours to promote the development of Encarsia formosa.

If there are ants on the site, then they should be given special attention. The ants will protect the whitefly from predators and parasites in order to preserve their food source in the form of paddy secreted by the pest. If there are no ants on your site, make sure that the honeydew is not “too heavy.” This can be an obstacle to the work of parasitoids, because they will spend too much time cleaning, which will slow down their movement and search for victims.

Recommendations for implementation

Recommended application rates will vary depending on the type of crops, as well as on the time of year and the pest population. The general recommendation is to release at the rate of 1 individual of Encarsia formosa per 1 square metre weekly until an adult whitefly appears, and then double the number of released parasitoid wasps. It is necessary to monitor the back of the leaf for the presence of black nymphs, and when 80-90% of them are black, you can reduce the number of applications. It is important not to remove the black scales before the entomophage appears from them, as this will affect the formation of the Encarsia formosa population.