What are whiteflies?
Greenhouse whiteflies (Trialeurodes vaporariorum) are white colored tiny insects that use their piercing and sucking types of mouthparts for causing damage to leaves. Whiteflies lay about 200 eggs on the lower surface of leaves. These eggs hatch within 7 days into small nymphs that develop through four stages (instars). The first instar individuals are called ‘crawlers’ because they crawl on plant surfaces to find permanent feeding sites on the leaves. Once they find feeding site, they enter into the flattened, legless and immobile second stages that continuously feeds on the leaf by inserting their mouthparts into leaf tissue for about 3-4 weeks. These nymphs then molt twice into the third and fourth stages and then form pupae. After 7-10 days, adult whiteflies emerge from pupae and the life cycle continues. Although adult whiteflies live only for a months but they can complete several generations during the growing season of host crops.
Damage caused by whiteflies
Whiteflies cause both direct and indirect damage to their host crops like vegetables, ornamental plants, fruits and several field crops.
In case of direct damage, both adults and nymphs suck cell sap from the underside of leaves by using their piercing and sucking types of mouthparts and causes symptoms like yellowing, drying and prematurely falling off leaves from the plants. Also, heavily infested plants can eventually die off prematurely.
In case of indirect damage, whiteflies while feeding generally secrete honeydew that stimulates the growth of black sooty mold on the surface of leaves. The black sooty mold covers the whole leaf and severely affects photosynthesis, a process in which plants convert light energy from sun into chemical energy for the synthesis of their own food. This black sooty mold also reduces the quality of the produce and aesthetic value of many ornamental plants. Whiteflies also transmit different types of plant viruses that can cause economic loss to the agricultural, horticultural and ornamental crops.
Control of greenhouse whiteflies with parasitic wasp Encarsia formosa
What are parasitic Encarsia formosa wasps?
Encarsia formosa are very small about 0.5 to 1 mm long endoparasitic wasps that are known to parasitize and kill both the larvae and pupae of various species of whiteflies.
How Encarsia formosa kill whiteflies?
Both the adults and larvae of Encarsia formosa can kill whiteflies by causing physical injuries and feeding internally on them. Briefly, adult wasps puncture the body of whitefly nymphs or pupae with their ovipositor and feed externally on the oozing blood (hemolymph) and the body content of the nymphs or pupae. Also, females of Encarsia formosa lay eggs using their ovipositor inside the body of adults and nymphs of whiteflies. After hatching from eggs, the wasp larvae will then start feeding internally on the body content of whitefly nymphs or pupae and eventually kill them.
How many Encarsia formosa should be released for the effective control of whiteflies?
Encarsia formosa wasps are commercially available as parasitized pupae of whiteflies. These parasitized pupae are adhered to a small card which can be hung in the plants. For the effective control of whiteflies, release 10-15 Encarsia formosa parasitized pupae per 10 square meter whitefly infested area but in heavily infested areas, they should be released at the same rate 3 to 4 times weekly. Release wasps early in the morning or evening when daylight level and temperature low and within 18 hours of receipt. However, if you are not ready to release them, you can store them in the cool place at 45-50°F (7-10°C).