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Description and Biology

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Encarsia formosa is a wasp less than 1/16 inch long that parasitizes greenhouse whiteflies, silverleaf whiteflies, and others (but is harmless to humans). The head and thorax are dark brown and the abdomen is light cream to yellow. Males are completely dark and are rare. First described from Colorado, it now has a cosmopolitan distribution because of releases into greenhouses worldwide. When searching for prey, Encarsia formosa walks over the tops, edges, and bottoms of the whitefly's host plant. Upon finding a suitable whitefly nymph, this parasite either injects an egg into the nymph or punctures the nymph and drinks hemolymph that oozes out. Host feeding often kills the immature whitefly. Encarsia formosa feeds on all immature stages except the egg, but it prefers second stage nymphs and pupae. Encarsia formosa also sips honeydew excreted by the whiteflies. Females lay five to ten eggs each day although older Encarsia formosa lay fewer. The wasp grubs hatch and mature into a new generation of adults into about three weeks. Adults chew a conspicuous hole in the upper surface of the dead nymph. Parasitized greenhouse whitefly nymphs turn black. Parasitized silverleaf whitefly nymphs darken slightly. Each Encarsia formosa kills about 95 whitefly nymphs during its life either by feeding or oviposition. Encarsia formosa seems to be a warm weather insect that is less effective below 75o F. Insecticidal soap can be used to kill adult whiteflies without killing Encarsia formosa grubs inside whitefly nymphs. Insecticidal soap does not leave a toxic residue, so it could be used the day before releasing Encarsia formosa without fear of harming these parasites.

Encarsia formosa

Encarsia formosa parasitoids are very small wasps.

Encarsia formosa parasitoid

Encarsia formosa parasitoids search for prey by crawling about.

n pierce whitefly nymphs

Encarsia formosa parastiods often pierce whitefly nymphs and feed on their hemolymph.

Greenhouse whitefly nymphs turn black

Greenhouse whitefly nymphs turn black when infested by Encarsia formosa grubs.

A dead greenhouse whitefly nymph

A dead greenhouse whitefly nymph and an exuviae killed by Encarsia formosa.

Encarsia formosa parasitizes at least 15 species of whiteflies on hundreds of ornamental, vegetable, and weed host plants.

A healthy greenhouse whitefly nymph.

A healthy greenhouse whitefly nymph.

Healthy silverleaf whitefly nymphs are clear yellow.

Healthy silverleaf whitefly nymphs are clear yellow.

Residential Recommendations

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Encarsia formosa is available commercially. To use Encarsia formosa for biological control, there must be a resident population of whiteflies, otherwise these parasites disperse or die. If the whitefly population is severe, Encarsia formosa can be mass released as a “living insecticide,” but if whiteflies are scarce or moderately abundant, it can be released in small amounts to assure adequate suppression. Once a population of Encarsia formosa is established, it itself may become the victim of hyperparasites such as Signiphora coquilletti, Encarsia pergandiella, and Encarsia tricolor. Should the number of whitefly adults become too abundant, insecticidal soap can be applied without killing immature Encarsia formosa inside the parasitized whitefly nymphs (and without killing healthy whitefly nymphs as well). Because insecticidal soap does not leave a toxic residue, it can be used the day before Encarsia formosa are released without harm to the parasites.


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This Factsheet has not been peer reviewed.


Professor Emeritus
Entomology and Plant Pathology

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Publication date: March 8, 2017
Revised: Dec. 21, 2021

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