Description
Encarsia formosa and Eretmocerus eremicus are tiny parasitic wasps that attack whitefly. Encarsia was the first biological control agent for use in the greenhouse, developed in the 1920’s. Encarsia adults are black with yellow abdomens, less than 1/20th inch long. Larval stages live entirely inside immature whiteflies, which darken and turn black as Encarsia develops. Eretmocerus are pale lemon yellow with green eyes and clubbed antennae. They are native to southern Arizona and California and well adapted to hot climates. When Eretmocerus parasitize a whitefly scale it turns yellow.
Target Pest
Encarsia targets greenhouse whitefly (Trialeurodes vaporariorum) but can also parasitize silverleaf whitefly (Bemesia argentifolia) and sweet potato whitefly (Bemesia tabaci) at higher rates. Eretmocerus targets the sweet potato whitefly. Encarsia will directly feed on 3-4 L1s/day, whereas Eretmocerus are much more aggressive and will feed on 20-30/day.
Life Cycle
Both parasitoids have similar life cycles, which take about 15 days at 77°F, 28 days at 70°F, and 45 days at 59°F. Encarsia populations are all female (males sometimes occur but they are not functional). Eggs are laid in 2-week-old whitefly scales (second and third whitefly larval stages), one egg per scale. Females can lay up to 10 eggs per day for an average of 200 eggs. Larvae develop inside the whitefly scale for 10 days at 68°F They pupate for another 10 days, then adults emerge by chewing a hole in the top of the scale. Adults are most active for about 10 days, although they can live up to 30 days. In addition to parasitizing them, Encarsia and Eretmocerus kill whitefly scales by feeding on the host directly. They also feed on whitefly honeydew.
Monitoring Tips
Check the undersides of lower leaves for parasitized whitefly scales. They turn black (for greenhouse whitefly) or transparent brown (for sweet potato whitefly) so are easy to tell from unparasitized scales, which are white/clear.
Use in Biological Control
- Encarsia are effective controls for greenhouse whitefly on greenhouse cucumbers, tomatoes, peppers and poinsettias. They can control silverleaf/sweet potato whitefly, but only under optimum management using high release rates.
- Optimum conditions are temperatures over 68°F with high light levels and relative humidity 50-70%. When daytime temperatures are less than 64°F Encarsia activity is sharply reduced, making them less effective.
- Do not attempt to use Encarsia if high whitefly populations are already established. The beetle Delphastus is good for these situations and avoids feeding on parasitized whitefly making them compatible with both Encarsia and Eretmocerus.
- Dicyphus hesperus may be used with Encarsia and Eretmocerus and both wasps may be used together.
- For long-term crops, like vegetables, whitefly control is best achieved by establishment of the wasps (parasitism). In short term crops like ornamentals host feeding plays the biggest role in controlling whiteflies.
- Adult wasps of both species are good searchers and can easily find whitefly. Eretmocerus are more tolerant of high temperatures and host feed more.
Product Information
Encarsia and Eretmocerus pupae are sold glued onto cards or as loose scales. For pupae on cards, it is important to hang the cards from lower leaves in the shade as the wasps tend to fly upward. Avoid wetting them while watering. Place in hanging baskets as well as on plants on benches. Adults will emerge from the pupae over a period of 1-2 weeks at 68°F. Small emergence holes in the pupae are visible using a 10x lens and indicate that the parasite has emerged. If necessary, the Encarsia pupae can be held for up to 2 weeks at 40-50°F however, the percentage of emergence and searching ability will decrease with time
Introduction Rates
- 1-10 Encarsia/10ft2. Or 1-5 Encarsia /infested plant, every 1-2 weeks for at least 5 introductions, or until 80% of whitefly scales are parasitized. Same for
- In commercial greenhouses, Encarsia are usually released in low numbers before pests are present or in higher numbers after pest populations are established.
- Note! Above rates for Encarsia must be at least doubled for control of silverleaf and/or sweet potato whitefly or if temperatures are less than 64°
- Encarsia tend to remain in regions where the whitefly is concentrated, therefore it is important to distribute them well throughout the greenhouse.
- Take special care not to touch the pupae on the cards as they are extremely delicate. Hang cards on middle to upper branches of the plant. Use preventatively.
For Best Results
The whitefly species in a crop must be correctly identified to make sure it is a species that Encarsia can control and to determine the correct release rate. Eliminate whitefly from alternate sources such as weeds or previous crops and cuttings before releasing Encarsia. High whitefly populations hinder movement of the parasite as does the presence of honeydew. Spray with water or insecticidal soap to help with this.
Using Chemicals
Encarsia and Eretmocerus are extremely sensitive to insecticide residues that may persist on plants as well as greenhouse surfaces.
Resources
Eretmocerus eremicus Cornell University