Tip Top Bio-Control Technical Bulletin

Encarsia formosa
Whitefly Exterminator II

Target Pests:
Greenhouse whitefly (Trialeurodes vaporariorum); Silverleaf whitefly (Bemesia argentifolia);
Sweet potato whitefly (Bemesia tabaci).

Description:
Encarsia formosa is a tiny parasitic wasp that parasitizes whiteflies. It was the first biological control agent developed for use in greenhouses. Adults are black with yellow abdomen, less than 1 mm (1/20 inch) long (they do not sting). Larval stages live entirely inside immature whiteflies, which darken and turn black as the parasites develop inside.

Use as Biological Control:
Encarsia are used to control greenhouse whitefly on greenhouse cucumbers, tomatoes, peppers and poinsettias and other plants grown in greenhouses. They control silverleaf/sweet potato whitefly using high release rates. Optimum conditions are temperatures over 20°C (68°F) and relative humidity 50-70%. When daytime temperatures are less than 18°C (64°F). Encarsia activity is sharply reduced, making them less effective. Encarsia should not be used if high whitefly populations are already established.

The predatory beetle Delphastus avoids feeding on whiteflies parasitized by Encarsia, therefore it can be used with Encarsia. The parasitic wasp Eretmocerus californicus may also be used with Encarsia.

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 whitish.

Life Cycle:
The complete life cycle takes about 28 days at 21°C (70°F). Temperature affects developmental rate; for example, larval development takes 15 days at 25°C (77°F) and 45 days at 15°C (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 whitefly. Most Encarsia are female and each lays up 10 eggs per day for an average of 200 eggs. Larvae develop inside the whitefly scale for 10 days (at 20° - 25°C). 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 kill whitefly scales by feeding on the host directly; they also feed on whitefly honeydew.

Product Information:
Encarsia pupae are sold glued onto cards. It is important to hang the cards from lower leaves in the shade as Encarsia tend to fly upward; avoid wetting them while watering. If there are hanging baskets some cards must be placed on the baskets, as well as on infected plants.

If necessary, the Encarsia pupae can be held for up to 2 weeks at 5°-10°C (40°-50°F), however the percentage of emergence will decrease with time.

Introduction Rates:
1-10 Encarsia/m� (10 ft�) or 1-5 Encarsia/infested plant, every 1-2 weeks, until 80% of whitefly scales are parasitized. Encarsia are usually released in low numbers before pests are present (called an inoculative release), or, in higher numbers after pest populations are established (called an inundative release).

Above rates must be at least doubled for control of silverleaf/sweet potato whitefly or if temperatures are 18°C or less.

Encarsia tend to remain in regions where the whitefly are concentrated, therefore it is important to distribute them well:

For inoculative releases - spread introductions over 40 or more release points per 1,000 m �.
For inundative releases - use 60 or more release points per 1,000 m � and place more where whiteflies are found.

Once the percentage of parasitized scales exceeds 80%, the number of Encarsia present should be enough to control whitefly.

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 plant sources, such as weeds or previous crops, and from cuttings before Encarsia releases begin.

High whitefly populations hinder movement of the parasite as does the presence of excessive amount of honeydew. Remove whiteflies and honeydew by spraying with water or 1% Safer's® insecticidal soap.

When de-leafing plants, do not remove leaves that have significant numbers of black (parasitized) whitefly scales. If leaves must be pruned from plants, retain them, under the plants, until the wasps have emerged (1 to 2 weeks).

Using Pesticides:
Encarsia are extremely sensitive to insecticide residues. Plastic covering or flooring used in greenhouses may harbor residues at levels that are harmful to this parasite for over 6 months.
Spreader stickers in spray applications are harmful to Encarsia.

If whitefly hot spots develop, spot spray with Safer's soap (1% solution), weekly, directing the spray onto new leaves to kill adult whiteflies and early stages of scale. Kinoprene (Enstar®) may also be used on ornamental crops.