Excerpted from The Vegetable and Small Fruit Gazette.
September, 2001
Volume 5, No. 9

Bug vs. Bug- Managing Two-Spotted Spider Mite with the Predatory Midge Feltiella acarisuga
Cathy Thomas, Integrated Pest Management Program
Pennsylvania Department of Agriculture

Two- spotted spider mite (Tetranycus urticae) populations can increase rapidly especially during hot, dry periods. Most of the difficulty in controlling this pest is initial detection. Since there is no winged stage, sticky traps are ineffective, hence, plant inspection is the only method to assess if mites are present. Damage is caused by larvae, nymphs and adults piercing the plant cells and sucking out the contents. The damaged cells appear as yellowish white spots (chlorophyll is destroyed) on the upper surface of the leaf. As populations increase, the whole leaf will eventually turn yellow. Crop losses may occur when about 30% of the leaf surface is damaged.
(See July 2001, August 2001 issue for more information on managing two-spotted spider mite)
The most commonly used biocontrol for two-spotted spider mite is the predatory mite, Phytoseiulus persimilis. A natural enemy that can be used with predatory mites is the predatory midge, Feltiella acarisuga. Feltiella is good at finding hot spots, so the two predators are complimentary. Feltiella can be an effective year-round predator and is particularly useful on hairy leaved plants (such as tomatoes) . This is a predator that you might see naturally in your greenhouses (and garden) if spider mites densities are high and you are not using pesticides.

Life Cycle

The adult is a delicate, pink-brown fly, only about 1 mm long, with long legs. They do not feed and only live 3-4 days after emerging from the cocoon. High humidity improves midge emergence. Optimal conditions for Feltiella are 68-81°F and relative humidity greater than 60%, although larvae can tolerate a wider range of conditions than the adult. Adults actively search for spider mite colonies. Each female lays an average of 30 shiny yellow eggs near high densities of mites, usually where webbing occurs. The tiny eggs hatch in 5-7 days. The brownish yellow midge larvae grow to about 2 mm long. Upon hatching they move to a spider mite, sink their mandibles in, and suck out the contents. They can consume over 300 mite eggs as they complete their development in about a week in the greenhouse. Under cooler conditions the larval stage may take up to a month to complete. They then spin fluffy white cocoons on the underside of leaves, usually along a leaf vein, in which to pupate. The pupal stage lasts approximately one week in the greenhouse, but longer under cooler conditions.

Application

ß Start early to control spider mite populations since spider mites reproduce quickly at high temperatures and low humidity.

ß Always use Feltiella acarisuga in conjunction with a predatory mite such as Phytoseiulus persimilis.

ß Feltiella larva feeds on eggs, nymphs and adults of two-spotted spider mites.

ß Monitor for predator activity by checking spider mite colonies for larval development and for shriveled mites that have been fed upon. Monitoring should be done once a week, consistently.

ß Concentrate predator introductions at spider mite hot spots as soon as possible after delivery.

ß Open the box containing predators in the greenhouse and place as close as possible to spider mite infestations. Let the box stand for at least one week until adults have emerged.

ß Consult your supplier for rates and introduction schedule.

Products

Feltiella acarisuga is shipped to the grower as pupae on leaves in units of 250.

Product names from major suppliers of Feltiella acarisuga

ß Biobest – Feltiella – system (Therodiplosis persicae - system), www.biobest.be
303-661-9546

ß Kopperts – Spidend, www.koppert.nl, 734-641-3763

This predator can be obtained through most biological control distributors.

Benefits

ß The adult midge is capable of flying and locating colonies of spider mites.

ß Applicable in crops where scouting is difficult (ie.ornamentals)

ß Can and should be introduced with predatory mites such as Phytoseiulus persimilis.

ß Active in cold and dark weather in spring and fall.

Provides long lasting protection with several introductions.

Please phone or email me if there are specific issues you would like me address in this column.

Cathy Thomas
Integrated Pest Management Program
Bureau of Plant Industry/Rm. 100
2301 N. Cameron Street
Harrisburg, PA 17110