GLADIOLUS THRIPS

MARY F. BENSON

a , Adult thrips; b, egg; c, larva; d, pupa (or resting stage); e, foliage and flower spike showing typical feeding injury; /, uninjured gladi- olus corm; g, corms injured by feeding of thrips, showing charac¬ teristic russeted appearance, (a, b, c, and d about 20 times natural si^e; e, /, and g about one-half natural siz,e.)

(See other side for life history and control)

Bureau of Entomology and Plant Quarantine United States Department of Agriculture

Picture Sheet No. 6

GLADIOLUS THRIPS

( Taeniothrips simplex Mor.)

Life History

The gladiolus thrips overwinters on the stored corms, where feed¬ ing and reproduction are continuous as long as the temperature is above 50° F. During the growing season the foliage and flowers of the growing plant are attacked. The eggs are inserted in the plant tissue. Under favorable conditions a generation of the thrips may be completed in 2 weeks or less. The larvae and adults are responsible for the injury; no feeding occurs in the pupal stage.

Control

This thrips is subject to chemical control, either on the stored corms or on the growing plants. Very often both types of control measures may be used.

Control on the Corms

On dormant corms the thrips may be eliminated by the use of naphthalene flakes. Apply the flakes at the rate of 1 ounce per 100 corms and leave them with the corms for 4 weeks at a temperature of 60° to 70° F. The conns may be contained in paper sacks, or in bulb trays or boxes covered with paper. Do not use naphthalene on non- dormant corms. If late spring treatments are necessary, soak the conns for 12 to 24 hours in a solution of 1 ounce of mercuric chloride (corrosive sublimate) in 7){ gallons of water, in an earthenware or wooden container.

Control on the Plants

The growing plants should be watched for evidence of thrips feeding; and if such feeding is noted, spraying should be begun at once and continued at weekly intervals until flowering. If infested plants are not sprayed until blooming, the flowers cannot be saved. The spray should be applied as a fine mist, and an effort made to avoid run-off.

The recommended spray combination is as follows:

Small Large

quantities quantities

Tartar emetic _ 1 ounce. 2 pounds.

Brown sugar _ 2 ounces. 4 pounds.

Water _ 3 gallons. 100 gallons.

1 0—20760

April 1941

U. S. Government Printing Office

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