Mimeo E-79
July, 1964
Purdue University
Cooperative Extension Service
Department of Entomology
DROSOPHILA FLY CONTROL
FOR TOMATO GROWERS AND PACKERS
Any tomato products found contaminated with Drosophila eggs, maggots or flies are subject to seizure under Federal law. Therefore, Drosophila (fruit fly) control is extremely important to both tomato growers and packers.
Infestations develop in cracked or damaged fruit in the field and in harvested fruit just before processing. Also, adult flies may drop into a tomato product during the processing operation.

CHARACTERISTICS OF THE FRUIT FLY
Several species of fruit flies complete development in tomato fields, but only Drosophila melanogaster becomes abundant enough to cause problems . This species does not overwinter outdoors in Indiana. Consequently, it moves into a growing area gradually each year and does not build up until just before harvest. The population then increases rapidly as more and more cracked or damaged fruits become available for egg laying.
A complete generation of Drosophila requires about 8 days. Adult flies live from 3 to 5 weeks and lay about 1,000 eggs. In the field, the flies congregate in lush, heavy growth, which provides the proper temperature, humidity and protection for continuous egg laying. Adult flies are also strong flyers and move easily from field to field.

DETERMINING FIELD INFESTATIONS
The "bait" method can be used as an aid to determining whether Drosophila infestations exist in a field and how serious they are. Here's how it works:
Ripe tomatoes are slit vertically on opposite sides about 1/8 inch deep and 1 1/2 inches long, and are squeezed gently to
open the cuts. They are then placed in shade under the vines, and each location is marked with a stake. About 10 "baits" will do for the average field. After 24 hours the fruits are examined for fly eggs with a low-power hand lens. The eggs are pearl-white and barely visible to the naked eye. Three to 5 eggs per slit signals the need for field spraying. Ten eggs per slit indicates that fruit should be dusted with pyrethrins after it is picked. A constant check should be kept on the build up of Drosophila populations since flies move in rapidly when feeding and egg laying conditions are favorable.

CONTROL MEASURES IN THE FIELD Cultural Practices
Three practices will help hold Drosophila infestation in check:
1. Use crack-resistant tomato varieties whenever possible.
2. Keep rows far enough apart to minimize fruit damage during cultivation, spraying and harvesting.
3. Keep roadways clean for spraying operations, stacking hampers and truck use during harvest.
Field Spraying
Field infestations are greatly reduced by spraying the crop a few days before and during harvest. The critical (and most effective) time is right at harvest when the fruit is ripe and easily bruised or crushed by pickers and trucking crews. However, if infestations are heavy before harvest, start field sprays then, and repeat at 4 to 6-day intervals as long as needed.
Suggested insecticides are in Table 1. Diazinon is preferred. Either liquids or granules can be applied with aerial or ground equipment, but granules give longer protection.