CORN SILK FLY: Euxesta stigmatias, Otitidae

ADULT: These flies have a dark green body with normal length legs, and red to brown eyes. Their wings are patterned with four dark horizontal bands. Adults are active runners on plants often performing elaborate interactions involving wing flapping and running at and around other corn silk flies.

EGG: Thin, 1/16 in. long white eggs are deposited in silk channels, between ends of husks and around armyworm and earworm entrance and exit holes in husk. Larvae emerge in 2 to 4 d.

LARVA: White to pale yellow, legless maggots are narrow, reaching 3/8 to 7/16 in. long, with black mouth hooks. Larvae start feeding on silks often just inside tips of husks. They may continue to feed on silks advancing toward the tips of the ears, or they may feed extensively on kernels at the tips of the ear, or may disperse randomly throughout the ear to feed on kernels. Larvae complete development in 15 to 21 d. Exposed larvae quickly seek shelter by crawling or flicking themselves from the ears by grabbing and quickly releasing the end of their abdomen with their mouthhooks .

PUPA: The majority pupate within the soil and are rarely found within the ear. Maggots do not molt out of their last cuticle, but complete metamorphosis within it. The resulting delicate puparium is light to medium brown. Adults emerge in 7 to 8 d.

GENERATION TIME: 24 to 32 d.

DAMAGE: The geographic range of this insect has spread up the Florida peninsula during the last eight yr. from the Homestead region. This fly is a year round pest of corn in southernmost Florida. Corn grown just south of Lake Okeechobee is attacked primarily in the late Winter and Spring.  Corn in central Florida is attacked in late Spring and early Summer.  North Florida corn is prone to attack during the summer. This insect is saprophytic and feeds and reproduces on a wide variety of over-ripe and rotting fruits, vegetables and sugarcane. Females will deposit eggs into sweet corn ears for at least 3 wk after silk initiation, but seem to prefer ears with fresh silk. This pest damages ears in several ways. By damaging silks, the larvae disrupt pollination and reduce kernel density. Larval feeding at ear tips can force growers to have tips cut off at harvest. However, near-mature larvae are just as likely to damage individual kernels distributed throughout ears rendering them completely unmarketable. In south Florida, and other areas with appropriate local food reservoirs, these flies are quick to reenter treated fields. Therefore, damage along field margins and across fields with large field edge to acreage ratios can be substantial.

CONTROL: On corn, adults are usually found on the tassels and upper leaves early in the morning and late in the afternoon. This is the best time to scout them and to control them with chemicals. They move down the plants or at least into shaded parts of the plants during the day. Ovipositing females are most often observed on ears below the overhanging silks. Formulations, rates, and pre-harvest intervals of insecticides labeled for corn silk fly control in Florida are listed below for sweet corn (Table 1) and field corn (Table 2).

Table 1.  Chemical control of corn silk flies in sweet corn
Insecticide, formulation Rate/acre Min. days to harvest Application notes
cyhalothrin (Karate, Warrior) 1 EC 3.84 fl oz 1 suppression
ethyl parathion (Parathion) 8 EC 0.25 pt 12  
methyl parathion (Penncap-M) 2 EC 2 - 4 pt 3 ears; 12 forage, grazing  

Table 2.  Chemical control of corn silk flies in field corn
Insecticide, formulation Rate/acre Min. days to harvest Application notes
methyl parathion (Penncap - M) 2EC 2 - 4 pt 12