|Walnut husk fly|
Rhagoletis completa Cresson
-- Helmut Riedl
Walnut husk fly adult
Walnut husk fly eggs in walnut (Ken Gray Image Courtesy of Oregon State University)
Egg: The egg is elongate, slightly curved and about 1/25 inch (1 mm) long. A freshly laid egg is pearly white. Shortly before hatching, the mouth hooks of the young larva can be seen.
Larva: The newly hatched larva is maggot-like and white except for its dark mouth parts. The larva turns yellow as it matures. It is about 1/2 inch long (13 mm) when mature. If a maggot is found in peach, it is probably walnut husk fly or Drosophila.
Pupa: The pupa is straw colored with conspicuous dark brown anterior spiracles. It is the size and shape of a large grain of wheat.
Walnut husk fly larvae in walnut (Ken Gray Image Courtesy of Oregon State University)
Egg laying begins anywhere from 2 to 6 weeks after the first emergence and continues until fall. The period before egg laying is much more variable than that of cherry fruit fly or apple maggot. Eggs are laid in groups of about 15 in a small cache beneath the fruit skin. Peaches are attacked when they are almost mature. Eggs hatch within 5 days. The white maggots feed inside the fruit for 3 to 5 weeks, depending on the temperature.
Mature larvae leave the fruit through a small exit hole or the hole through which the eggs were deposited, usually at the opposite end of the fruit from the stem. They drop to the ground and burrow into the soil to pupate. They remain in their pupal case for at least a year. Some remain in diapause for 2 years and a few even 3 or 4 years.
Walnut husk fly damage to walnuts (R. Van Steenwyk)
Green sticky sphere for monitoring walnut husk fly (R. Van Steenwyk)
Yellow sticky trap for walnut husk fly (R. Van Steenwyk)
At the beginning of July, hang traps at least 6 feet above the ground in a shady part of the tree. If husk flies were a problem the previous year, hang traps in trees that were infested.
The husk fly has few natural enemies. A predatory mite, Pyemotes ventricosus, and an anthocorid bug, Triphleps insidiosus, have been seen feeding on eggs. Ants and spiders reportedly prey on larvae and adults. However, these predators have little impact on husk fly populations.
Bait droplets sprayed for control of walnut husk fly (R. Van Steenwyk)
Remove fallen infested fruit and remove the source of the infestation, probably a nearby walnut tree. Apply an insecticide recommended for walnut husk fly that is also registered on peaches within 10 days after trap catches show a sharp increase over a 3-day period. This will usually be from late July to mid-August. Apply again in 10 days if the husk fly was a problem the previous year. A third application may be needed 3 to 4 weeks later if flies continue to be caught in traps. A protein bait can be used to attract the flies to the insecticide to make it more effective.
Because some pupae remain in the ground for more than one year, flies may continue to appear after the source is removed and control may be needed over several years.