Walnut husk fly

Rhagoletis completa

The walnut husk fly is about the size of a housefly and very colorful. It has a yellow spot just below the areas where the wings are attached and iridescent, greenish eyes. The wings have three prominent dark bands, one of which extends around the wing to form a V-shape. The banded wings distinguish it from other flies found in the walnut orchard. Larvae feed in groups within the husk, but you won’t see them unless you remove the skin of the damaged husk. Dark, soft blotches on maturing husks are a good clue to husk fly presence. Blotches that are hard and dry are caused by blight disease and should not be confused with husk fly damage. This fly has one generation per year. Walnut husk flies overwinter as pupae in the soil and emerge as adults in some areas as early as May but generally around July 1. Peak emergence often occurs mid-July through mid-August. The female fly deposits eggs in groups of about 15 below the surface of the husk. Usually the first sign of an infestation is a small, stinglike mark on the husk caused by this depositing of eggs. At first these areas are difficult to see, but they soon darken and appear as little, black spots on the husk, usually near the stem end of the husk and often on the shaded side of the nut. Eggs hatch into white maggots within 5 days. The maggots feed inside the husk, enlarging the black area, which remains soft, unsunken, and smooth. The outer skin of the husk usually remains intact, but its fleshy parts decay and stain the nutshell. Older maggots are about 1/4 inch long and are yellow with black mouthparts. After feeding on the husk for 3 to 5 weeks, mature maggots drop to the ground and burrow several inches into the soil to pupate. Most emerge as adults the following summer, but some remain in the soil for 2 or more years.

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