Sunflower Maggot Fly – Strauzia longipennis

Live adult female flies photographed at DuPage County, Illinois. Size: 8mm. Adults have a short lifespan. Sometimes call peacock flies after their showy colors and mating displays. This large fruit fly's larvae is commonly called called the Sunflower Maggot, after its habit of infesting both wild and cultivated plants of the sunflower family.

There are three species of sunflower maggots that are pests of cultivated sunflower and attack different parts of the plant. These include the sunflower receptacle maggot, Gymnocarena diffusa (Snow), the sunflower maggot, Strauzia longipennis (Wiedemann), and the sunflower seed maggot, Neotephritis finalis (Loew) (Diptera: Tephritidae). The adult forms of all three sunflower maggots have wings with a distinct brown or yellowish‑brown pattern. While all three fly species are similar in appearance, they do have distinguishing differences.

The sunflower receptacle maggot is the largest of the three with a body about 10 mm long and a wing span of approximately 19 mm. The eyes of this species are bright green and the wings have a yellowish‑brown and somewhat mottled appearance. The larvae are yellowish‑white in color attain a length of nearly 8 mm at maturity. The adult has a wing spread of about 13 mm and a body 6 mm long. The wings bear broad, dark bands that form a fairly distinct F‑shaped mark near the tips. The larvae of the sunflower maggot are creamy-white and attain a length of about 7 mm at maturity. The sunflower seed maggot is the smallest of the three species with a body length of the adult about 6 mm and a wing span of approximately 7 mm. The wings have a brown lace‑like appearance. The larvae attain a length of 4.5 mm at maturity. The small, brown pupae are found in the face of the sunflower bud, usually surrounded by a small number of damaged disk flowers.

Adults of the sunflower receptacle maggot emerge in late June to early July after sunflower buds reach 5 to 10 cm in diameter. Eggs are laid on the bracts of the developing sunflower heads. Egg laying occurs from mid-July through August. The hatched larvae tunnel into the spongy tissue of the receptacle. Damage to the head is negligible. After 30 days, the mature larvae cut a small emergence hole on the underside of the receptacle and drop into the soil to pupate. Overwintering pupae are found about 19 cm deep in the soil by August or early September. Some larvae will pupate in the sunflower head.

The sunflower maggot has one generation per year. This species overwinters as a larva in plant debris in the soil; pupation and adult emergence are completed in early June. Females lay eggs in stem tissue of young sunflower, and larvae feed in the stem pith tissue. Unlike the other two species of sunflower maggots, two complete generations per year of N. finalis occur in North Dakota. Adults of sunflower seed maggot emerge during the first week of July and oviposition occurs on the corolla of incompletely opened sunflower inflorescences. The total larval period is 14 days. The first generation pupates in the head; the second generation overwinters in the soil as pupae. Economic damage from any of these species is rare. The magnitude of damage to sunflower seeds by sunflower seed maggot larvae largely depends on the larval stage and seed development.

Seed sterility occurs when newly hatched larvae tunnel into the corolla of young blooms; a single larva feeding on young flowers will tunnel through 12 ovaries. Mature larvae feeding on older sunflower heads destroy only one to three seeds. While infestation levels of the sunflower maggot have occasionally reached nearly 100 percent, damage within sunflower stalks from larval feeding usually is light. (1)

Flies of North America – Order Diptera. Flies are prevalent in virtually all habitats, with over 16,000 species in North America. Flies can be distinguished from all other insects in that they only have one pair of normal wings. The other pair has evolved into small ball-like structures called halteres. Most flies have compound eyes and mouthparts adapted for piercing, lapping or sucking fluids.
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