Sunflower Production Field Guide - Your "Home Page"

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of the developing sunfl ower 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 7.5 inches (19 cm)
deep in the soil by August or early September. Some
larvae will pupate in the sunfl ower head. Only one
generation per year occurs in North Dakota.
Strauzia longipennis has one generation per year. This
insect overwinters as a larva in plant debris in the
soil. Pupation and adult emergence is completed in
early June. Females lay eggs in stem tissue of young
sunfl ower, and larvae feed in the pith tissue for much
of the growing season.
■ Figure 43. Adult - Sunfl ower seed
maggot Neotephritis fi nalis. (Extension
Entomology)
■ Figure 44. Pupae - Sunfl ower seed maggot
Neotephritis fi nalis. (Extension Entomology)
Unlike the other two species of sunfl ower maggots,
two complete generations per year of N. fi nalis occur
in North Dakota. Adults of N. fi nalis emerge during
the fi rst week of July. Egg deposition occurs on the corolla
of incompletely opened sunfl ower infl orescences.
The total larval period is 14 days. The fi rst generation
of N. fi nalis pupates in the head; the second generation
overwinters in the soil as pupae.
Damage: Damage by sunfl ower maggots has been
negligible.
The maggots of Gymnocarena diffusa feed on the
spongy receptacle tissue of the sunfl ower head and
feeding may cause partially deformed heads. Larvae
do not feed on developing seeds.
The magnitude of damage to sunfl ower seeds by N.
fi nalis larvae depends largely on the stage of larval
and seed development. Seed sterility occurs when
newly hatched larvae tunnel into the corolla of young
blooms. Observations indicate that a single larva feeding
on young fl owers will tunnel through 12 ovaries.
Mature larvae feeding on older sunfl ower heads will
destroy only one to three seeds.
While infestation levels of S. longipennis occasionally
have reached nearly 100 percent, damage from larval
feeding is usually light. Part of a commercial sunfl
ower fi eld next to a grassed waterway or other water
source sometimes supports a higher than usual infestation.
Under these conditions, high larval numbers of
eight to 10 per stalk may be found and stalk breakage
can occur. Stalk breakage of up to 30 percent of the
plants has been recorded.
Scouting Method: A scouting method has not been
developed for sunfl ower maggots because of the negligible
injury caused by these insects.
Economic Threshold: None established.
Management: Insecticide use has not been warranted
for control of sunfl ower maggots.