Insect Management
Cotton Insect Management
Boll Weevil -
Anthonomus grandis (Boheman)
Description
The small white eggs, which hatch into larvae, are deposited inside larger
squares. The square drops off the plant as a result of damage from larval
feeding. The larva is a small white grub about 1/4 inch in length when mature.
The larvae feed for 7 to 11 days and develops completely inside the square into
the pupal stage. The pupa is creamy white initially and resembles the adult, but
is inactive. As the pupae develop, they begin to show color changes - first
black eyes, then just before emergence as an adult they turn brown or tan
overall. The adult boll weevil emerges from the pupal stage. The newly emerged
adult boll weevil is a reddish - brown and the older overwintered weevil is
gray. Both are about 1/4 inch in length and have a beak or snout that is about
1/2 as long as the body length. Two large spines occur on the front pair of
legs.
Biology
The adult boll weevil overwinters near cotton fields in wooded areas, along
ditch banks, and around old houses or similar areas that have ground debris to
protect them. In the spring they return to the nearest cotton field. This
results in the first boll weevil damage normally being near overwintered areas.
The female weevil lays an average of 150 eggs. In the egg laying process, the
female weevil eats a hole in a square or small boll, lays a single egg inside,
and then seals it with a gum-like secretion. This secretion dries and appears as
a small yellowish bump or raised area on the square. The hatching eggs cause
squares to flare and drop to the ground in 5 to 7 days. The average time to
complete the life cycle from egg to emergence of adult is 21 days. In midsummer
the life cycle may be as short as 16 days.
Damage
The boll weevil adult causes damage to squares with buds 1 /4 inch or larger
in diameter and to small bolls by feeding and laying eggs inside them. The
damage done by adult feeding or the young developing larvae causes squares to
flare and drop. Normally, squares only fed upon will bloom unless feeding is
extensive and damages the internal structures - in which case, shedding will
occur. Damaged bolls drop or develop abnormally after egg lay or feeding damage.
Feeding signs may be recognized by a small hole in the square that turns dark
with time. The cotton scout can recognize boll weevil feeding by the yellow to
orange fecal material present on the square.
Scouting
Check for damaged squares during whole plant inspection at each sample site.
Scouts should pay particular attention to areas next to overwintered sites where
boll weevil damage occurs first. Damage continues throughout the season. Count
the number of weevil punctured squares found in all samples.
Treatment thresholds are based on the number of punctured squares per row
foot. Treatment thresholds are based on the number of punctured squares per row
foot.
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