Insect Management
Cotton Insect Management
Cotton Bollworm -
Heliothis zea (Boddie) or
Tobacco Budworm -
Heliothis virescens (Fabricius)
Description
The cotton bollworm and tobacco budworm larvae appear the same externally,
but the adult stage is distinctly different. Some microscopic differences occur
in other stages of development. The developmental stages of both insects include
egg, larva, pupa, and adult. The small white egg is laid by the adult moth and
is about the size of a pin head. Eggs are usually found on plant terminals,
stems or top of leaves, but may be deposited any place on the cotton plant.
The larvae range in color from light greenish - yellow to reddish - brown.
Several dark stripes occur on top of the body. Length ranges from 1 / 32 to 1-1
/ 2 inches depending upon the stage of larval development. Five pair of prolegs
occurs at the rear of the body. The pupa is usually found 2 to 6 inches beneath
the soil surface. The adult bollworm moth varies in color from reddish - brown
to a whitish green-brown. A black or dark spot occurs in the center of the front
wing near the forward edge. The hind wing has a dark border along the rear outer
edge. The adult tobacco budworm moth has a brown to green color body. The wings
have three dark green and off-white bars occurring diagonally across the front
wing. The hind wing has a light brown appearance and the wing tips are a darker
brown that is edged with white.
Biology
Bollworms and budworms feed on a wide range of host plants including
lespedeza, Carolina geranium, tobacco, and cotton. However, tobacco budworms
rarely feed on corn, soybean, or grain sorghum which are hosts for the cotton
bollworm. The eggs are laid singly and hatch in 3 to 5 days into young larvae.
The larvae feed for about 16-17 days on young terminals, squares, and bolls. A
generation is completed in 27 to 35 days during the summer months. Many
predators and parasites prey upon the bollworm and contribute to its control
particularly during the early part of the growing season.
Damage
Bollworms only cause damage in the larval stage. Young larvae usually feed
first on terminals and small squares and may sometimes destroy the terminal bud.
This results in branching of the plant. The squares and bolls are fed upon
extensively by larvae and serious damage occurs in a relatively short period of
-time. Larvae feed on 6 to 7 squares and 2 to 3 bolls during their developmental
period. Bolls fed upon usually rot and don't develop further.
Scouting
The examination of cotton plants for bollworm and tobacco budworm larvae
involves looking for and counting the eggs, larvae, damaged squares, and bolls
at each sample site during the whole plant search. Treatment levels are based on
average numbers found per row feet. Many of the eggs and young larvae are found
in terminal areas of plants around the tender new growth, but the entire plant
should be examined for eggs and small larvae. Small larvae feeding on the
terminals cause the tender growth to appear brown and slightly ragged. Later in
the season, eggs are laid on squares and blooms lower in the plant. Larval
damage to squares and bolls is indicated by a feeding hole in the side of the
fruiting structure.
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