Tobacco Budworm (Heliothis virescens)

Introduction
The tobacco budworm (TBW) is native to North America and can be found ranging as far north as Canada and as far south as Argentina. In the United States the TBW can be found in all cotton-producing states, and along with the cotton bollworm, has historically caused more damage to cotton than any other pest. The cotton bollworm feeds on a wider variety of plants and has a broader distribution than TBW. The TBW and cotton bollworm have similar life cycles, larval features and feeding damage. The TBW has a history of becoming more resistant to foliar insecticides than cotton bollworm. However, the introduction of Bacillus thuringiensis (Bt) cotton has provided highly effective plant protection against the TBW, resulting in reduced overall pest status for this insect in recent years.

Identification
The damaging larval stages of the TBW and cotton bollworm are smooth (relatively hairless) and difficult to tell apart without the aid of a microscope. Under a microscope, TBW can be distinguished from the bollworm by the presence of a raised area (mandibular tooth) on its jaw, and a single spine on the tubercle of the first, second and eighth abdominal segments. TBW larvae grow up to 1.5 inches in length and their color is quite variable, ranging from very dark to light green or pink. Adult moths have light brown wings with 3 to 4 light brown diagonal bands and wingspan of 28 to 35 mm. The eggs are spherical, with a flattened base. They measure up to 0.51 to 0.60 mm in diameter. Eggs initially are whitish to yellowish white in color, but turn gray as they age.

Biology
TBW overwinter as pupae in the soil with adult moths usually emerging in March when temperatures warm up. The TBW feeds exclusively on broadleaf plants (weeds and cultivated hosts) and may be found on alternative hosts other than cotton early in the season. Budworm populations generally do not reach large numbers until they move into cotton. Female moths will lay up to 1500 eggs over a 3 to 12 day period in cotton. The eggs are initially white in color and are frequently found on the upper 1/3 portion of the plant. Usually eggs are laid on smaller leaves or in terminals. If hot dry conditions exist however, moths may lay further down in the plant canopy. Eggs darken as they mature and hatch in 3 to 5 days depending on the temperature. Larvae normally double in size every day for the first four days. Larvae will feed for 16 to 17 days before pupating in the soil. A complete life cycle may take 27 to 35 days during the hot summer months, but will be longer during cooler months.

Multiple generations can occur. The number of generations depends on climate, with usually 3 to 4 generations in cotton.

Damage
TBW and cotton bollworm larval feeding result in very similar damage. Early instars will feed on leaf tissue often leaving pinhole damage. In the terminal, young larvae will feed on the squares, sometimes boring into the squares, resulting in the abortion or shedding of the damaged plant part. Older larvae will move down the plant and can feed on bolls before they are hardened. Boll damage, like square damage, may result in the abortion of the affected plant part.

Control
Transgenic Bt cotton (e.g., WideStrike^™ Insect Protection) provides excellent, season-long protection from TBW larvae. Bt cotton has reduced the concern for TBW in many cotton growing areas.

For non-Bt cotton (or Bt cotton with mixture of budworm and less susceptible pests), several classes of foliar insecticides are recommended, including Tracer^® insect control. Tracer provides effective control of TBW (including pyrethroid-resistant strains) while leaving most beneficial insects unharmed. To promote resistance management, rotation of insecticide chemical classes is strongly recommended. Foliar spray applications should be timed so that they coincide with egg hatch. Young larvae are often exposed on the plant terminal and easy to treat. Larvae deeper in the canopy may require additional applications with higher volumes of water. Treatment thresholds vary by state and time of year. Contact your local extension specialist to determine when treatment is warranted in your area.

Predators and parasites can also play an important role in reducing the population of TBW if insecticide treatments have not removed or severely reduced the population. Many common predators and parasites can be found attacking TBW including, big eyed bugs (Orius spp.), Apanteles marginiventris, Trichogramma spp. and Microplitis croceipes.