Description. The adult pink bollworm varies in size but is rarely over 3/8 inch in length. It is mottled grey in color with oval shaped wings. The wings are strongly fringed at the edges. The forewing is pointed at the tip. When at rest, the moth’s wings are folded close to the body. Under magnification, palpi can be seen emerging from the lower front part of the head. In contrast to most other moths, the palpi of pink bollworm are relatively thick, curved upwards and have light and dark colored bands. Also, the pink bollworm moths have a few stout hairs which project forward from the base of the antenna. Pink bollworm moths will typically live 4 to 8 days.
Pink bollworm eggs are rarely seen. They are small and yellow in color.
Eggs are usually laid singly inside the bracts of squares and under the calyx of bolls. Eggs normally hatch in 4 to 5 days.
The larvae are white but turn pink as they age. At hatching, the larvae have a dark head, but as they mature, the head becomes yellowish-brown in color. They enter squares or bolls very soon after hatching from the eggs. As they feed in squares or bolls they grow to a length of about ¾ inch. Larvae will feed for 10 to 14 days before pupating. Larvae usually will leave the the fruit and pupate in the soil, requiring about 8 days to transform into an adult.
Damage. Soon after emergence, pink bollworm moths mate and if cotton fruiting forms are available, the females begin
laying eggs on them. Some overwintering adults will emerge before there is squaring cotton available. This emergence is termed “suicidal” since the eggs are laid on vegetative tissue and the larvae do not survive. Pink bollworm larvae enter cotton fruit less than one hour after they hatch from the egg. Squares need to be 7 to 10 days old before they can support the growth and development of a pink bollworm larvae. The larvae feed and mature in cotton fruit. The first generation in the early summer feeds in squares, primarily on the anthers. Early in the season, infested squares continue growing and producing blooms. These infested blooms may have the petals tied together with silken threads, commonly termed “rosetted.” The rosetted flowers do not open normally, but will usually develop into a normal boll. This feeding normally causes loss of about 50% of the affected squares. Since first generation populations are almost always relatively low, little economic damage results from the feeding of first generation larvae in squares.
The eggs of later generations are laid on bolls. Larvae hatching from these eggs quickly enter the boll. They cause damage to the seed and lint. Additionally, boll-rotting organisms will often infect bolls through pink bollworm exit holes. In fields in which less than 50% of bolls become infested with a single larvae per boll, lint yield and quality losses are normally minimal because bolls mature, open and can be harvested. However, uncontrolled late season populations can reach very high levels with multiple larvae infesting single bolls. In these heavily infested fields bolls do not open and losses can be very high. Pink bollworm damage to bolls is evident on seed as stained lint. They will often leave entrance warts and mines on the inside carpal wall. Additionally, pink bollworm larvae do not hollow out the boll and leave frass on the outside of the boll as is often with a bollworm.
The bolls of upland cotton are most susceptible to pink bollworm from 14 to 21 days post bloom, while Pima bolls are most susceptible from 12 to 30 days post bloom. Once a boll is “rock hard” in firmness, it is generally immune to infestation to newly hatched larvae.
Management and decision making.
Cultural management. Strong cultural management systems provide the first line of defense against pink bollworm damage. Early, thorough stalk destruction is the foundation from which pink bollworm management systems in most areas of Texas are built. Texas Department of Agriculture operates a stalk destruction program in the southern, eastern and far western parts of the state. Research has shown that when a cotton producing area maintains seven or more months each year free of fruiting cotton plants, pink bollworm damage generally declines to the point that it is of minor economic significance. Since a part of the overwintering pink bollworm population spends the winter in bolls on plants and part overwinters in the soil (the majority of the population in Texas overwinters in the soil), both shredding and plowing of cotton stalks are important cultural management practices to reduce overwintering pink bollworm populations. Winter irrigation of the previous season’s cotton fields is also a very effective cultural practice to reduce overwintering pink bollworms, and rotating to small grains, an alternative summer crop, or leaving the ground fallow over the summer will greatly reduce pink bollworm populations in a given field.
The most effective means of managing pink bollworm in season is to plant cotton containing genes from the bacteria, Bacillus thuringiensis (Bt). These genes produce proteins that are toxic to most leaf and fruit feeding caterpillars after ingestion. Bollgard® cotton varieties were introduced in 1996 and contain only one gene (Cry 1Ac) for fruit and leaf feeding caterpillar control. Since then varieties containing multiple genes to control these caterpillars are now available and predominate Texas cotton acreage. Bollgard® II contains two genes (Cry 1Ac and Cry 2Ab) and Wide Strike® also contains two genes (Cry 1Ac and Cry 1F). Bt cotton is very effective against the pink bollworm and it has been a key component of pink bollworm eradication programs.
Since most pink bollworm damage occurs late in the season, planting fast maturing varieties can help prevent late-season pink bollworm damage.
Biological control. Predators and parasites have not contributed strongly to pink bollworm control in Texas or other infested areas of the southwestern United States. However, other components which fit under the broad definition of biological control have been very important in pink bollworm control and eradication programs.
Female pink bollworm moths produce and release into the air a sex pheromone which is highly attractive to male pink bollworm moths. Male moths respond to the pheromone. They fly in the airborne pheromone plume in the direction of the increasing concentration of the pheromone. When the pheromone concentration reaches a high level they land and begin a search for the female until they find her. Mating then occurs and fertile eggs can be laid. Scientists have successfully produced synthetic pink bollworm sex pheromone in the laboratory. When slow release systems containing pink bollworm sex pheromone are spread throughout pink bollworm infested cotton fields, the ability of males to find females and mate is greatly impaired. Unmated females do not contribute to pink bollworm population growth. Even delays in mating slow the rate of pink bollworm population development.
Sterile Insect Technology (SIT) is another form of highly effective, non-traditional biological control that is being used in Texas and other southwestern states to eradicate and control pink bollworm. Pink bollworms are mass reared in a USDA APHIS laboratory in Phoenix, AZ. The larvae pick up a red dye which has been added to the diet mixture so that lab reared moths can be distinguished from wild moths. Lab reared moths are sterilized with radiation and quickly shipped in internally cooled shipper/release boxes to cotton producing locations where they are released by special equipped aircraft over targeted fields. Sterile moths compete for mating with wild males and females. No viable larvae are produced by matings of sterile males with wild female moths.
Scouting. Pheromone traps are a very effective tool for pink bollworm population monitoring and they are the primary means of detection used by pink bollworm eradication programs. In eradication programs, pheromone traps effectively detect even very low level pink bollworm infestations. Pheromone traps are used to detect pink bollworm populations outside of eradication programs as well. The information they provide is useful in making treatment decisions (insecticide or mating disruption). Pheromone traps are best used in areas in which pink bollworm has caused significant crop damage in recent years and in fields not planted to Bt cotton varieties. Pheromone traps should be placed in fields at seedling emergence and monitored weekly until 4- to 5-leaf stage, then daily until 1/3-grown square stage.
Once the cotton has begun to bloom, trap captures averaging 5 or more moths per night should trigger field inspections for pink bollworm larvae. Bloom inspection at early bloom stage is a quick and effective way to estimate the pink bollworm population present in a field. Pink bollworm larvae which entered squares at early square stage can be easily found as large larvae in blooms when fields reach early bloom stage. Detection of pink bollworm larvae in rosetted blooms at levels above 1 to 2% is cause for concern and should be followed by regular weekly boll sampling for the remainder of the season. Rosetted bloom counts have not been the basis for treatment triggers in most production systems. Grower treatments to control pink bollworm (not eradication treatments) are rarely recommended or of significant value on early bloom stage cotton.
Grower treatment decisions on boll stage cotton are best made using percent boll infestation data. This data is obtained by collecting and inspecting bolls taken from fields. Boll sampling should be conducted primarily on non-Bt fields (due to the effectiveness of the Bt toxin against pink bollworms). Ten bolls should be pulled from each quadrant of the field, producing a sample of 40 bolls which will represent the field. The bolls should be cut with a knife or broken open. The inner carpel walls should be inspected for signs of pink bollworm entry. The larvae leave small warts or visible tracks on the inner carpel walls where they entered the boll. When these signs of boll entry have been found, the lint and seed near the entry damage should be inspected for the larva. Small larvae are tiny and white in color with a dark brown to black head. Older larvae are much easier to find since they are much larger and leave dark stains and droppings in the lint and on the seed. Fully grown larvae begin to develop the pink color. A small round hole through the carpel wall may be seen on older bolls. This is the exit hole of the larvae. Mature larvae cut out of the boll and drop to the ground to pupate. Boll samples should be collected and inspected each week from early boll set to open boll. When pink bollworms are evident, it is wise to inspect these fields twice weekly since larvae inside fruiting structures are impossible to effectively control.
Another tool that is available to aid in pink bollworm management and decision making is the heat unit model http://www.ipm.ucdavis.edu/calludt.cgi/DDMODEL?MODEL=PBW. The model predicts moth emergence and population peaks. It can be useful in knowing when to intensify sampling or time treatments for greatest effectiveness against adult moths.
Chemical control and Action thresholds.
Pink bollworm eradication. The El Paso/Trans Pecos zone and cotton production areas to the west of it in New Mexico, Arizona and California are conducting pink bollworm eradication programs. If any insects are found in these areas that are suspected of being pink bollworms, they should be reported to the local Texas Boll Weevil Eradication Foundation offices (Pecos or Tornillo, TX) or the state office (325) 672-2800.
Grower initiated control. Prior to first bloom, once pheromone traps exceed an average of 5 moths per pheromone trap per night, then a treatment is justified to prevent pink bollworm establishment. Treatment applications at pinhead sized square to 1/3-grown square stage may be insecticidal, pheromone mating disruptors, or a combination of these.
During the first 6 weeks of boll set, insecticide or mating disruption treatments are warranted when 10 to 15 percent of upland or 5 to 10 percent of Pima bolls are infested. Upland bolls should be protected until the last bolls to be harvested are 30 days old (30 days post-bloom) and rock hard. In Pima, bolls should be protected until 70 percent of bolls on the plants are open. In grower initiated control programs, insecticide treatments are normally more effective than mating disruption treatments against pink bollworm late in the season.
Since pink bollworm eggs are laid in concealed places and the larvae quickly bore into the square or boll, insecticide applications primarily target the moth. Pheromone traps and/or the heat unit model can be used to time treatments to the emerging moth flight. If large late season pink bollworm populations are present, damage prevention requires close interval treatments since only 2 to 3 days pass between adult emergence and the beginning of egg laying. Pink bollworm moths are generally most active between midnight and 3 AM, thus late afternoon or evening insecticide applications tend to be more effective than those applied in the morning.
|Suggested Insecticides and Rates for Managing Pink Bollworms in Cotton
ingredient per acre
|Amount of formulated
|Acres treated per gal or lb of
|Mode of Action Group (IRAC)|
|Cry 1Ac, Cry1F
(Baythroid XL 1)
|0.013-0.02||1.6-2.6 fl oz||80-49.2||3A|
(Lorsban 4E, generics)
(Asana XL 0.66E)
|0.03-0.05||5.8-9.6 fl oz||22-13.3||3A|
(Declare 1.25, generics)
|0.01-0.015||1.02-1.54 fl oz||125.5-83.1||3A|
(Karate 1 EC, generics)
(Mustang Max 0.8 E)
|0.018-0.025||2.8-4 fl oz||45.7-32||3A|
(Hero 1.24 EC)
|—||10.3 fl oz||12.4||3A|
1rates vary depending on product and formulation.