Cotton boll weevil

Anthonomus grandis Anthonomus grandis Boheman, 1843 · formerly or also: Mexican cotton boll weevil

picudo del algodonero · Spanish, Mexico and South America
bicudo-do-algodoeiro · Portuguese, Brazil
anthonome du cotonnier · French, French-speaking regions

The boll weevil is a small grey-brown weevil whose larvae develop inside cotton flower buds (squares) and young bolls, causing them to drop or rot. After entering Texas from Mexico in 1892 it spread across the US Cotton Belt and changed Southern agriculture. A coordinated eradication programme has since removed it from almost all US cotton and northern Mexico, but it remains the most serious cotton pest in Brazil and other parts of South America.

Adult boll weevil (Anthonomus grandis) on a cotton square, showing its long snout. Photo: Agricultural Research Service , United States Department of Agriculture ., Public domain, via Wikimedia Commons.

Type: Insect · Insect (weevil, a beetle with a long snout)
Classification: Animalia › Insecta › Coleoptera › Curculionidae
Main crops: Cotton
Found in: Mexico and Central America, United States, South America, Caribbean
Chemical groups: IRAC 1B, IRAC 3A (mode-of-action groups, not products)
Last reviewed: 2026-10-20

Cotton boll weevil scientific name, order and family

The scientific name of cotton boll weevil is Anthonomus grandis Anthonomus grandis Boheman, 1843, in the order Coleoptera, family Curculionidae.

Older or alternative scientific names: Mexican cotton boll weevil.

Where it occurs

Native to Mexico and Central America. It reached Texas in 1892 and the whole US Cotton Belt by about 1922; it was detected in Brazil in 1983 and is present in Paraguay, Argentina, Colombia and Venezuela. It has been eradicated from the US except for the Lower Rio Grande Valley of Texas, and from northern Mexico. It is a quarantine pest elsewhere.

Region	Status
Mexico and Central America	Native; eradicated from northern Mexico
United States	Eradicated except southern Texas
South America	Widespread; major pest in Brazil
Caribbean	Present on some islands

Symptoms and identification of cotton boll weevil

Boll weevil on a cotton boll. Photo: Clemson University - USDA Cooperative Extension Slide Series,, CC BY 3.0 US, via Wikimedia Commons.

The organism

Adults are about 4-8 mm long, grey to reddish-brown, with a long, slender snout about half the length of the body and two small spurs on the thigh of each front leg. Larvae are white, legless and C-shaped with a brown head, and live inside squares and bolls.

Signs in the crop, stage by stage

Crop stage	What you see
Squares (flower buds)	Small feeding and egg-laying punctures sealed with a wax-like plug; bracts flare open ('flared squares') and squares turn yellow and drop.
Young bolls	Punctures on bolls; larvae feed inside, destroying lint and seed; bolls rot or open poorly.
Field	Few squares retained on plants; adults on terminals and in squares, especially near field edges early in the season.

Life cycle of cotton boll weevil

Life cycle of Cotton boll weevil — diagram drawn by Laisha from the stages below. Durations depend on temperature.

Adults leave winter shelter in leaf litter and woodland edges and move into cotton when squares form. Females lay eggs singly in holes they chew in squares and young bolls. The larva feeds and pupates inside, and new adults emerge through a hole. As days shorten in autumn, adults enter diapause and move to overwintering sites.

Stage	Duration	Notes
Egg (inside square or boll)	About 3-5 days	One per puncture.
Larva (3 instars)	About 7-12 days	Feeds inside.
Pupa (inside square or boll)	About 3-5 days	Protected from sprays.
Adult	Several weeks in summer; months in diapause	Females lay 100-300 eggs.

Temperature

Egg to adult takes about two to three weeks in summer; development stops in cold weather, and winter survival is higher after mild winters.

Generations

Several generations per season; more in long seasons and continuous cotton areas.

Conditions that favour it

Long growing seasons, cotton stalks left standing after harvest, volunteer and regrowth cotton, nearby woodland and litter for overwintering, mild winters and staggered planting dates.

Economic threshold level (ETL)

There is no single international threshold. Programmes set action levels based on the percentage of squares with egg-laying punctures and on trap catches, which differ between countries and regions; in eradication zones any detection triggers action.

Thresholds are local. They depend on crop price, control cost, variety and natural-enemy activity, so use the figure your local extension service publishes where one exists.

Damage and yield loss from cotton boll weevil

Without control, the boll weevil can destroy most of a cotton crop. Its spread across the southern US in the early twentieth century caused large losses and changes in farming; today, in Brazil, it requires many insecticide applications per season and greatly raises production costs.

Monitoring

Use pheromone-baited traps around fields and overwintering sites to detect adults.
Inspect squares on a set number of plants weekly for egg-laying punctures, and collect fallen squares to check for larvae.
Check field borders next to woodland first, early in the squaring period.

How to control cotton boll weevil (integrated management)

Control works best as a sequence: prevent, monitor, then act only when a threshold or a risk forecast says so, using the least disruptive option that works.

Cultural control

Destroy cotton stalks immediately after harvest and enforce a cotton-free period, so that weevils have no food before winter.
Plant within a short, uniform window across an area and use earlier-maturing varieties to shorten the season.
Collect and destroy fallen squares and bolls in small fields; remove volunteer and regrowth cotton.

Mechanical and physical control

Pheromone-baited trap tubes treated with insecticide are used around fields in some programmes.

Biological control

Parasitic wasps, fire ants and other predators, and pathogens such as Beauveria bassiana kill larvae and adults, but rarely give enough control alone.

Host resistance

No resistant cotton varieties are available; Bt cotton does not control the boll weevil.

Chemical control of cotton boll weevil — by mode-of-action group only

Laisha names chemical options only by their resistance-committee mode-of-action group (IRAC for insects, mites and nematodes, FRAC for fungi, oomycetes and bacteria, HRAC for weeds), never by active ingredient or product. What is registered differs by country and changes over time; the label and your local plant-protection authority decide what may be used, on which crop, at what rate and with what pre-harvest interval.

Sprays target adults before and during early squaring, because eggs, larvae and pupae inside squares and bolls are protected. Area-wide eradication combines trapping, stalk destruction and timed sprays. What is registered differs by country and changes over time; follow the label and your local plant-protection authority.

Scheme	Group	Mode of action	Notes
IRAC	1B	Acetylcholinesterase inhibitors (organophosphates)	Used in eradication programmes; highly toxic.
IRAC	3A	Sodium channel modulators (pyrethroids)	Harmful to natural enemies; can cause secondary pest outbreaks.

Resistance management

Rely on area-wide stalk destruction, short planting windows and trapping to reduce spray numbers, and rotate groups.

Look-alikes and how to tell them apart

Pepper weevil (Anthonomus eugenii) — Similar weevil found in pepper, not cotton.
Cotton bollworm and other bollworms — Caterpillars with legs that make larger holes in bolls; no punctures sealed with plugs.
Square shedding from stress — Fallen squares without punctures or larvae, after drought, heat or cloudy weather.

Host range

Cotton (Gossypium species) is the only important host for reproduction; a few related wild Malvaceae (such as Hampea and Cienfuegosia species) also support it.

What is still uncertain

The future spread of the weevil in South America and the long-term success of eradication there are uncertain.
Thresholds and spray needs vary greatly with region and season length.

Grow guides for its host crops

How to grow the crop well is the first line of defence. Laisha's free grow guides cover each crop from sowing to harvest:

How to grow Cotton

Not sure this is what you are seeing?Ask Laisha: describe the symptoms or send a photo, and get a reasoned first read with what to check next — for your crop, your stage and your region.Ask Laisha

Sources

Anthonomus grandis (Mexican cotton boll weevil) datasheet — CABI Compendium. https://doi.org/10.1079/cabicompendium.5735
Anthonomus grandis (ANTHGR) — EPPO Global Database. https://gd.eppo.int/taxon/ANTHGR
Benefits of the boll weevil eradication program — USDA APHIS (via Biodiversity Heritage Library). https://doi.org/10.5962/bhl.title.102086
Boll weevil eradication — Science (AAAS). https://doi.org/10.1126/science.207.4435.1044

Written by Laisha from the sources above, in its own words. This page is general reference, not a prescription: confirm identification locally and follow the label and your plant-protection authority.