Preferred name: Anthonomus grandis
Authority: Boheman
Taxonomic position: Animalia: Arthropoda: Hexapoda: Insecta: Coleoptera: Curculionidae: Curculioninae
Common names in English: Mexican cotton boll weevil, boll weevil, cotton boll weevil, thurberia weevil
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Notes on taxonomy and nomenclature EPPO Categorization: A1 list
EU Categorization: A1 Quarantine pest (Annex II A)
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EPPO Code: ANTHGR

The principal host of A. grandis grandis is cotton, including Gossypium barbadense, G. hirsutum and wild Gossypium spp. (Gossypium arboreum and Gossypium herbaceum). Marginal reproduction has also been observed on the ornamental Hibiscus syriacus (Parrott et al., 1966). Feeding and foraging on pollen have been reported on a number of different hosts from a number of plant families (Hardee et al., 1999; Jones and Coppedge, 1999).

In the EPPO region, cotton is the only host to be considered. Wild Malvaceae might be attacked and act as reservoirs.

Host list: Abutilon, Cienfuegosia drummondii, Cienfuegosia rosei, Gossypium arboreum, Gossypium aridum, Gossypium barbadense, Gossypium davidsonii, Gossypium harknessii, Gossypium herbaceum, Gossypium hirsutum, Gossypium laxum, Gossypium lobatum, Gossypium sp., Gossypium thurberi, Gossypium turneri, Hampea nutricia, Hampea rovirosae, Hibiscus syriacus

Anthonomus grandis grandis is present across cotton growing areas in the Americas (South, Central, and North). From Mexico, the species spread into the United States of America in 1892, with the first report in the Lower Rio Grande Valley, Texas (Brazzel et al., 1996). It has since spread throughout the cotton growing area in the USA before the initiation of an eradication programme in the 1970s (Perkins, 1980; Raszick, 2021). Due to the success of the eradication programme, A. grandis grandis has been eradicated from 98% of the cotton growing region in the USA (USDA, 2022).

The weevil is present throughout Central America. In South America, A. grandis grandis has been reported in Venezuela (1949), Colombia (1951) (Scataglini et al., 2000), Brazil (1983) (Barbosa et al., 1983), Paraguay (1991), Argentina (1984), and Bolivia (1999) (Stadler and Buteler, 2007).

North America: Mexico, United States of America (Texas)
Central America and Caribbean: Belize, Costa Rica, Cuba, Dominican Republic, El Salvador, Guatemala, Haiti, Honduras, Martinique, Nicaragua, St Kitts-Nevis
South America: Argentina, Bolivia, Brazil (Alagoas, Bahia, Ceara, Distrito Federal, Goias, Maranhao, Mato Grosso, Mato Grosso do Sul, Minas Gerais, Paraiba, Parana, Pernambuco, Piaui, Rio Grande do Norte, Sao Paulo), Colombia, Paraguay, Venezuela

The post-embryonic development of the boll weevil undergoes three larval instars, the pupal stage, the pre-emergent adult stage, and finally, the adult stage. When feeding on large flower buds, developmental times for larva, pupa, and pre-emergent adult stages last, on average, 7.7, 2.0, and 4.2 days, respectively, at 25°C (Greenberg et al., 2005a).

Females start laying eggs after reaching reproduction maturation (≈3-4 days old). Females puncture the cotton fruiting structures to lay their eggs, usually one egg per structure. However, there can be more than one egg per structure, especially in late developing bolls (Neves et al., 2013). Oviposition punctures form small protrusions and differ from feeding punctures, which are small, uncapped holes. Despite the plasticity in laying eggs on flower buds, flowers, and bolls, females prefer to lay eggs on larger flower buds (5.5 to 8.0 mm) (Showler, 2005). One female can lay seven to 11 eggs per day for up to 21 days (Lloyd, 1986), depending on the female age, availability of flower buds, and environmental conditions. Egg incubation lasts, on average, 2.1 days at 25°C (Greenberg et al., 2005a), with the larvae showing developed head capsules and appendices seen through the chorion near the hatching time.

After completing development, the larvae moults and becomes a pupa inside a cell located inside infested buds and bolls. This structure will protect the adults formed, until they emerge from this structure (which may fall to the ground or remain on the plant).

A. grandis grandis can migrate long distances and it can disperse short distances.  It  hibernates in forest litter or on various malvaceous hosts, including regrowth cotton in warmer areas. 

There is high mortality rate in weevil populations interseason. About 95% of the hibernating adults die. Furthermore, heat, dry weather, natural enemies, and birds help materially to check rapid multiplication. Without such natural interference, the offspring of a single pair of boll weevils could amount to several million in one season. Under favourable conditions, the life cycle of A. grandis grandis is completed in 17-21 days, and as many as seven generations may develop in a year in the extreme southern part of the Cotton Belt in the USA.

Symptoms

Although adult weevils can feed on leaves and petioles, they only lay eggs on reproductive structures (Showler, 2007). Therefore, adults are commonly found in the flower buds and bolls protected by the bracts and in the centre of open flowers during warmer hours and are rarely seen on other parts of the plants. Because adults are not easily seen in the field, in the absence of the insect, the occurrence is assessed through damaged reproductive structures (buds, flowers, and bolls). As adults prefer flower buds over bolls for feeding and oviposition, they are most often seen in flower buds, especially the large (5.5-8.0 mm diameter) as well as the medium (3.0-5.4 mm diameter) sizes. Feeding and oviposition cause punctures at the base of flower buds, flowers, and bolls.

The bracteoles of oviposited flower buds spread out and turn yellow, and five to nine days after infestation, they turn brown and fall off (Silva et al., 2015; Showler and Cantú, 2005).

Oviposited small bolls (up to one week after anthesis) also fall off. Older infested bolls, containing larvae and pupae, remain on the plants and open irregularly or do not open. Signs of adults feeding on plants terminal shoots and young leaves can be seen before the flowering stage. After moulting into adults, weevils leave fallen or retained structures through exits hole.

Morphology

Egg

Eggs are slightly elliptical, opaque 1 mm long (Leigh et al., 1996).

Larva

A. grandis grandis larvae are C-shaped, legless, white to cream-colored, have a brown head, and strong mandibles. They can grow up to 13 mm long when fully developed.

Pupa

The pupae are 6-8 mm long, white to cream-colored, and resemble adults with visible legs, eyes, and mouthparts. According to Anderson (1968), female pupae can be distinguished from male pupae by the presence of a pair of lobes present near the anal opening in females, which are absent in males.

Adult

The adult is 5 to 8 mm long, with body weight varying as a function of food availability during the larval stage, reaching up to 20 mg (Greenberg et al., 2005b). Larger adults, up to 24 mg, occur when larvae develop on bolls than on flower buds. The adult has a long, slender rostrum bearing the pair of antennae geniculate (=elbowed) nearer the tip than the base. The mouthparts are at the end of the rostrum. Two larger and one smaller spine are easily seen on the inner side of the femur of the front legs.. Eyes are large, convex, and sloping dorsally, in front at the base of the rostrum. Adults vary from brownish-red when recently molted to the adult stage to near black with aging. The pronotum and elytra are covered by dense, whitish pubescence. The male rostrum is less smooth than that of females and has more pits, pores, and scales. The female rostrum is usually larger and flatter than the male’s (Soto and Reyes, 2014).

The posterior edge of the last tergite of the male (8th tergite), is notched in males and not in females (comparative pictures available at Agee, 1964; Sappington and Spurgeon 2000).

Detection and inspection methods

Visual examination of cotton plants is used to survey for A. grandis grandis but it can be difficult in large cotton fields, plants with dense foliage, and dense fruiting structures. In addition to the cryptic development the weevils as described above, adult boll weevils exhibit thanatosis (death feigning) when disturbed. At high levels of infestation, adults can be seen on the upper parts of the plants during the warmer hours of the day.

Anthonomus grandis grandis can be detected by using traps containing sex-and-aggregation pheromones. Traps containing rubber septum impregnated with pheromone are widely used to catch weevils when dispersing. Different tools have been tested, combining pheromones as an attractant and glue to hold the attracted weevils, or pheromone and the surface treated with an insecticide.

Despite the high efficacy of these tools in attracting and capturing weevils in certain circumstances, the efficacy of traps can be reduced due to the competition with the abundance of host and food availability and females inside the field. Kairomones have been incorporated in the mix with the aggregation pheromones to attempt to increase effectiveness (Magalhães et al., 2016).

Nucleotide sequences from a segment of the mitochondrial cytochrome C oxidase subunit I (COI) gene can be used to separate A. grandis grandis from A. grandis thurberiae (Barr et al., 2013; Alvarado et al., 2017).

In international trade, boll weevils may be carried with cotton seeds or bolls, with raw cotton and various cotton products (EFSA, 2017). Additionally, ornamental Malvaceae plants for planting (e.g. Hibiscus spp.) may be a pathway for movement though it should be noted that only marginal reproduction is shown (Parrott et al., 1966).

Natural dispersal can occur through flight and walking. The dispersal of adults right after emergence from fallen buds is predominantly achieved by walking to reach the base of nearby plants. In arid areas, thermal convection may disperse flying adult weevils over long distances. In central Texas, the greatest dispersal occurs from mid-August to September.

Economic impact

Boll weevil has been one of the most important pests on cotton in the USA (Schwartz, 1983; Williams, 1997). Since its entry into Texas (USA) in the 1890s, A. grandis grandis destroyed and reduced the quality of several billion USD worth of cotton, in an area of over 3 million ha. In the 1970s, USA cotton producers lost 200 million USD or more annually with suppression costing an additional 75 million USD annually; in fact, nearly one third of all pesticides applied to crops in the USA in the 1970s were used to control this pest.

Nowadays, A. grandis grandis is largely under control in the USA, though the pest still causes significant economic damage to cotton in South America (Burbano-Figueroa et al., 2021).

Control

Suppressing A. grandis grandis populations requires the adoption of different control tactics of Integrated Pest Management in the cotton crops. Their efficacy and use depend on the production system adopted from low- to high-input conventional cropping systems. Preventive tactics can be applied field-by-field but these have more efficacy when applied regionally. These are cultural control practices aimed at avoiding pest infestation. Collecting and destroying fallen fruiting structures in small fields can reduce population growth (Neves et al., 2013). Furthermore, trap crops established by seeding a strip of cotton plants earlier on the border of the definitive fields can detect infestation so that the grower can take localized curative control, reducing the number of future generations. Other measures, such as the adoption of adequate row spacing (Paim et al., 2021) and suitable planting dates (Santos et al., 2023), good control of cotton volunteer plants reduce the overall pest populations that can cause outbreaks.

Other control measures could include:

- Biotechnological control: transgenic Bt-cotton has been tried but not successfully obtained up to date; likewise, the use of the sterile insect technique (SIT) has been developed; use of pheromones (e.g. the aggregation pheromone grand lure) for mass-trapping is the most applied tool to detect boll weevil populations at the beginning of cultivation (when the cotton plants do not have reproductive structures).
- Biological control: conservation biological control; inundative biological control with the entomopathogenic fungus Beauveria bassiana, mass release of the parasitoid Catolaccus grandis (Hymenoptera: Pteromalidae).
- Chemical control: use of different pesticides is the most common curative tactic (Torres et al., 2022), often timed according to captures in pheromone traps, and applied after reaching 3-5% flower bud infestation with up to five applications, spaced 5 days to kill all adults as they emerge.
- Use of less preferred cultivars.

Phytosanitary risk

A. grandis grandis is essentially a subtropical pest, so that the cotton-growing area at greatest risk in the EPPO region would be the Mediterranean zone. It is questionable whether the weevil could survive the low winter temperatures of the Central Asian cotton-growing areas. For many years, A. grandis was confined in the USA to the more humid regions of the south, where there were significant amounts of summer rainfall. It was assumed that the insect could not survive in the hot, arid regions of the south-west. In the early 1950s, however, it gradually moved westward into some of these formerly unoccupied areas, and this further confirms the risk to Mediterranean countries.

Appropriate measures may include that cotton growing countries in the EPPO region can source seed or bolls of cotton from an area free from the pest (Pest Free Area). Raw cotton from the same origin (including waste fabric, waste cotton, cotton seed cake, meal, and bags that have been used as a container for lint or any form of unmanufactured cotton) can be treated in such a way that the material will be free from the pest. See EPPO (2018) for fumigation of cotton and cotton products.

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Anderson DM (1968) Observations on the pupae of Anthonomus grandis grandis Boheman and A. grandis thurberiae Pierce (Coleoptera: Curculionidae). Annals of the Entomological Society of America 61, 125-129.

Alvarado A, Jones RW, Pedraza-Lara C, Villanueva OA & Pfeiler E (2017) Reassessment of the phylogeography and intraspecific relationships of western and eastern populations of the boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), in North America. Biological Journal of the Linnean Society 20, 1-17.

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Barr N, Ruiz-Arce R, Obregón O, de Leon R, Foster N, Reuter C, Boratynski T & Vacek D (2013) Molecular diagnosis of populational variants of Anthonomus grandis (Coleoptera: Curculionidae) in North America. Journal of Economic Entomology 106, 437–449.

Brazzel JR, Smith JW & Knipling EF (1996) Boll weevil eradication. In: King EG, Phillips JR, Coleman RJ (eds.) Cotton Insects and Mites: Characterization and Management. Memphis: The Cotton Foundation Publisher, pp. 625-654.

Burbano-Figueroa O, Sierra-Monroy A, Martinez LG, Borgemeister C & Luedeling E (2021) Management of the boll weevil (Coleoptera: Curculionidae) in the Colombian Caribbean: a conceptual model. Journal of Integrated Pest Management 12. https://doi.org/10.1093/jipm/pmab009

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EPPO (2018) PM 10/25 Fumigation of cotton and cotton products to control Anthonomus grandis. EPPO Bulletin 48, 536.

Greenberg SM, Sétamou M, Sappington TW, Liu TX, Coleman RJ & Armstrong JS (2005a) Temperature-dependent development and reproduction of the boll weevil (Coleoptera: Curculionidae). Insect Science 12, 449-459.

Greenberg SM, Spurgeon DW, Sappington TW & Sétamou M (2005b) Size-dependent feeding and reproduction by boll weevil (Coleoptera: Curculionidae). Journal of Economic Entomology 98, 749-756.

Jones GD & Coppedge JR (1999) Foraging resources of boll weevils (Coleoptera: Curculionidae). Journal of Economic Entomology 92, 860–869.

Leigh TF, Roach SH & Watson TF (1996) Biology and ecology of important insect and mite pests of cotton. In King EG, Phillips JR, Coleman RJ(eds.) Cotton Insects and Mites: Characterization and Management, No. 3. The Cotton Foundation Reference Book Series. Memphis, Tennessee, pp. 17-85.

Lloyd EP (1986) Ecologia do bicudo do algodoeiro. In: Barbosa S, Lukefahr MJ, Braga Sobrinho RO (eds) Bicudo do algodoeiro. Brasília, Embrapa, pp. 135-144.

Magalhães DM, Borges M, Laumann RA, Woodcock CM, Pickett JA, Birkett MA & Blassioli-Moraes MC (2016) Influence of two acyclic homoterpenes (tetranorterpenes) on the foraging behavior of Anthonomus grandis Boh.  Journal of Chemical Ecology 42, 305-313.

Neves RCS, Showler AT, Pinto ES, Bastos CS & Torres JB (2013) Reducing boll weevil populations by clipping terminal buds and removing abscised fruiting bodies. Entomology Experimental et Applicata 146, 276-285.

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Raszick TY (2021) Boll weevil eradication: a success story of science in the service of policy and industry. Annals of the Entomological Society of America 114, 702-708.

Raszick TJ, Dickens CM, Perkin LC, Tessnow AE, Suh C, Ruiz-Arce R, Boratynski TN, Falco MR, Johnston JS & Sword GA (2021) Population genomics and phylogeography of the boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), in the United States, northern Mexico, and Argentina. Evolutionary Applications 14, 1778-1793.

Roehrdanz R (2001) Genetic differentiation of Southeastern boll weevil and Thurberia weevil populations of Anthonomus grandis (Coleoptera: Curculionidae) using mitochondrial DNA. Annals of the Entomological Society of America 94, 928-935.

Santos PJ, Dias AM, Campos KL, Araújo ACA, Oliveira AAS, Suinaga FA, Torres JB & Bastos CS (2023) Planting date of cotton in the Brazilian Cerrado drives boll weevil (Coleoptera: Curculionidae) infestation. Insects 14, 599.

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This datasheet was extensively revised in 2024 by Cristina Schetino Bastos (Faculdade de Agronomia e Medicina Veterinária, Universidade de Brasília, Campus Darcy Ribeiro, Brasília, Distrito Federal, Brazil) and Jorge Braz Torres (Departamento de Agronomia - Entomologia, Universidade Federal Rural de Pernambuco, Recife, Pernambuco, Brazil). Their valuable contribution is gratefully acknowledged.

EPPO (2024) Anthonomus grandis. EPPO datasheets on pests recommended for regulation. https://gd.eppo.int (accessed 2024-04-27)

This datasheet was first published in the EPPO Bulletin in 1979 and revised in the two editions of 'Quarantine Pests for Europe' in 1992 and 1997, as well as in 2024. It is now maintained in an electronic format in the EPPO Global Database. The sections on 'Identity', ‘Hosts’, and 'Geographical distribution' are automatically updated from the database. For other sections, the date of last revision is indicated on the right.

CABI/EPPO (1992/1997) Quarantine Pests for Europe (1^st and 2^nd edition). CABI, Wallingford (GB).

EPPO (1979) EPPO Data Sheet on Quarantine Organisms no 34: Anthonomus grandis. EPPO Bulletin 9(2), 4 pp. https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1365-2338.1979.tb02460.x