Anthonomus grandis (Mexican cotton boll weevil)
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- Risk of Introduction
- Hosts/Species Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Impact Summary
- Detection and Inspection
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Anthonomus grandis Boheman, 1843
Preferred Common Name
- Mexican cotton boll weevil
International Common Names
- English: boll weevil; cotton boll weevil; Thurberia weevil; weevil, boll; weevil, cotton boll; weevil, Thurberia
- Spanish: grillo de la capsula del algodonero; grillo de la cápsula del algodonero; picudo del algodón; picudo del algodonera
- French: anthonome du cotonnier; charançon américain del algodero; charançon du cotonnier
Local Common Names
- Germany: Kaefer, Mexikanischer Baumwollkapsel-
- Iran: susske ghusake panbeh
- Italy: antonomo del cotone
- Turkey: pamuk goz kurdu
- ANTHGR (Anthonomus grandis)
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Uniramia
- Class: Insecta
- Order: Coleoptera
- Family: Curculionidae
- Genus: Anthonomus
- Species: Anthonomus grandis
Notes on Taxonomy and NomenclatureTop of page A. grandis belongs to the Family Curculionidae subfamily Curculioninae, tribe Anthonomini (following the classification in Alonso-Zarazaga and Lyal (1999)), although some authors treat it as being in the subfamily Anthonominae.
The species is segregated on the basis of several adult characteristics into three subspecies: Anthonomas grandis grandis (south-eastern boll weevil); Anthonomas grandis thurberiae (Thurberia or Arizona wild cotton boll weevil); and an intermediate form known as the Mexican boll weevil. The subspecies A. grandis thurberiae was described from the host Thurberia thespesioides (also known as Gossypium thurberiae). Analysis of the mitochondrial DNA of the three subspecies suggests them to be morphologically similar but behaviourally different variants of the same species (Roehrdanz, 2001).
DescriptionTop of page
A detailed technical description of the larva and a key separating it from other larval Anthonomini is provided by Ahmad and Burke (1972): mature larva 5.6-8.1 mm in length, robust, thickest through middle abdominal segments; white in colour, distinctly curved, tapered toward posterior end. Asperities, resembling tubercles on thorax, minute and resembling spines on posterior segments of the abdomen. Head is pale yellowish-brown in colour, unretracted, slightly broader than long, and broadly rounded posteriorly, with one pair of stemmata (ocelli) and several pairs of setae. Pronotal shield lightly pigmented. Abdominal segment 1-7 with 3 dorsal folds. Terminal abdominal segment subconical, anal opening ventral.
The pupa was described and figured by Burke (1968) who also provided a key to the known pupae of the tribe Anthonomini, including A. grandis. The pupa is white in colour, with a body length of 6.6-7.4 mm. Abdominal segment 9 bearing 2 posterior processes (urogomphi).
Anderson (1968) described the pupae of the two subspecies, A. grandis grandis and A. grandis thurberiae. He recorded differences in the relative length of a pair of tubercles on the rostrum, in the number of well-developed setae on the postero-lateral areas of the prothorax and in the spacing of the setae on the antero-lateral areas of the prothorax.
Body length 5.5-8.0 mm in length, reddish-brown in colour. Antennae slightly paler, sparsely covered with long, whitish, decumbent pubescence, denser along midline and laterally on pronotum, not intermixed with erect setae. Antennal funicle 7-segmented, basal segment much longer than second, apical segment distinct from club, club elliptical, not very loosely articulated. Scrobes long, straight, directed towards and terminating close to anterior margin of eyes, not approximate beneath. Eyes large, convex, subspherical, sloping dorsally in front. Pronotum very coarsely punctured. Elytra coarsely punctate-striate, interstices 4 and 5 tuberculate apically, interstice 3 without post-median tubercle or patch of long, reddish-orange setae. Profemora bearing 2 distinct spines, inner spine twice size of outer, mesofemora with outer spine greatly reduced, and absent in metafemora, metatibiae straight in both sexes, without spines, tarsal claws bifid. Abdomen with sutures between sternites straight, pygidium convex and not excavated.
Keys to North American Anthonomus spp., including A. grandis were provided by Dietz (1891).
Jones and Burke (1997) keyed five species in the A. grandis species group, three of which were new.
DistributionTop of page A. grandis is indigenous to Central America and probably originated in southern Mexico and Guatemala. It spread into the USA, where it was first recorded in Texas in 1898, and also the Caribbean (Burke et al., 1986). It has since spread to all cotton-growing areas of the USA and recently to Brazil (EPPO, 1992) and other countries in South America.
The distribution of A. grandis was mapped by IIE in 1993.
See also CABI/EPPO (1998, No. 16).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
Risk of IntroductionTop of page A. grandis is listed as an A1 quarantine pest by EPPO (OEPP/EPPO, 1979), and also has quarantine significance for Africa, Asia and the Caribbean. This is clearly justified by the massive economic importance of the pest in the Americas, and problems associated with its control. As A. grandis is essentially a subtropical pest, the cotton-growing area at greatest risk in the EPPO region would be the Mediterranean zone. It is questionable whether the boll weevil could survive the low winter temperatures of the Central Asian cotton-growing areas of the former USSR. For many years, the boll weevil 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 south-western USA. In the early 1950s, however, it gradually moved westward into some of these formerly unoccupied areas, confirming the risk to Mediterranean countries (EPPO, 1992).
Especially in arid areas, thermal convection may disperse flying adult weevils for long distances of up to 72 km. In central Texas, USA, greatest dispersal occurs from mid-August to September. In international trade, boll weevils may be carried with cotton seeds or bolls, with raw cotton and various cotton products (EPPO, 1992).
Hosts/Species AffectedTop of page The principal host of A. grandis grandis is upland cotton, including Gossypium barbadense and and wild species of Gossypium. Significant reproduction of these boll weevils is also observed in the field on a number of wild Malvaceous hosts, including weeds. Marginal reproduction has been observed on the ornamental plant Hibiscus syriacus (rose of Sharon). A. grandis thurberiae mainly feeds on the wild host G. thurberiae, but also on cultivated cotton (EPPO, 1992). For more information on hosts, see Cross et al. (1975).
In the EPPO region, cotton is the only host to be considered, although wild Malvaceous hosts may act as possible reservoirs of the pest (EPPO, 1992).
Growth StagesTop of page Flowering stage, Post-harvest
SymptomsTop of page The early stage of attack is recognizable by a small puncture (either egg or feeding puncture) at the side of the flower bud. The bracteoles subsequently spread out, whilst the buds turn brown in colour and fall off. In later stages, flowers turn a yellow colour and fall to the ground, as do small bolls. Large, punctured bolls usually remain on the plant, but will be of poor quality (EPPO, 1992).
Further information on symptoms is provided by USDA (1962) and Cross (1973).
List of Symptoms/SignsTop of page
|Inflorescence / external feeding|
|Inflorescence / fall or shedding|
|Inflorescence / internal feeding|
|Inflorescence / rot|
Biology and EcologyTop of page 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. Negligible oviposition occurs before diapause, but diapausing females of approximately 30 days old often become reproductive. In Texas, USA, peak emergence of overwintered adults occurs in mid-May. They feed on developing cotton foliage and the females lay eggs singly in cotton flower buds. In cases of high weevil populations and shortages of buds, two or more eggs may be laid in one bud; however, this is of minor significance as only one weevil matures in a flower (EPPO, 1992).
Late in the season, eggs are laid both in flower buds and in young bolls. Eggs hatch in 3-5 days; 50-51 hours is the minimum incubation time at 30°C. The larvae feed for 7-12 days inside the flower or boll and then pupate for 3-5 days. The emerging adults cut their way out of the flowers or bolls, and mate after feeding for 3-7 days. Females begin egg-laying within 20 minutes of mating, depositing one egg per hour in daylight. Successive multiple matings can occur, the females being attracted by a male pheromone (EPPO, 1992).
A. grandis grandis migrates and hibernates in forest litter or on various Malvaceous hosts, including volunteer and regrowth cotton in warmer areas. A. grandis thurberiae has never been found in litter, but diapauses as an unfed adult and remains trapped in the larval cell in the wild host (Thurberia thespesioides) until the summer rains (100-175 mm) free it. On this host, A. grandis thurberiae has only one small and one major generation per year. The Mexican boll weevil (intermediate form) survives in larval cells in cotton bolls, but adults have also been found overwintering in suitable litter (EPPO, 1992).
Total development periods recorded in the laboratory were 17 and 88 days for the Mexican boll weevil and 17.5 and 72.5 days for A. grandis thurberiae at 30 and 15°C, respectively. For both subspecies, a temperature of 35°C prolonged the developmental period. In Arizona, USA, high temperatures during June to August were reported to suppress boll weevil populations (EPPO, 1992).
There is extremely high mortality in A. grandis populations, with approximately 95% of the hibernating adults dying from heat, dry weather, and predation by birds and insects. Without such natural interference, the offspring of a single pair of boll weevils could amount to several million in one season (EPPO, 1992).
Natural enemiesTop of page
Notes on Natural EnemiesTop of page Geographical and phenological patterns in the mortality of immature stages of A. grandis grandis were observed within cotton buds in three regions of Texas, USA, during 1983. Predation was the dominant factor contributing to boll weevil mortality in cotton in the east-coastal region, accounting for an average of 58% mortality. The ant, Solenopsis invicta, was the major predator of the boll weevil. In the mid-western region, desiccation accounted for 57% of immature weevil mortality. In the north-central region, boll weevil mortality was almost equally distributed among parasitism (23%), predation (23%) and desiccation (30%). Parasitism occurred most often in the north-central region, although it was not the dominant mortality factor in any region. Bracon mellitor (Hymenoptera) was the major parasitoid of the boll weevil. Average boll weevil mortality occurring in the egg stage was <8%. Mortality attributable to disease from the larval to the teneral adult stage was <9% in all three regions. Total mortality was fairly equal among the geographical regions; total mortality was 82% in the north-central region, 71% in the mid-western region, and 64% in the east-coastal region (Sturm and Sterling, 1990).
Fernandes et al. (1994) studied ant predators of A. grandis between cropping seasons in Sao Paulo, Brazil, during 1991. Some 20% of active A. grandis adults that had been experimentally distributed on the ground of cotton fields were attacked and removed by foraging ants. The native ant, Pheidole oliveirai, was by far the most efficient predator, accounting for 94% of predation. The potential benefit of suppressing overwintering adults of A. grandis during the between-season period was mainly that of reducing the risk of high-level infestations during the next cropping cycle.
Field experiments were carried out in Sao Paulo, Brazil, during 1990-1991 to evaluate the levels of parasitism of A. grandis by B. mellitor in six different cotton varieties. The rate of parasitism was greatest in cultivar La 780-843FR (Soares and Lara, 1993). Pierozzi and Habib (1993) collected four parasitoids from cotton squares and fruits infested by A. grandis in Sao Paulo (Bracon ssp., B. vulgaris, C. grandis and Eupelmus cushmani). They were reared in the laboratory at 25 ± 2°C and 70 ± 10% RH.
Morales-Ramos and Cate (1993) found that the potential of Heterospilus megalopus as a biological control agent was limited by its low fecundity and rate of increase.
The pteromalid, Catolaccus grandis, attacks the final-instar larvae and pupae of A. grandis in the USA.
The braconid parasitoid B. thurberiphagae attacks A. grandis thurberiae in the USA (Rojas et al., 1995).
Impact SummaryTop of page
|Fisheries / aquaculture||None|
ImpactTop of page A. grandis is the most costly insect pest of US cotton. Based on trials from 1945 to 1980, Schwartz (1983) calculated that the potential loss due to A. grandis was 51% in the USA. With optimum control measures, losses would be 21%. Since its entry into Texas in the 1890s from Central America, the boll weevil has destroyed and reduced the quality of several billion US$ worth of cotton, averaging over 3 million hectares. Losses of 8% annually are estimated for this area. A. grandis first appeared in Georgia, USA, in 1915, causing cotton production to decline rapidly from a historical high of 2.8 million bales in 1914 to 600,000 bales in 1923. During the 1970s, USA cotton producers lost US$ 200 million or more annually, whilst boll weevil suppression cost an additional US$ 75 million annually. A. grandis is also the target for ca 30% of all insecticides used in US agriculture. The loss of US$15 billion has been credited to A. grandis since 1982 (NCRTF, 1973; EPPO/CABI, 1992). In 1982 in the USA, the total area affected by A. grandis was 2,082,354 ha of which 1,522,152 ha were treated. The cost of treatment was $9.14/ha and a 2.24% crop loss (or 70,938 t) was estimated to occur in spite of this (King et al., 1988). In Georgia, USA, 127,515 ha of cotton required control measures and this area was treated with insecticides (Lambert et al., 1989). In the early 1990s, losses ranged fom $150 million to $300 million annually, depending on the infestation severity, acreage and the price of cotton (Smith and Harris, 1994).
In 1995, A. grandis reduced cotton yields by 1.66% in the USA (Hardee and Herzog, 1996). However, due to successful eradication of the pest in Georgia during 1995, substantial economic and environmental benefits have been recorded. In 1995, yields of 2 million bales were produced on 1.5 million harvested acres (59% more than in 1994), representing a record total revenue. The mean number of insecticide treatments decreased from 6.48/ha before eradication to 5.4/ha afterwards. In most cases, the pesticides used are more specific, and the amount of active ingredient applied during each treatment has been reduced (Haney et al., 1996). In Mississippi, control of A. grandis by cultural methods resulted in fibre yield being higher by 38 kg/ha in spite of the fact that the frequency of applying control agents was reduced (Hamer et al., 1983).
Cotton entomologists in the Cotton Belt of the USA have annually estimated losses and costs due to insect attack. A. grandis has been classed as the major pest four times since 1979 (Williams, 1997).
Vargas-Camplis et al. (1997) stated that A. grandis is the most important insect pest to cotton production in Mexico, particularly in the north-east.
Detection and InspectionTop of page Examine the side of flower buds of cotton for small punctures caused by adult feeding or ovipositing. Open up flowers or bolls of cotton to search for small, whitish-coloured, strongly curved, legless larvae, approximately 6-8 mm in length, or small whitish pupae.
Look for small (5.5-8.0 mm in length), reddish-brown weevils, covered with whitish pubescence on cotton plants.
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Publications on boll weevil control are numerous and include the reviews by Lloyd (1986), Pencoe and Phillips (1987) and Fisher (1989).
In a comprehensive review of cotton insect management in the USA by Ridgway et al. (1983), two main control strategies are outlined, together with the supporting technology: field-by-field management in relation to economic thresholds; and area-wide population reduction, with the possibility of eradication (EPPO, 1992).
Elements of control strategies described by Cross (1973) and Davich (1976) include biological control utilizing natural parasitoids, predators and pathogens, resistant cultivars and suppression of possible overwintering sites.
A pilot Boll Weevil eradication experiment in the south of Mississippi, USA, during 1971-1973 was followed by another eradication trial in North Carolina, USA, during 1978-1980 to test the feasibility of eradicating the boll weevil with available techniques. Since then, the US Boll Weevil Eradication Project has conducted successful eradication programmes in California, North Carolina and Virginia. By 1990 it had been extended to Arizona, Florida, and parts of Alabama and Georgia, as well as north-western Mexico (EPPO, 1992). An area-wide suppression programme has also successfully mobilized significant resources in Nicaragua (Swezey and Daxl, 1988).
High soil temperatures combined with dry conditions can desiccate immature boll weevils and reduce the germination and establishment of volunteer cotton. Studies performed during 1994-1996 in Texas, USA, by Smart and Bradford (1997), revealed that the use of a cotton stalk puller was a quick and efficient way to destroy cotton stalks and to leave pupae or larvae and cotton seed within the top 2 cm of the soil surface where soil temperatures can reach 54°C or more. Ploughing the cotton stalk residue placed the boll weevil larvae and pupae in a dark and generally moist environment which may be conducive for over-wintering in south Texas and north-eastern Mexico.
Studies were undertaken in north-east Arkansas, USA, in 1996 to evaluate the feasibility of incorporating a spring trap crop-pheromone tactic into an A. grandis eradication programme for cotton. Trap crops were successfully installed using cotton transplants and set in the field using a high speed transplanter. The transplanted cotton, baited with 10 mg boll weevil pheromone lures and sprayed with ULV malathion applications twice-weekly, was three weeks earlier in development than the commercial crop and continued to be attractive to boll weevils even after the commercial crop began fruiting (Teague and Tugwell, 1997).
Cultural control strategies for A. grandis grandis on cotton in Texas, USA, were discussed by Slosser (1996). In the spring, delayed, uniform planting between late May and early June formed the basis for cultural control. During the summer, planting cotton on sloped beds, in an east-west row direction, was used to increase exposure of fallen squares to high soil temperatures, which kill larvae inside the squares. In the autumn, plant growth regulators can be used to remove squares and small bolls by late September. This reduces the proportion of the boll weevil population entering diapause and surviving the winter. Complete elimination of winter habitat or modification of the habitat by destroying only the leaf litter where the boll weevils are overwintering are two options to reduce winter survival.
A review of how farming systems and practices have influenced the evolution of the cotton-boll weevil agroecosystem is provided by Fisher (1989).
Attempts to apply classical biological control in the USA started in 1904 when a predacious ant, Ectatomma tubercuatum was imported from Guatemala, but it failed to become established. Attempts to introduce known parasitoids of A. vestitus from Peru during 1941-45 also failed, as did attempts to establish Bracon kirkpatricki, a parasitoid of Pectinophora gossypiella in Kenya (Clausen, 1978; Cate, 1985). More recently, explorations were carried out in Mexico and two promising parasitoids were imported. One of them, Urosigalphus monotonus (Braconidae) failed to breed indoors, but the other, Catolaccus grandis (Pteromalidae) was successfully bred and released, but did not become established. The possibilities of enhancing the impact of the native parasitoid, Bracon mellitor, was investigated, as was the possibility of exploiting the introduced fire ant, Solenopsis invicta. Since most native natural enemies are not specific to A. grandis and do not respond to changes in its population density, and introduction of species from Mexico has been unsuccessful, control efforts have recently been focused on attempts at eradication (Cate, 1985).
Purified spores of Metarhizium anisopliae and Beauveria bassiana were tested for their pathogenicity against A. grandis collected from a cotton field in Sao Paulo, Brazil. After 7 days all the inoculated weevils were dead. No differences in pathogenicity were detected between strains of B. bassiana which had been isolated from A. grandis, the curculionid Cosmopolites sordidus and the scolytid Hypothenemus hampei (Camargo et al., 1985).
Bleicher et al. (1994) evaluated the action of B. bassiana in conjunction with insecticides against A. grandis on cotton in Ceara, Brazil. Deltamethrin at a low dosage in combination with the fungal pathogen was as effective as deltamethrin alone at a full dosage.
Morphological mutants of M. anisopliae var. majus and M. anisopliae var. minus were obtained following mutagenic treatment with 8-methoxypsoralen and UV light. Adults of A. grandis were susceptible to both strains and their mutants, although the morphological mutants had lower pathogenicity than the parent strains (Oliveira et al., 1994).
The use of the spores or crystals of Bacillus thuringiensis (strain San Diego) as an insecticide against insect pests of cotton, potato, lucerne and maize has showed that A. grandis can be controlled with this agent (Herrnstadt and Soares, 1989).
A formulation of a feeding substrate containing cotton products, grandlure (boll weevil pheromone), a sticker and UV protectant (Nufilm 17), and B. bassiana, was developed in the laboratory for activity against A. grandis grandis. The formulated material was evaluated against weevil populations in the field in non-cotton habitats, bait stations, in regrowth cotton and in early-season cotton against overwintered adults. Significant mortality caused by B. bassiana was observed in all evaluations. When this mycoinsecticide was applied against emerging overwintering adults in 1989 and 1990, lint yields increased by 74 and 113% respectively, compared with untreated controls (Wright and Chandler, 1992).
Wright and Knauf (1994) evaluated the effectiveness of Naturalis-L, a commercial biological control product that provides excellent control of many major cotton pests, and which can be applied by conventional and aerial application equipment. Naturalis-L, which contains conidia of B. bassiana (strains ATCC 74040, ARSEF 3097, FC1 7744), was tested against overwintering adults of A. grandis grandis in the spring and throughout the cotton production season for control of adults in Texas, USA, during 1991-1992. Naturalis-L was inferior to a combination of bifenthrin and acephate. Integration of Naturalis-L for early season protection and insecticides for infestations occurring after bloom provided the best protection and lint yields (Wright, 1993).
Several authors have evaluated the augmentative release of the parasitoid C. grandis for control of A. grandis in cotton crops in Texas, USA. Summy et al. (1992) conducted augmentative releases of female parasitoids during 1991. Parasitism was concentrated among third-instar host larvae, the majority of which (98.7%) occurred in abscised cotton squares. Results demonstrated the ability of C. grandis to search and reproduce within the release environment, and to effectively parasitize a distinct segment of the host population. Slosser et al. (1995) reported parasitism rates of 65-74% for third-instar larvae after C. grandis was released during 1994, and it also did not displace the native parasitoid B. mellitor. Morales-Ramos et al. (1995) reported mortality estimates from parasitism of 65-95% (1992) and 22-87% (1993). Boll weevil survival (from egg to adult) in the control cotton fields ranged from 72.8 to 78.2%, compared with 0.5 to 11.8% in treated fields. Summy et al. (1995) showed that C. grandis can suppress and maintain boll weevil infestations at subeconomic levels when augmented in sufficient quantities during the period in which the first and second host generations normally develop. Natural enemy augmentation was also investigated as a means of suppressing infestations of A. grandis in stands of undestroyed cotton during the post-harvest fallow season. Augmentative releases of C. grandis and B. mellitor at relatively high rates (approximately 4000 and 2000 mated female parasitoids per hectare, respectively) was accompanied by a significant increase in densities of the former and a slight increase in the latter. Parasitism by C. grandis was largely concentrated among third-instar larvae infesting abscised cotton squares, but caused appreciable mortality (90.6%) within this segment of the host infestation. The relatively high incidence of host mortality caused by parasitism within this infestation served to destroy significant numbers of immature weevils that appear to have been predisposed to successfully overwinter (Summy et al., 1995).
Vargas-Camplis et al. (1997) studied the control of early boll weevil infestations by releases of C. grandis females, compared to insecticide spraying according to economic thresholds in Mexico during 1996. A total of 14 releases were made twice a week, except the last one which was made after an interval of 7 days. An average of 950 adult females per hectare were released. Results obtained showed that C. grandis was the main mortality factor for third-instar larvae, the highest mortality being obtained during the early season, followed by the mid-season.
General accounts of resistance to A. grandis in cotton can be found in Smith (1992). El-Zik and Thaxton (1996) described the characteristics of Tamcot Sphinx, a boll weevil-resistant cultivar with similar levels of resistance to Tamcot HQ95. It has significantly higher fibre quality and increased yield potential compared with previously released Tamcot cultivars.
Some primitive cotton accessions from Mexico identified in the USA as significantly reducing oviposition punctures, and other lines identified as significantly reducing boll weevil populations in the field were used in resistance breeding. After crosses with the cultivars Stoneville 213, PNH3 and CNPA Precoce 2, resistant lines with good fibre and yield characteristics were obtained (Carvalho et al., 1996).
Carbamate, organophosphate and pyrethroid insecticides were compared for control of A. grandis grandis on cotton in Arkansas, USA, during 1994 and 1995. Pyrethroids gave better control than organophosphate and carbamate insecticides.
Martin et al. (1996) performed topical bioassays of 11 insecticides against 22 field collections of A. grandis grandis collected from cotton in 11 locations in Louisiana, USA. There was no conclusive evidence of field resistance to any of the insecticides bioassayed, although LD50 values for cypermethrin and malathion were highly variable.
Spurgeon et al. (1997) investigated patterns of efficacy by boll weevil insecticides at different times after treatment application and for selected exposure times in the laboratory. Mortality continued to increase between observations at 24 to 72 hours after initial exposure regardless of duration of the exposure or the insecticide used. However, changes in mortality between observation times were greater for fipronil than for other materials. When the duration of exposure was <12 hours, mortality was typically reduced. Fipronil gave high levels of mortality immediately after treatment application, but demonstrated greater activity than the other materials when initial exposure was delayed for 24 hours.
Jones and Wolfenbarger (1997) studied malathion ULV spraying in boll weevil eradication programmes in Texas and Mississippi, USA, during 1995-1996. Applications were compared under drought and humid conditions by using a bioassay with laboratory-reared boll weevils on collected cotton leaves. Mortality dropped from 100% after 48 hours exposure to 90% four days post-treatment and to 35% after 11 days under drought conditions. Under humid conditions, mortality remained at 100% until seven days after treatment, at which time a second application was made. Alkaline dew was concluded not to be an important factor in the decomposition of malathion, although rain was found to be a cause of reduced toxicity.
Eight insecticides were compared for their effects on A. grandis, Spodoptera exigua and beneficial insects during cotton production in Texas, USA, during 1996. Insecticides generally caused an increase in aphid and S. exigua infestation and reduced beneficial arthropod numbers by 50-86%. Insecticides reduced boll weevil damage and increased cotton lint yields by 157.2-336.5 kg/hectare. Each foliar insecticide treatment was applied to non-transgenic and transgenic B.t. (Bacillus thuringiensis) cotton cultivars to evaluate effects on target and non-target insects. The transgenic B.t. cotton averaged 76.3 kg/hectare more lint than the non-transgenic cultivar. Overall, numerical yield increases over the non-transgenic untreated cotton ranged from 112 kg/hectare (transgenic and treated) up to 455.5 kg/hectare (non-transgenic and treated) (Parker and Huffman, 1997).
The use of pheromones in A. grandis management relies on trapping with the pheromone grandlure (Benedict et al., 1995). This is done early in the season to time the first insecticide applications (Henneberry et al., 1988). Trapping is also used to suppress low-level boll weevil populations (Leggett et al., 1988).
Since the eradication of A. grandis from nine states of the USA, post-eradication surveillance with pheromone traps has been used to protect these areas from re-infestation (Parker, 1997). A summary of 30 years of extensive research on semiochemicals and their effects on A. grandis in cotton crops is provided by Hardee and Mitchell (1997).
The Boll weevil Attract and Control Tube (a bait stick containing grandlure, phagostimulants and an insecticide) was evaluated in Colombia, Brazil and Paraguay during 1994-1996. Results from using these bait sticks in IPM programmes have shown high levels of boll weevil attraction and control, delayed initiation of weevil sprays, reduced number of weevil control sprays required to produce a crop, reduced crop damage, increased square retention, increased cotton fibre production and greater operating profits from insecticide savings and fibre production. Use of the bait sticks can attract and kill out-of-season or between-crop weevil populations in Colombia, Brazil and Paraguay. In semi-tropical and tropical countries, boll weevils remain active throughout the year and this provides a unique opportunity for attract and control tactics. Bait sticks have been used in quarantine programmes to prevent the boll weevil from becoming established in cotton growing zones of Argentina and Bolivia (Plato and Plato, 1997).
Fuchs et al. (1997) surveyed 1552 cotton producers in Texas, USA, to obtain baseline data on acreage, pest management practices, insecticide use and pests targeted by insecticides in 1994. IPM producers were defined as producers who used scouting, economic thresholds and 70% of the weighted management practices important to IPM in the region. Based on this definition, 64% of the cotton producers qualified as IPM producers.
Release of sterile males has also been used in boll weevil suppression (Haynes and Smith, 1989; Villavaso et al., 1989).
EPPO recommends (OEPP/EPPO, 1990) that cotton-growing countries should prohibit importation of seeds or bolls of cotton from countries (or states in the USA) where A. grandis occurs. Raw cotton from the same origin (including waste fabric, waste cotton, cotton seed cake, meal, bags that have been used as a container for lint or any form of unmanufactured cotton) should be fumigated with phosphine (FAO, 1983). There is no obvious pathway from EPPO countries not producing cotton to those mainly concerned about the pest, so no special measures are recommended for them except to list A. grandis as a quarantine pest (OEPP/EPPO, 1990).
In South America, where the boll weevil is liable to spread to new areas, networks of pheromone traps have been established along the Paraguay-Brazil border to intercept the pest (Whitcomb and Marengo, 1986).
ReferencesTop of page
Ahmad M; Burke HR, 1972. Larvae of the weevil tribe Anthonomini (Coleoptera, Curculionidae). Miscellaneous Publications of the Entomological Society of America, 8(2):31-81.
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