Morphological Variability of the Cotton Boll Weevil in the Principal Cotton‐Growing Region of Argentina

Although a great deal of research has been conducted on the boll weevil, Anthonomus grandis grandis Boheman, originally a Mesoamerican insect, in temperate cotton, Gossypium hirsutum L., growing regions of the United States, relatively little is known about boll weevil ecology in the subtropics and tropics, which extend from South Texas to Argentina. Unlike in temperate regions, boll weevils do not necessarily diapause in the subtropics. Rather, they are active and can reproduce year-round provided that adequate host plants are available. Instead of predators (excluding limited areas where the imported fire ant, Solenposis invicta Buren, has become established) and cold winter temperatures being key factors behind boll weevil population dynamics, the availability and quality of food sources are most important. During the cotton-growing season, boll weevil populations respond to the changing quality of the cotton plant, and component parts, which can profoundly affect gravidity, fecundity, and longevity, and susceptibility on the plant to injury from both feeding and oviposition. Immature boll weevils developing within fallen squares are often killed by heat and associated desiccation unless they are buried and insulated by in-season cultivation. During and after harvest operations, substantial numbers of boll weevils remain in the field, presumably in cotton plant debris, including fallen squares and bolls. Although heat and desiccation also kill these weevils until conditions cool as the typically mild subtropical winters approach, weevils inside fruiting bodies on the soil surface can survive better than those buried by tillage. In the subtropics, boll weevils can reproduce during winters on volunteer cotton plants and a limited number of malvaceous plant species. Overwinter survival, however, is likely facilitated more by nutritious food sources enabling longevity that spans the cotton-free period. Some common subtropical food sources that can sustain adult boll weevils in this way are the endocarps of oranges, Citrus sinensis (L.) Osbeck.; grapefruit, C. paradisi Macfad.; and prickly pear, Opuntia engelmannii Salm-Dyck ex. Engel.; and other such food sources are possible. Although some researchers have maintained that boll weevils “migrate,” long-distance boll weevil movement during the off-season is probably passive and opportunistic because nutritious food sources for overwintering already exist in most subtropical cotton-growing areas. Instead, boll weevils generally remain in the area, surviving winter in citrus orchards, and possibly other places where nutritious food is available. Flaws with the efficiency of the commonly used boll weevil trap design, and the field sampling method used in South Texas (and possibly other areas) are discussed, as well as weaknesses of the boll weevil spray regime that relies on pre-emptive sprays and sprays triggered by thresholds determined by sampling randomly-selected cotton squares. An alternative, proactive spray approach based on the relationship of boll weevil populations to the changing nutritional quality of cotton fruiting bodies is described, as well as other potential in-season and off-season control tactics, including careful choice of planting date, burial of post-harvest cotton debris, citrus orchard sanitation, and mass-trapping for adult boll weevils in overwintering “hot spots” where boll weevils accumulate until cotton is planted in the spring.

BackgroundTo control the boll weevil Anthonomus grandis grandis (Coleoptera: Curculionidae), a key pest of cotton in the Americas, insecticides have been intensively used to manage their populations, increasing selection pressure for resistant populations. Thus, this study aimed to detect insecticide resistance and assess insecticide control failure likelihood of boll weevil populations exposed to malathion, profenophos + cypermethrin, and fipronil insecticides.ResultsTwelve populations of the boll weevil were collected from commercial cotton fileds of the state of Bahia, northeastern Brazil. These populations were exposed to malathion, profenophos + cypermethrin mixture, and fipronil, at their respective maximum label dose for field applications. Three replicates of 10 adult beetles were exposed to the insecticides and mortality was recorded after 24 h treatment. The control failure likelihood was determined after 48 h. Highest median lethal times (LT50) were observed for malathion and the profenophos + cypermethrin mixture. Resistance to at least one insecticide was detected in 11 populations; three populations were resistant to malathion and profenophos + cypermethrin; seven were resistant to all insecticides tested. The resistance levels were low (< 10-fold) for the three insecticides. Among 12 populations tested, 58% of them exhibited significant risk of control failure for the insecticides malathion and profenophos + cypermethrin. The insecticide fipronil was efficient for the control of the boll weevil in 83% of the populations.ConclusionsThe results confirm the significant risk of insecticide control failure in the boll weevil populations to the main compounds used in the region. Thus, proper insecticide resistance management plans are necessary for the boll weevil in the region, particularly for malathion and profenophos + cypermethrin insecticides.

Cotton pests damaging fruiting bodies (squares and young bolls) are difficult to control and their damage results in direct yield loss. Small growers, with low technological inputs, represent a large portion of cotton growers worldwide comprising more than 76 countries; they rely mainly on cultural practices to counteract pest attack in their crops. Boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), oviposition involves puncturing cotton squares and young bolls, causing abscission. We examined the impact on boll weevil population of collecting abscised cotton fruiting bodies and clipping plant terminals at 50% boll maturation in the field during two cotton‐growing seasons and under field cage conditions. Greatest numbers of damaged squares occurred ca. 117 days after planting and clipped plants resulted in reduction of abscised structures and adult boll weevils compared with non‐clipped plants, irrespective of cotton variety. Damaged young bolls were found ca. 128 days after planting in 2009 and 2011, but clipping had no effect. Numbers of boll weevils found in plants of the varieties BRS 201 and BRS Rubi (both in 2009) and BRS Rubi (in 2011) were, respectively, 13‐, 17‐, and 20‐fold greater when clipping plus collecting abscised fruiting bodies were not practiced. Furthermore, the average percentage of the boll weevil parasitoid Bracon vulgaris Ashmead (Hymenoptera: Braconidae) emerging from abscised and collected structures was similar between clipped and non‐clipped plant terminals in both seasons. Clipping plant terminals did not result in yield reduction and reduced adult boll weevil production. Collecting abscised reproductive structures, clipping plant terminals, and using both practices together reduced boll weevil populations by as much as 63, 57, and 79%, respectively, in cage trials. Thus, these practices cause significant impact on boll weevil populations and are feasible of adoption, especially for smallholder cotton growers.

Flat and cylindrical adhesive boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), pheromone traps captured significantly more (P < or = 0.05) boll weevils than the Hercon (Hercon Environmental, Emigsville, PA) trap during the late cotton-growing season, and larger adhesive areas were associated with higher captures; a flat plywood board collected the most boll weevils because it had the largest surface area. The flat board trap, chosen for measuring large late-season adult boll weevil populations common to the Lower Rio Grande Valley of Texas in 2000 and 2001, collected more (P < or = 0.05) weevils when deployed in proximity to natural and cultivated perennial vegetation, and mean numbers of captured boll weevils were higher (P < or = 0.0001) on the leeward sides of the board traps than on the windward sides. The board trap had an estimated potential capacity of approximately 27,800 boll weevils, and the large capacity of the board trap allowed for more accurate measurements of large adult boll weevil populations than the more limited Hercon trap. Measurement of adult boll weevil numbers after the routine field operations of defoliation, harvest, shredding, and stalk-pulling, demonstrated that large populations of boll weevils persist in cotton fields even after the cotton crop has been destroyed. Increases (P < or = 0.05) in the percentage variation of trapped boll weevils relative to the numbers collected just before each field operation were observed after defoliation, harvest, shredding, and stalk-pulling, but the percentage variations followed a quadratic pattern with significant correlation (P < 0.0001; 0.59 < adjusted r2 < 0.73). Numbers of adult boll weevils caught on board traps deployed at 15.24-m intervals on windward and leeward edges of cotton fields suggested that boll weevil populations in flight after field disturbances might be affected by large-capacity trapping.

The role of the boll weevil (Anthonomus grandis Boh.) resistant cotton (Gossypium hirsutum L.) strain, frego bract, in the management of cotton pests was investigated in 22 fields in Yalobusha County, Mississippi in 1971. The objectives were (i) to measure boll weevil population suppression when frego bract cotton was used with and without a reproduction‐diapause program the previous year, and (ii) to determine if the resistant cotton strain could materially aid in removing the boll weevil as the key pest in cotton fields. If so, one could potentially use integrated control for other cotton pests and also conduct research on pest management systems. The use of the frego cotton suppressed the boll weevil population 69% and 79%. respectively, with and without a diapause program. In addition, the beginning of weekly applications of insecticides for boll weevils was delayed 4 weeks longer in the frego fields than in nonfrego fields. We were able to go through the period of peak activity of the bollworm complex (Heliothis spp.) before we needed boll weevil insecticides in the frego. However, in the nonfrego fields we were applying boll weevil insecticides before and during this time. Thus, frego can be used in research on pest management systems while it continues to be tested for use as a resistance character for commercial varieties.

In 1970 four farms located in different parts of Mississippi each were planted to 4 to 8 ha of cotton (Gossypium hirsutum L.), homozygous for frego bract ( fg fg ), and to an approximately equivalent acreage of a nonfrego commercial variety. Cottons with frego bract have shown resistance to boll weevils (Anthonomus grandis Boh.) when grown in small plots. Our 1970 tests were designed to measure the cumulative effects of a fregobract cotton, designated M‐64, on boll weevil populations when this cotton was grown in large acreages and when the resistance was measured over three or four insect generations. Results from these tests will be used to assess the role of cottons resistant to boll weevil in an integrated approach designed to eradicate this insect. A pilot scale boll weevil eradication program is now underway in Mississippi.In the frego‐bract cotton boll weevil oviposition, an indirect measure of population, was suppressed 66, 71, 75, and 94% below that in the nonfrego varieties. The variation in suppression was due to different numbers of overwintering weevils and to various control measures used during the season. On two farms no insecticides were required for boll weevil control in the frego‐bract strain. The frego‐bract strain suppressed the population 94% on the farm with the smallest number of overwintering weevils. Thus, oviposition suppression was greatest where it can be of the most use in an eradication program.Fiber properties and yields of the frego strain were adequate for a nonbiased test of the boll weevil resistance attributed to frego bract.

A glass vial technique was developed to estimate the toxicity of oregano phosphorus, carbonate, cyclocliene, and pyre throed insecticides to the boll weevil, Anthonomus grandis grandis Bohemian, and to monitor field populations for tolerance to such insecticides. In tests in which responses of the USDA Ebony strain boll weevils were compared With those collected in the field in the Bravos Valley, TX, in 1988, tolerance to oregano phosphorus, pyre throed, and carbonate insecticides was demonstrated. The usefulness of the glass vial technique for monitoring tolerance was confirmed in 1991 and 1992 by field data from Texas, Arkansas, Mississippi, Oklahoma, and Sonora, Mexico. These tests indicated tolerance to oregano phosphorus and pyre throed insecticides in several boll weevil populations. Tolerance monitoring may be a useful technique in the implementation of boll weevil eradication programs.

In 1962 research was begun in northern Sonora, Mexico, to determine the amount of damage caused by boll weevils, Anthonomus grandis Boheman, occurring in cotton fields as near as 27 miles to fields in Arizona. This research involved the establishment of ecological relationships among boll weevil populations in Sonora, in the old infested areas of the United States, and in southern Arizona, where a variety of the boll weevil, the thurberia weevil, A. grandis thurberiae Pierce, occurs on a wild cotton, Gossypium thurberi Todaro. Square damage in the Mexican cotton reached an areawide level of 10% in late August and severe yield losses occurred in several fields. In Arizona, incipient infestations of thurberia weevils developed in several cotton fields by September 5. It was determined that boll weevils in Sonora developed diapause and entered surface ground trash to survive the winter, The thurberia weevil is not known to hibernate in ground trash. In addition, evidence of considerable winter survival of the Sonora boll weevils in pupal cells within old bolls was observed in northern Sonora cotton fields, This is the only known manner in which the thurberia weevil survives over Winter. Applications of methyl parathion to cotton fields in Sonora in late October and early November considerably reduced overwintering populations.

Understanding the critical host plant factors that determine oviposition behavior and survival of boll weevil, Anthonomus grandis grandis Boheman, on cotton, Gossypium hirsutum L., is important for developing successful pest management strategies. However, published information is both conflicting and limited regarding how different cotton fruit sizes affect boll weevil oviposition choices and subsequent larval survival to adulthood. Consequently, we used a standard based on fruit size diameter to evaluate boll weevil feeding and oviposition punctures, and survival to adulthood on 10 different cotton fruit sizes: squares of diameter 1.5–2.0 (pinhead), 3.0–3.5 (matchhead), 5–6, 7–8, or 9–10 mm; candle; and bolls of diameter 10–15, 15–20, 20–30, or >30 mm. Oviposition and feeding punctures were significantly affected by cotton fruit size. Females did not oviposit in pinhead squares. The fewest eggs were oviposited in boll sizes >30 mm. The highest number of eggs was recorded in square sizes of 5–6 and 7–8 mm. Boll weevil survival to adulthood was highest on square sizes of 7–8 or 9–10 mm (58.6–59.7%). No survival occurred in matchhead squares or bolls >30 mm. Duration of development was longest on boll sizes of 15–20 and 20–30 mm (18.2–18.8 d). The growth index (percentage immature survival divided by immature developmental time) of female boll weevils was 2.8-fold higher in 7–8- or 9–10-mm diameter squares than in 20–30-mm diameter bolls. This study will improve our capacity to develop methods to predict fruit losses and changes in boll weevil populations in the field, given a starting density of fruit suitable for oviposition, and a corresponding initial population density of weevils.

Six insecticide treatments were evaluated at the Macon Ridge Branch of the Northeast Research Station, Winnsboro, LA, to determine their efficacy in controlling the bollworm/tobacco budworm complex and boll weevils. Cotton was planted 18 Jun in plots consisting of 4 rows (40 inch centers) × 50 ft. Treatments were arranged in a RCBD with 4 replications. Treatments were applied with a high clearance sprayer calibrated to deliver 6 gal total spray/acre through Teejet X-8 hollow cone nozzles (2/row) at 46 psi. Insecticides were applied on 22, 26 Aug and 1 Sep against established populations of bollworms, tobacco budworms (primarily tobacco budworms) and boll weevils. Efficacy of the various treatments against these species was determined on 25, 31 Aug and 7 Sep by examining 50 squares/plot for evidence of feeding damage. Also numbers of larvae per 50 squares were recorded for the bollworm/tobacco budworm complex. The plots were mechanically harvested on 25 Oct to determine seed cotton yields. The test area received 0.57 and 0.20 inches rainfall on 1 and 6 Sep, respectively.

The efficacy of the organic insecticide Diatect II against boll weevil (Anthonomus grandis Boheman) in cotton (Gossypium hirsutum L) in the Lower Rio Grande Valley of Texas were assessed in small-plot field trials and greenhouse cage tests using azinphos-methyl treatments as a standard for comparison. Plastic sheets were placed in the furrows of the treated plots to retrieve boll weevils which dropped from the plants after being killed by the insecticides. Samples of live weevils taken by a tractor-mounted vacuum sampler revealed a modest, but significant, reduction in boll weevil populations in Diatect II plots. However, samples of dead weevils indicated that this reduction was due to movement of weevils out of the plots rather than to mortality. This interpretation is supported by greenhouse cage studies, where mortality in Diatect II treated cages was no greater than that in untreated control cages. The effects of insecticide treatments in small plots can be confounded easily and quickly by interplot movement of target insects. Although the relative effects of various compounds can usually be assessed by sampling the populations in plots soon after treatment, the best measure of efficacy is obtained by directly sampling insects that have died in the plot. This parameter is insulated from the effects of interplot movement, unless the toxicant is slow to immobilize the target insect. Taken together, our results indicate little efficacy by Diatect II against boll weevil under our test conditions.

Insecticide resistance in arthropods is an inherited trait that has become a major cause of insect pest control failure. Monitoring the level of susceptibility and characterization of the type of resistance of key pest species aims to determine the risk of resistance selection in time to take action to mitigate control failures. Seven populations of the boll weevil, Anthonomus grandis grandis, collected from cotton fields in the Semiarid and Cerrado areas of Brazil, were screened for their resistance to malathion and beta-cyfluthrin, insecticides widely recommended for control of boll weevil and other pests. The levels of adult mortality were variable for beta-cyfluthrin (0-82%) but invariant (100%) for malathion. Bioassays of concentration-mortality were used to determine lethal concentrations (LCs) for each insecticide. The LC-values corroborate the lack of resistance to field rates of malathion but high levels of resistance to beta-cyfluthrin from 62.7- to 439.7-fold. Weevils resistant to beta-cyfluthrin were found through genome sequencing to possess a kdr mutation through the L1014F substitution in the voltage gated-sodium channel gene. This study found boll weevil resistance to beta-cyfluthrin to be not mediated by carboxylesterases, but with cross-resistance to DDT and carbaryl, and kdr mutation as the major mechanism of the resistance in our samples. Caution is recommended in further use of beta-cyfluthrin against boll weevil due to potential resistance. Monitoring studies using other boll weevil populations are recommended to determine the geographic pattern and extent of pyrethroid resistance. © 2021 Society of Chemical Industry.

The boll weevil (Anthonomus grandis Boheman) is an insect pest of cotton that underwent a well-documented range expansion across the southeastern U.S. from Mexico beginning about 110 years ago. Eleven microsatellite loci were surveyed to infer the magnitude and pattern of genetic differentiation among boll weevil populations from 18 locations across eight U.S. states and northeast Mexico. Estimates of genetic diversity (allelic diversity and heterozygosity) were greater in Southern than Northern populations, and were greater in the west than the east among Northern populations. Boll weevil populations were genetically structured as a whole across the geographic range sampled, with a global F (ST) of 0.241. South-central populations exhibit classic isolation by distance, but evidence suggests that populations within the Eastern and Western regions have not yet reached genetic equilibrium. Gene flow appears to be relatively high among populations within the Eastern region. Population assignment data and estimates of gene flow indicate that migration between locations separated by < 300 km is frequent. The database of microsatellite genotypes generated in this study now makes it possible, through population assignment techniques, to identify the most likely geographic source of a boll weevil reintroduced to an eradication zone, which will help action agencies decide the most appropriate mitigation response.

Seasonal populations of boll weevils, Anthonomus grandis Boheman, were carefully sampled in a number of small cont iguous cotton fields where control programs with different inticides were being conducted. Records were also made of cotton fruiting and fruit damage by weevils in these fields and in untreated control areas to determine the relationships between boll weevil numbers, abundance of fruit, and boll weevil damage, as well as the effectiveness of the insecticidal programs. The organophosphorus compounds were generally more effective for the control of overwintered weevils than the other types of insecticides used, but continued emergence of boll weevils after squaring began during 1960 and 1961 reduced the effectiveness of programs depending on a single application for the control of overwintered weevils. Continuously high populations in the untreated areas resulted in greatly reduced boll set, but the emergence of large numbers of weevils in the treated fields which increased square damage temporarily did not reduce boll set. However, in the treated areas higher percentages of punctured Squares were usually followed by higher percentages of weevil damaged bolls. The rate of population increase from generation to generation and the amount of damage caused by each weevil depended to a great extent on the numbers of squares on the cotton and the intensity of competition for those squares. In untreated fields during 1960 and 1961 first generation increases over overwintered populations were about S-fold and 2-fold respectively.

A 2-yr study was conducted to evaluate the effect of ethephon (2-chloroethylphos- phonic acid) on efficacy of pheromone traps in monitoring fall and spring populations of adult boll weevils. The experimental procedure consisted of a grandlure pheromone strip placed in a boll weevil trap together with a 7.5-ml aqueous solution of ethephon at 0.1, 1, 10, and 100 ppm concentrations. Treatments also included traps with nothing, ethephon alone at each of the four concentrations, and grandlure alone. Traps were monitored twice a week, and ethephon solutions were replenished during each trap inspection. Trap catch was significantly affected by year, season, and treatments. Overall, significantly higher numbers of boll weevils were captured in 1996—1997 compared with 1997—1998. Average numbers of boll weevils captured in fall season were approxi- mately six times higher than the numbers captured in the spring season. Ethephon alone did not elicit a significant attraction to fall or spring populations at any concentration evaluated. However, the combination of ethephon and grandlure pheromone showed a distinct synergistic effect, enhancing the efficacy of pheromone-baited traps in monitoring fall migration of boll weevil populations. Ethephon at 1 and 10 ppm combined with grandlure were most attractive to fall-migrating weevils, capturing 20—35% more weevils than the grandlure alone. The combination of ethephon at 10 ppm and grandlure also had a significant effect on weevil attractancy for spring populations, but the results were not consistent between years. Data from this study clearly suggest that the addition of ethephon to grandlure can significantly improve trap attractancy and will aid in boll weevil monitoring and eradication strategies that aim at attacking the weevils during the fall, with some potential of improved attractancy in monitoring spring populations.