Sublethal effects of malathion on boll weevil (Coleoptera: Curculionidae) fecundity when maintained on cotton squares or artificial diet

Mated 3‐day‐old female boll weevils, Anthonomus grandis grandis Boheman, reared from field‐infested cotton (Gossypium hirsutum L.) squares were topically treated with an estimated LD₅₀ of malathion (2 μg) to assess its effects on fecundity, oviposition, and body fat condition. Two different food sources, cotton squares and artificial diet, were assessed in malathion‐treated and nontreated (control) weevils. The LD₅₀ caused ～50% mortality in the square‐fed malathion treatment, but the artificial diet‐fed malathion‐treated weevils were less susceptible. LD₅₀ survivors fed on the squares produced ≥ 9 times more chorionated eggs in the ovaries and oviposited ≥ 19‐fold more than survivors fed artificial diet, regardless of the malathion treatment. Boll weevils that survived a 2 μg LD₅₀ malathion and also fed squares were ～4.5‐fold leaner than diet‐fed weevils. Our findings demonstrate that non‐resistant boll weevils surviving a sublethal dose of malathion will reproduce without any delay or significant loss in fecundity, and the food source for which boll weevils are maintained when conducting these assays will directly affect the results. The significance of these findings and how they are related to the final stages of eradicating the boll weevil from the US are discussed.     

Suppression of Boll Weevil Infestations (Coleoptera: Curculionidae) Occurring on Fallow-Season Cotton in Southern Texas by Augmentative Releases ofCatolaccus grandis(Hymenoptera: Pteromalidae)

Augmentative releases ofCatolaccus grandis(Burks) were conducted in the Lower Rio Grande Valley of Texas in an attempt to suppress infestations of boll weevil,Anthonomus grandisBoheman, occurring in stands of “fallow-season” cotton (i.e., fields in violation of the 1 September stalk destruction deadline mandated by Texas law). In each of five release sites monitored during the study period (October, 1994–March 1995), augmentative releases ofC. grandiswere accompanied by an appreciable increase in the incidence of parasitized boll weevils (primarily third-stage larvae and pupae infesting abcised cotton squares) within a relatively brief time period. The relatively high incidence of host mortality caused byC. grandisin each release site was largely indispensible (i.e., would not have occurred in the absence of the parasite) and served to destroy significant numbers of immature boll weevils that appear to have been predisposed to successfully overwinter. The potential role of parasite augmentation in the management of the overwintering boll weevil population in southern Texas is discussed.     

Effects of routine late-season field operations on numbers of boll weevils (Coleoptera: Curculionidae) captured in large-capacity pheromone traps

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.     

Common subtropical and tropical nonpollen food sources of the boll weevil (Coleoptera: Curculionidae)

It is known that substantial boll weevil, Anthonomus grandis grandis Boheman, individuals can survive mild subtropical winters in some habitats, such as citrus orchards. Our study shows that endocarp of the fruit from prickly pear cactus, Opuntia engelmannii Salm-Dyck ex. Engel.; orange, Citrus sinensis L. Osbeck.; and grapefruit, Citrus paradisi Macfad., can sustain newly emerged adult boll weevils for >5 mo, which is the duration of the cotton-free season in the subtropical Lower Rio Grande Valley of Texas and other cotton-growing areas in the Western Hemisphere. Cotton, Gossypium hirsutum L., and the boll weevil occur in the same areas with one or all three plant species (or other citrus and Opuntia species that might also nourish boll weevils) from south Texas to Argentina. Although adult boll weevils did not produce eggs when fed exclusively on the endocarps of prickly pear, orange, or grapefruit, these plants make it possible for boll weevils to survive from one cotton growing season to the next, which could pose challenges to eradication efforts.     

Bacterial genera isolated from field-collected (Diapausing) and laboratory-reared cotton boll weevils, Anthonomus grandis (Coleoptera: Curculionidae)

Little data exist on the bacterial flora of the cotton boll weevil, Anthonomus grandis, which is a common insect pest to cotton farmers in the United States. This investigation determined the total numbers of aerobic and anaerobic bacteria in diapausing field-collected boll weevils and active adult laboratory-reared boll weevils. Identifications were made of aerobic genera isolated from field-collected and laboratory-reared boll weevils that had previously been surface sterilized. The genera found, in order of decreasing frequency, in the field-collected boll weevils were Lactobacillus, Erwinia, Flavobacterium, Enterobacter, and Pseudomonas. The genera found, in order of decreasing frequency, in the laboratory-reared boll weevils were Lactobacillus, Pseudomonas, Streptococcus, Erwinia, Enterobacter, and Flavobacterium, Lactobacillus was the most frequently found genus in both groups.     

Potential for transport of boll weevils (Coleoptera: Curculionidae) to the cotton gin within cotton modules

There is concern that cotton gins located in boll weevil, Anthonomus grandis grandis Boheman, eradication zones serving customers in adjacent infested zones may serve as a site for boll weevil reintroductions if weevils are transported alive inside cotton modules. We surveyed fields in three distinct areas of Texas and found that weevils can be present in large numbers in cotton fields that have been defoliated and desiccated in preparation for harvest, both as free adults and as immatures inside unopened bolls. Harvested cotton taken from module builders indicated that approximately = 100-3700 adult boll weevils were packed inside modules constructed at the sampled fields. Marked weevils were forced through a laboratory field cleaner (bur extractor) commonly mounted on stripper-harvesters, and 14% were recovered alive in the seed cotton fraction and lived at least to 24 h. Survival of weevils placed inside modules declined over time up to 7 d, but the magnitude of the decline varied with experimental conditions. In one experiment, 91% of the weevils survived to 7 d, whereas under harsher environmental conditions, only 11% survived that long. Together, our results indicate that when cotton is harvested in an infested area, boll weevils likely will be packed alive into cotton modules, and many will still be alive by the time the module is fed into the gin, at least up to 7 d after the module's construction.     

Boll weevil (Coleoptera: Curculionidae) survival through cotton gin trash fans

There is concern that cotton gins may serve as loci for reintroduction of boll weevils, Anthonomus grandis grandis Boheman, to eradicated or suppressed zones when processing weevil-infested cotton from neighboring zones. Previous work has shown that virtually all weevils entering the gin in the seed cotton will be removed before they reach the gin stand. Those not killed by the seed cotton cleaning machinery will be shunted alive into the trash fraction, which passes through a centrifugal trash fan before exiting the gin. The objective of this study was to determine survival potential of boll weevils passed through a trash fan. Marked adult weevils were distributed in gin trash and fed through a 82.6-cm (32.5-in.) diameter centrifugal fan operated across a range of fan-tip speeds. A small number of boll weevils were recovered alive immediately after passage through the fan, but all were severely injured and did not survive 24 h. In another experiment, green bolls infested with both adult- and larval-stage weevils were fed through the fan. Several teneral adults survived 24 h, and there was no evidence that fan-tip speed affected either initial survival of weevils, or the number of unbroken boll locks that could harbor an infesting weevil. Thus, designating a minimum fan-tip speed for ensuring complete kill is not possible for the boll weevil. Experiments suggest that a device installed in a gin that partially crushes or cracks bolls open before entering a trash fan will increase mortality, possibly enough that further precautions would be unnecessary.     

Genetic and phenotypic variation for flight ability in the cactophilicDrosophila species,D. aldrichi andD. buzzatii

The flight ability ofDrosophila aldrichi (Patterson & Crow) andD. buzzatii (Patterson & Wheeler) using tethered flights, was measured with respect to age-related changes, genetic variation and adult body size variation induced by rearing at different larval densities.Drosophila buzzatii flew for much longer thanD. aldrichi, especially females, but age-related changes in flight duration were significant only forD. aldrichi. Effects of body size on flight ability were significant inD. buzzatii, but not inD. aldrichi. InD. buzzatii, there was a significant genotype-environment interaction (larval density × line) for flight duration, with short and average flight duration isofemale lines showing longer flights, but a long flight duration line shorter flights as body size decreased (i.e., as larval density increased). Heritability estimates for flight duration were similar in the two species, but flight duration showed no significant genetic correlations with developmental time, body size or wing dimensions (except for one wing dimension inD. buzzatii). Although not significantly different between the species, heritabilities for life-history traits (adult size and developmental time) showed contrasting patterns — with higher heritability for body size (body weight and thorax length) inD. buzzatii, and higher for developmental time inD. aldrichi. In agreement with limited previous field evidence,D. buzzatii is better adapted for colonization than isD. aldrichi.     

Short-range dispersal and overwintering habitats of boll weevils (Coleoptera: Curculionidae) during and after harvest in the subtropics

Field experiments in the subtropical Lower Rio Grande Valley of Texas were conducted to determine the extent of adult boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), dispersal from cotton, Gossypium hirsutum L., fields during harvest operations and the noncotton-growing ("overwinter") period between 1 September and 1 February. Using unbaited large capacity boll weevil traps placed at intervals extending outward from commercial field edges, boll weevils did not move in substantial numbers during harvest much beyond 30 m, primarily in the direction of prevailing winds. From traps placed in fallow cotton; citrus; lake edge; pasture; treeline; sorghum, Sorghum bicolor (L.) Moench, and sugarcane, Saccharum spp., habitats during the overwinter period, the most boll weevils were collected in the fallow cotton fields and adjacent treelines during the fall. However, the greatest abundances of boll weevils were found in citrus orchards in the spring, before newly planted cotton fields began to square. One of the three lake edges also harbored substantial populations in the spring. Egg development in females was not detected between November and April, but in cotton fields most females were gravid between May and August when cotton fruiting bodies were available. Mated females, as determined by discoloration of the spermatheca, made up 80-100% of the female population during November and December but declined to approximately 50% in February. The lower incidence of mating indicates a reduction in physical activity, regardless of overwinter habitat, until percentages increased in March and April after cotton fields had been planted and squares were forming.     

Naturally-occurring biological control of the boll weevil [Col.: Curculionidae]

Red imported fire ants,Solenopsis invicta Buren, are effective predators of the boll weevil,Anthonomus grandis Boheman, in east Texas cotton fields. Boll weevils caused no economic loss in 11 years due to mortality attributed primarily to ants. Removal of the ants resulted in an increase in crop damage by the boll weevil. Insecticides used for cotton pests greatly reduce the abundance of the ants. To capitalize on this effective predation of boll weevils by ants, unnecessary applications of insecticides should be eliminated.     

Phagocytic and humoral immunity of the adult cotton boll weevil, Anthonomus grandis (Coleoptera: Curculionidae), to Serratia marcescens

This investigation determined phagocytic, lysozymal, and bactericidal defensive responses of adult laboratory-reared cotton boll weevils, Anthonomus grandis. Phagocytosis was first demonstrated in boll weevils at 3 hr following injection of live Serratia marcescens. Maximum phagocytosis was found in 16.4% of plasmatocytes at the end of 16 hr postinjection. Lysozyme activity was demonstrated in both inoculated and uninoculated boll weevils. Peak lysozyme activity of 6.9 μg/ml was found at 48 hr following inoculation of heat-killed Serratia marcescens. Bactericidal activity was demonstrated in inoculated boll weevils but not in uninoculated boll weevils. Peak bactericidal activity occurred at 24 hr following inoculation of heat-killed Serratia marcescens. Lysozymal and bactericidal activities were shown to be separate functions.     

Boll weevil (Coleoptera: Curculionidae) survival through the seed cotton cleaning process in the cotton gin

There is concern that gins located in boll weevil, Anthonomus grandis grandis Boheman, eradication zones may become points of reintroduction when they process cotton grown in a neighboring infested area. We estimated boll weevil survival through two typical machine sequences used in commercial cotton gins to clean and dry the seed cotton in advance of the gin stand, as well as separately through two incline cylinder cleaners or one or two tower dryers operating at different temperatures. Large numbers of laboratory-reared adult boll weevils were marked with fluorescent powder, fed into the test system, and recovered with the assistance of blacklights. We found no evidence of survival through the seed cotton cleaning systems even when the dryers were not heated, or when passed separately through the two incline cleaners alone. Upper confidence limits (95%) were calculated for the observed zero recoveries based on sample size and the binomial distribution, and these represent the statistical worst-case (i.e., highest) survival potential. Survival through heated tower dryers declined rapidly to zero at higher temperatures, especially when two dryers were running. Although we conclude that the potential for survival of weevils in the seed cotton to the gin stand is zero or close to zero, a small percentage of live weevils was recovered in the green boll/rock trap, which may represent the greatest threat of reintroduction at the gin. Escape of live weevils with the gin trash is also possible, and studies addressing this issue will be presented elsewhere.     

Suppression of Boll Weevil (Coleoptera: Curculionidae) Infestations on South Texas Cotton by Augmentative Releases of the Parasite Catolaccus grandis (Hymenoptera: Pteromalidae)

Augmentative releases of Catolaccus grandis (Burks) were conducted in a series of south Texas cotton fields during 1992 (April 30-June 29) in an attempt to suppress infestations of boll weevil, Anthonomus grandis Boheman. Within each of three release sites, the average incidence of mortality occurring among susceptible host stages (94.4-96.4% and 86.1-96.6% apparent mortality among third-stage larvae and pupae, respectively) was substantially greater than that occurring among these same stages in controls devoid of parasites (2.2-9.6% and 1.8-7.9% apparent mortality, respectively). Such differential mortality produced two important effects: (1) a significant reduction in densities of adult boll weevils produced in release sites relative to controls (0.0-0.1 and 0.3-1.6 unemerged adults/m², respectively), and (2) a concomitant reduction in the incidence of damaged bells during the postbloom period (0.2-0.4% and 48.3-91.7% in release and control sites, respectively). These results conclusively demonstrated the ability of C. grandis to 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 on cultivated cotton. The potential for augmentative biological control of boll weevil in the south Texas cotton environment is discussed.     

Survival of boll weevil （Coleoptera： Curculionidae） adults after feeding on pollens from various sources

The survival of overwintering boll weevil, Anthonomus grandis grandis （Boheman）, adults on non-cotton hosts in the Lower Rio Grande Valley （LRGV） of Texas was examined from 2001 to 2006. The success of the Boll Weevil Eradication Program, which was reintroduced into the LRGV in 2005, depends on controlling overwintering boll weevil populations. Laboratory studies were conducted using boll weevil adults that were captured in pheromone traps from September through March. The number of adults captured per trap declined significantly in the field from fall to the beginning of spring （3.5-7.0-fold）. The proportion of trapped males and females did not differ significantly. The mean weight of boll weevil adults captured in September was 13.3 mg, while those of captured adults from November to February were significantly lower and ranged from 6.7 to 7.8 mg. Our results show that boll weevil adults can feed on different plant pollens. The highest longevity occurred when adults were fed almond pollen or mixed pollens （72.6 days and 69.2 days, respectively） and the lowest when they fed on citrus pollen or a non-food source （9.7 days or 7.4 days, respectively）. The highest adult survival occurred on almond and mixed pollens [88.0%-97. 6% after 1st feeding period （10 days）, 78.0%-90.8% after 3rd feeding period （10 days）, 55. 0%-83.6% after 5th feeding period （10 days）, and 15.2%-32.4% after lOth feeding period （10 days）]. The lowest adult survival occurred on citrus pollen [52.0%-56.0% after 1st feeding period （10 days）, 13.3% after 3rd and 5th feeding periods （10 days）, and 0 after 6th feeding period （10 days）]. Pollen feeding is not a behavior restricted to adult boll weevils of a specific sex or physiological state. Understanding how boll weevil adults survive in the absence of cotton is important to ensure ultimate success of eradicating this pest in the subtropics.     

Forensic pollen geolocation techniques used to identify the origin of boll weevil re-infestation

The boll weevil, Anthonomus grandis, entered the United States of America in the early twentieth century and became a major pest in cotton, Gossypium spp. Shortly after the passage of Tropical Storm Erin on 16 August 2007 through the South Texas/Winter Garden boll weevil eradication zone, over 150 boll weevils were captured in the Southern Rolling Plains (SRP) eradication zone that was essentially weevil-free since 2003. Pollen analyses were made of the SRP weevils and weevils collected in two suspected source zones, Cameron (Southern Blacklands eradication zone) and Uvalde (Winter Garden eradication zone). An additional examination of the palynological evidence and examination of additional pollen residue shed new light on this event and strengthens the conclusion that the Uvalde area was the source of the SRP weevils. A total of 192 pollen grains from 39 taxa were found in the SRP weevils: 1904 pollen grains from ten taxa from the Cameron weevils and 148 grains from 28 taxa in the Uvalde weevils. The SRP weevils shared 16 taxa, including Phermeranthus sp. (flameflower) with the Uvalde weevils and only five taxa with the Cameron weevils. Common taxa between SRP and Uvalde weevils and the lack of the dominant ‘low spine’ Asteraceae that occurred in all Cameron samples confirm that the SRP weevils originated from the South Texas/Winter Garden zone. Problems associated with this type of research are similar to those in forensic palynology. These problems include the unknown origin of the weevils, pollen contamination and care and storage of the samples.     

Succinate-cytochrome c reductase activity and lipids in diapause and non-diapause Anthonomus grandis from different latitudes

Succinate-cytochrome c reductase (SCR) activity and fat content were compared for diapausing and non-diapausing boll weevils, Anthonomus grandis, collected from various latitudes. Thoracic mitochondrial SCR activity was unaffected by diapause; however, the SCR activity of abdominal mitochondria was reduced by 50% in diapausing weevils and the fat content increased by 2-fold. Diapausing weevils from the southernmost latitude showed the lowest SCR activity and the lowest fat content and were distinct from the other diapausing groups. No correlation was found between northern latitudes and SCR activity during diapause. The significance of the results is discussed from the standpoint of food quality and the evolution of diapause in the boll weevil.     

Potential for escape of live boll weevils (Coleoptera: Curculionidae) into cottonseed, motes, and cleaned lint at the cotton gin

Reintroductions of the boll weevil, Anthonomus grandis grandis Boheman, into areas of the United States where it has been eradicated or suppressed are very expensive to mitigate. There is concern that a cotton gin in an eradication zone may serve as a site of boll weevil reintroductions when processing cotton harvested in a neighboring infested zone. Similarly, there is a question whether weevil-free areas can safely import gin products, such as cottonseed and baled lint, from infested areas without risking an introduction. Many countries require fumigation of imported U.S. cotton bales to protect against boll weevil introductions, costing the U.S. cotton industry millions of dollars annually. In previously reported experiments, we quantified the potential for boll weevils to survive passage through precleaning machinery in the gin. In this study, we quantified survival potential of boll weevils passing through the gin stand and segregating into the cottonseed, mote, or lint fractions. We also examined boll weevil survival when passed with ginned lint through a lint cleaner. We present a flow chart of experimentally determined survival potentials of boll weevils passing through the various subprocesses of the gin, from which one can calculate the risk of a live boll weevil reaching any point in the process. Our data show that there is virtually no chance of a boll weevil being segregated alive into the cottonseed or of one surviving in the lint to approach the bale press. Therefore, quarantine or fumigation of cottonseed and cotton bales to guard against boll weevil introductions is unnecessary.     

Dispersal of boll weevils (Coleoptera: Curculionidae) from cotton modules before ginning

We characterized the level of risk of boll weevil, Anthonomus grandis grandis Boheman, reintroduction to an eradication zone posed by dispersal from cotton modules during and after transport to the gin. Mark-release-recapture experiments in August and September in Texas indicated that most weevils disperse rapidly from the module surface, temperature permitting, unless confined under a module tarp, where most died. Nevertheless, 1-5% of released weevils were recovered alive after 24 h on the side and top surfaces of modules, representing potential dispersants. Mortality of boll weevils caged on the top surface of a module was 95-100% after 1-4 d when maximum air temperatures were > or = 33 degrees C and 72-100% when minimum temperatures were -7 degrees C or lower, but a few survived even after experiencing a minimum daily temperature of -12 degrees C. Under warm (daily maximum temperatures > or = 25 degrees C) and cold (daily minimum temperatures < or = 0 degrees C) weather conditions, survival was higher under the tarp than on the open surface of the module (20 versus 7% and 42 versus 26%, respectively), but mortality was 100% in both locations when temperatures reached 34 degrees C. Our results indicate that although the threat to an eradication zone posed by boll weevil dispersal from an infested module is very low under most environmental conditions, it is probably greatest when 1) a module is constructed and transported from an infested zone during weather too cool for flight, followed by warm weather favorable for flight at the gin yard; or 2) such a module is transported immediately after construction in moderate-to-warm weather.     

Cholesterol oxidase: an oöstatic and larvicidal agent active against the cotton boll weevil,Anthonomus grandis

The enzyme cholesterol oxidase (E.C. 1.1.3.6), purified from Streptomyces culture filtrate was previously found to have oral insecticidal activity on neonate larvae of the boll weevil (Anthonomus grandis grandis Boheman) from a laboratory population. In the present study, second instar larvae were also controlled by the enzyme at diet concentrations similar to those which control neonates (12 day LC₅₀ = 2.4 μg.ml^?1 in diet). Larvae from field-collected adults were similarly susceptible to cholesterol oxidase in the diet. When ingested by adult females during the mating/pre-oviposition period, cholesterol oxidase greatly reduced subsequent oviposition (83% reduction in eggs laid as compared to controls) and larval survival (97% reduction from controls). Dissection of treated adult females revealed poorly developed ovaries and few developing oöcytes. These studies were conducted to further evaluate the utility of cholesterol oxidase in a program to establish boll weevil-resistant transgenic cotton.     

Effects of burial and soil condition on postharvest mortality of boll Weevils (Coleoptera: Curculionidae) in fallen cotton fruit

Effects of soil condition and burial on boll weevil, Anthonomus grandis grandis Boheman, mortality in fallen cotton, Gossypium hirsutum L., fruit were assessed in this study. During hot weather immediately after summer harvest operations in the Lower Rio Grande Valley of Texas, burial of infested fruit in conventionally tilled field plots permitted significantly greater survival of weevils than in no-tillage plots. Burial of infested squares protected developing weevils from heat and desiccation that cause high mortality on the soil surface during and after harvest in midsummer and late summer. A laboratory assay showed that burial of infested squares resulted in significantly greater weevil mortality in wet than in dry sandy or clay soils. Significantly fewer weevils rose to the soil surface after burial of infested bolls during winter compared with bolls set on the soil surface, a likely result of wetting by winter rainfall. A combination of leaving infested fruit exposed to heat before the onset of cooler winter temperatures and burial by tillage when temperatures begin to cool might be an important tactic for reducing populations of boll weevils that overwinter in cotton fields.