22 research outputs found
Novel Pink Bollworm Resistance to the Bt Toxin Cry 1Ac: Effects on Mating, Oviposition, Larval Development and Survival
Bt cotton plants are genetically engineered to produce insecticidal toxins from the Bacillus thuringiensis (Bt) Berliner (Bacillales: Bacillaceae) bacterium and target key lepidopteran pests. In all previous strains of pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) selected in the laboratory for resistance to insecticidal Cry1Ac toxin using an artificial diet containing the toxin, resistance to Cry1Ac and to Bt cotton is linked to three cadherin alleles (r1, r2, and r3). In contrast, the BG(4) pink bollworm strain was selected for resistance to Bt cotton by feeding larvae for four days in each of 42 generations on bolls of ‘NuCOTN33B®’ that expressed Cry1Ac toxin. After additional selection for eleven generations on Cry1Ac-incorporated diet, the susceptibility to Cry1Ac, fecundity, egg viability, and mating of this strain (Bt4R) was compared with the unselected Cry1Ac-susceptible parent strain. Some larvae of the Bt4R strain survived on diet containing ≥ 10 µg Cry1Ac per milliliter artificial diet, but none survived on transgenic cotton bolls. In contrast to strains selected exclusively on Cry1Ac diet, some survival of progeny of reciprocal moth crosses of Bt4R resistant and Bt-susceptible strains occurred on Cry1Ac-treated diet, suggesting differences in levels of dominance. The Bt4R resistant strain does not have the r1, r2, or r3 mutant cadherin genes as do all previous strains of pink bollworm selected on Cry1Ac-treated artificial diet. The combined results suggest a mechanism of resistance to Cry1Ac that is different from previously described cadherin mutations
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Cotton Aphid Biology and Honydew Production
Cotton aphid, Aphis gossypii Glover, fecundity, nymph development and honeydew production were studied in the laboratory. Apterous adult females produced an average of 1.7 nymphs per day and the nymphs (four instars) developed to adults in an average of 4.1 days at 26.7° C in the laboratory. Average longevity of adults was 16.1 days. More honeydew drops were produced by one-day old nymphs than three- or four-day old nymphs. Numbers of honeydew drops produced on a day to day basis were highly variable and did not show a distinct pattern of production. More honeydew drops, sugars and progeny were produced by adults at 26.7° C compared with 15.6 or 32.2° C. Increasing times of exposure of clean cotton lint to aphids and the resulting increasing amounts of honeydew sugars under laboratory and field conditions were significantly related to increasing cotton lint stickiness as measured with a thermodetector
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Pink Bollworm: Diapause Larval Exit from Harvested Immature Cotton Bolls and Percentages Surviving to Moth Emergence
Pink bollworm (PBW), Pectinophora gossypiella (Saunders), diapause larval exit from immature green bolls and larval and pupal mortality after exiting bolls, were studied at Phoenix, AZ in the insectary. Diapause larvae exited immature bolls sporadically during January, February, and early March. Thereafter, exit from the bolls was more consistent and highest numbers emerged in late April, May or early June. Larval and pupal mortality were high during January to early February and March, decreased in mid-March through early June, and increased again in mid-June to early August. Larvae remained in immature bolls as long as 319 days after harvest. Moth emergence was significantly correlated to accumulated heat units (12.8 and 30.6°C lower and upper developmental thresholds)
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Preliminary Screening of Different Cottons for Resistance to Sweetpotato Whitefly Infestations
Cotton, Gossypium spp., varying in leaf color (green vs. red), leaf shape (normal vs. okra) and leaf hairs per cm2 of leaf area were evaluated for sweetpotato whitefly (SPW), Bemisia tabaci (Gennadius) Biotype B preference. Regression analysis showed SPW adults, eggs and nymphs were significantly related to leaf hairiness. Seasonal mean numbers of SPW adults, eggs, and nymphs were high variable within and between leaf color, shape, and hairiness types. Further studies are justified since some of the cottons may be potential sources of SPW resistant germplasm
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Seasonal Distribution of Bemesia Honeydew Sugars on Pima and Upland Cotton Lint
Bemisia argentifolii Bellows and Perring populations were higher on Pima S-7 cotton compared with DPL 50 cotton. Higher numbers of mature open cotton bolls occurred earlier for DPL 50 compared with Pima S-7. Also, numbers of open bolls for DPL 50 peaked 8 to 14 days before Pima S-7 and decreased dramatically by 15 September reflecting termination of the first fruiting cycle in August In contrast the indeterminate fruiting pattern of Pima S-7 showed that numbers of open bolls per week declined gradually after the peak without a clear cut termination occurrence. About 95 and 80% of the open cotton bolls, of the Deltapine and Pima S-7 cottons, respectively, occurred by mid- September. This suggests that defoliation timing and early harvest can be important management tools to avoid sticky cotton. For upland cotton, extending the cotton season after 95% of the crop matured (≅ 15 September) resulted in development from non - sticky cotton to lightly- sticky cotton within 21 days following the occurrence of increasing whitefly populations after 15 September. Later fruiting and lack of a distinct end of the first cotton fruiting cycle probably precludes using early defoliation for long -staple Pima cotton. At harvest, thermodetector counts for all weekly harvests were greater than amounts found in lint for randomly selected 20 boll samples; and samples from all cotton picked from 4 m of row. This probably occurred because weekly picked cotton escaped rainfall and exposure and other weathering, in 1995 but not 1996, and machine - picked cotton contains more honeydew- contaminated leaf trash. Except in one instance, thermodetector counts and trehalulose and melezitose content in lint for all sampling methods were significantly correlated
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Effects of Entomopathogentic Nematodes on Pink Bollworm Mortality
Steinernema riobravis Cabanillas, Poinar & Raulston infected pink bollworm Pectinophora gossypiella (Saunders), larvae over a temperature range of 15.6 - 38.0° C. Temperatures of 32.2° C and higher and exposure for 48 h or more often resulted in decreased numbers of nematode killed larvae with living nematodes and increased numbers of dead larvae with dead or no nematodes
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Pink Bollworms in 'Detapine 90' and 'Pima S-6' Cottons in Arizona
Pink bollworm (PBW), Pectinophora gossypiella (Saunders) infestations in Deltapine 90, Gossypium hirsutum L., and Pirna S-6, G. barbadense L., cotton bolls were initiated at about the same time during the cotton growing season. Male moth trap catches in gossyplure-baited Delta traps followed similar trends in both cottons throughout the season, but tended to be higher in Pima S-6 cotton than in Deltapine 90 cotton late in the season. Late crop termination (last irrigation 26 September) as practiced in Pima cotton production vs. earlier crop termination (last irrigation I September) as practiced in upland cotton production resulted in higher numbers of late- season immature green bolls, higher numbers of PBW larvae per boll and higher populations of diapause larvae at harvest time in Pima than occurred in the upland cotton cultivar. PBW seed damage was lower in the Deltapine 90 cultivar than in the Pima S-6 cotton cultivar. Deltapine 90 lint yield was higher than Pima S-6 lint yield
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Steinernematid Nematode Infections of Pink Bollworm Larvae in Field Tests
Under field conditions, pink bollworm (PBW), Pectinophora gossvpiella (Saunders), larvae were exposed to soil samples from plots treated with Steinernema riobravis at the rate of 5 nematodes per cm² of soil surface. Larval mortalities were 50% on the day of treatment and 2.5% on day 90 following treatment with irrigations about every 14 to 21 days,. Larval mortality percentages after exposure to soil samples from plots treated with S. carpocapsae at the rate of 5 per cm2 of soil surface were 32.5, 15.3, 5.3 and 2.5 for the day of treatment and day 1, 7, and 15 following treatment, respectively. No further mortality occurred in bioassays conducted up to 90 days following treatment. With plots treated with 25 nematodes per cm² of soil surface, PBW larval mortalities ranged from 100% on the day of treatment to 7.5% on day 63 following treatment with S. riobravis and 92.5% on the day of treatment to 5% on day 7 following treatment with S. carpocapsae. Percentages of larval mortality after exposure to soil samples from plots treated with S. riobravis increased after each irrigation, but did not increase after exposure to soil samples from plots treated with S. carpocapsae
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Cabbage Looper, Tobacco Budworm, and Beet Armyworm Larval Mortalities, Development and Foliage Consumption on Bt and Non-Bt Cottons
Tobacco budworm (TBW), Heliothis virescens (F.), larvae were highly susceptible to feeding on Bt cotton leaves or flower buds with 100% and 96% mortality occurring within 4 days, respectively, compared to an average mortality of 95% for cabbage looper (CL), Trichoplusia ni (Hübner), and 57% for beet armyworm (BAW), Spodoptera exigua (Hübner), after 14 days feeding on Bt leaves. Larval weights, of CL and BAW after 7, 10, or 14 days of feeding on Bt leaves were lower compared with those feeding on non-Bt cotton leaves. BAW, CL, and TBW larvae consumed significantly less Bt leaf area per feeding day compared with DPL 5415
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Effects of Aqueous Sprays of Silverleaf Whitefly Honeydew Sugars on Cotton Lint Stickiness
Sprays of commercially-procured sugars that are also found in silverleaf whitefly Bemisia argentifolii Bellows and Perring [= B. tabaci (Gennadius) Strain B] honeydew were applied to clean cotton lint to determine the relationship between the sugars and cotton lint stickiness. Increasing concentrations of the sugars resulted in increasing thermodetector counts