Bollgard cotton is the trademark given to a number of varieties of cotton bio-engineered to produce an insecticidal protein from Bacillus thuringiensis (Bt). When produced by the modified cotton plants, this protein controls certain lepidopterous cotton insect pests. Commercially available since 1996, these cotton varieties are purchased under a license agreement in which the growers pay a fee and agree to abide by the terms, which include a 1-year license to use the technology and agreement to participate in an insect resistance management program. Today, Bollgard cotton is grown on more than one-third of all cotton acreage in the USA. This product has reduced cotton production costs and insecticide use by providing an effective alternative to chemical insecticides for the control of tobacco budworm, Heliothis virescens; cotton bollworm, Helicoverpa zea; and pink bollworm, Pectinophora gossypiella. The specificity and safety profile of the Bt protein produced in planta in cotton was maintained. It has retained its selectivity for lepidopterous insects and lacks the characteristics found in potential allergenic proteins. Fiber quality, the agronomic characteristics of the plant and seed composition remain unchanged. New cotton technology is being developed to provide improved insect control and a wider spectrum of activity. These future products could further reduce insecticide use in the production of cotton, while maintaining the high level of safety and reliability that has been demonstrated by five seasons of Bollgard cotton use.
Cereal leaf beetle, Oulema melanopus (L.), has become a serious pest of small grains in the mid-Atlantic region of the United States. Existing thresholds for implementing control measures allowed too much leaf damage and consequent yield loss to occur before recommending treatment. Information on beetle biology and crop response to injury, both prerequisites for developing new management strategies, was lacking for this region. A 3-yr project was initiated to generate an area wide cereal leaf beetle biological and yield impact database for winter wheat, and to evaluate the injury and yield loss potential of different population densities. Over the study period, beetle populations were evaluated at 26 winter wheat field locations in Virginia and North Carolina. Eggs and larvae, classified to instar, were counted twice each week from February to June. Replicated insecticide versus noninsecticide treatments were conducted at each location where leaf defoliation and yield were documented. Results showed that the relationship between 50th percentile egg and fourth-instar population estimates were in strong agreement (y = 0.36x - 0.01; r2 = 0.79). Potentially detrimental larval infestations were forecast before appearance of foliage injury from egg populations present during the stem elongation to flag leaf emergence developmental stages. A significant positive linear relationship between total fourth instar per stem population estimates and percent flag leaf defoliation was detected (y = 20.29x + 1.34; r2 = 0.60). A weaker but still significant relationship between the total fourth-instar population estimates and percent yield loss was found (y = 11.74x + 6.51; r2 = 0.26), indicating that factors in addition to flag leaf injury, primarily by fourth instars, also contributed to reduced yields.
Three techniques for estimating wheat foliage defoliation by cereal leaf beetle, Oulema melanopus (L.), larvae were evaluated. The techniques were visual estimation, computer estimation with image capture through a flatbed scanner (Lanalyze), and a commercially available video computer image analysis system (CIAS). Both computer-assisted techniques exhibited high levels of repeatability. Both consistently produced errors of less than 3 percent, although each system exhibited different error patterns. The Lanalyze system tended to systematically underestimate actual defoliation of mock leaves, while the CIAS system tended to overestimate actual defoliation. Visual estimators exhibited greater variation among estimates and, on average, greater discrepancies from actual defoliation when compared with the computer assisted techniques. The experience of the observer had a bearing on the accuracy and consistency of visual estimates; more experienced observers had the best accuracy.
Field experiments were conducted in the spring of 1994 at the V. G. James Research and Extension Center in Plymouth, NC and 1995 at the Gaylon Ambrose farm near Washington, NC. A RCB test design was employed each season. Plots in each year were 6.0 ft X 50.0 ft with 6.0 ft alleyways between plots. Insecticide applications were made on 21 Apr 1994 and 28 Apr 1995. Treatments were applied by a CO, powered backpack sprayer equipped with three hollow cone Tee Jet® X-8 nozzles spaced 1.5 ft apart. The sprayer delivered 14.9 gpa at 44.0 psi which provided an effective spray swath of 4.5 ft when operated at 2.0 ft above the canopy. Treatments were evaluated four days after application by taking 25 and 15 sweeps from each plot in 1994 and 1995, respectively. The sweep net had a standard 1.0-inch.
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