In 1997, Jarzynski proved a remarkable equality that allows one to compute the equilibrium free-energy difference ⌬F between two states from the probability distribution of the nonequilibrium work W done on the system to switch between the states, e ؊⌬F͞kT ‫؍‬ ͗e ؊W͞kT ͘, [Jarzynski, C. (1997) Phys. Rev. Lett. 87, 2690 -2693]. The Jarzynski equality provides a powerful free-energy difference estimator from a set of N irreversible experiments and is closely related to free-energy perturbation, a common computational technique for estimating free-energy differences. Despite the many applications of the Jarzynski estimator, its behavior is only poorly understood. In this article we derive the large N limit for the Jarzynski estimator bias, variance, and mean square error that is correct for arbitrary perturbations. We then analyze the properties of the Jarzynski estimator for all N when the probability distribution of work values is Gaussian, as occurs, for example, in the near-equilibrium regime. This allows us to quantitatively compare it to two other free-energy difference estimators: the mean work estimator and the fluctuation-dissipation theorem estimator. We show that, for near-equilibrium switching, the Jarzynski estimator is always superior to the mean work estimator and is even superior to the fluctuation-dissipation estimator for small N. The Jarzynski-estimator bias is shown to be the dominant source of error in many cases. Our expression for the bias is used to develop a bias-corrected Jarzynski free-energy difference estimator in the nearequilibrium regime.A ccurate measurement and calculation of free-energy differences is central to our understanding of biological, chemical, and physical molecular processes. A common method of estimating the free-energy difference ⌬F ϭ F B Ϫ F A between two states, A and B, of a classical system in contact with a heat reservoir is to perturb the system to induce a transition between these states. The average work done in such a perturbation satisfies ͗W͘ Ն ⌬F, where equality holds if and only if the perturbation is infinitely slow. An average of the work values obtained by any finite time experiment or simulation therefore overestimates the true ⌬F. Until recently, recovering the equilibrium free energy from trajectories arbitrarily far from equilibrium was therefore thought to be impossible.In 1997, however, Jarzynski (1, 2) proved an identity that relates the probability distribution of nonequilibrium work values with the equilibrium free-energy difference between the two states:where ␤ ϭ (kT) Ϫ1 . On the left-hand side of this equation is an exponential of the equilibrium free-energy difference, and the right-hand side is an exponentially weighted average over an infinite number of nonequilibrium work trajectories, all started from the same initial equilibrium state. Although the second law of thermodynamics requires that the average work over all possible trajectories be greater than the free-energy difference, the work for an individual trajectory will occasional...

Genetically modified cotton, Gossypium hirsutum L., cultivars ('Bollgard') that produce crystalline proteins from Bacillus thuringiensis (Berliner) are valuable tools for managing lepidopteran insect pests in the United States. However, high numbers of bollworm, Helicoverpa zea (Boddie), larvae have been observed feeding in white flowers of these cultivars. Fresh tissue bioassays were conducted to investigate bollworm survival on Bollgard and 'Bollgard II' cottons. Bollworm survival was higher on square and flower anthers than on other floral structures on 'Deltapine 5415' (conventional cotton) and 'NuCOTN 33B' (Bollgard). Bollworm survival at 72 h was higher on all floral structures from Deltapine 5415 than on corresponding structures from NuCOTN 33B. ELISA tests indicated that CryIA(c) expression varied among plant parts; however, bollworm survival did not correlate with protein expression levels. Trends in bollworm survival on Bollgard II were similar to those on Bollgard and conventional cotton; however, survival was lower on all structures of Bollgard II than on corresponding structures of Bollgard and conventional cotton. These data support field observations of bollworm injury to white flowers and small bolls and provide a better understanding of larval behavior on Bollgard cotton.

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Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), infestations in most of North America north of Mexico arise from annual migrations of populations that overwinter in southern Texas and Florida. A comparison of the cytochrome oxidase I haplotype profiles within the fall armyworm corn-strain, the subgroup that preferentially infests corn (Zea mays L.) and sorghum (Sorghum vulgare Pers.), identified significant differences in the proportions of certain haplotypes between the Texas and Florida populations. These proportional differences were preserved as the populations migrated, providing a molecular metric by which the source of a migrant population could be identified. The migratory pattern derived from this method for several southeastern states was shown to be consistent with predictions based on analysis of historical agricultural and fall armyworm infestation data. These results demonstrate the utility of haplotype proportions to monitor fall armyworm migration, and they also introduce a potential method to predict the severity of cotton crop infestations in the short term.

The primary management tactic for lepidopteran pests of cotton in the United States of America (USA) is the use of transgenic cotton that produces Bacillus thuringiensis Berliner (Bt) toxins. The primary target pests of this technology are Helicoverpa zea (Boddie) and Heliothis virescens (F.) in the eastern and central Cotton Belt of the USA. Concerns over the evolution of resistance in H. zea to Bt toxins and scrutiny of the necessity of Bt crops has escalated. We reviewed published and unpublished data from field trials of Bt cotton in the eastern and central Cotton Belt of the USA through 2015 to evaluate the effectiveness of Bt cotton (Bollgard, Bollgard II, WideStrike, WideStrike 3, and TwinLink). Bt cotton reduced insecticide usage, reduced heliothine pest numbers and damage, and provided a yield benefit, but Bollgard II and WideStrike efficacy declined in the Midsouth over the period evaluated. In the Southeastern region, heliothine damage remained constant through 2015, but yield benefits declined from 2010 until 2015. Resistance of H. zea to several Bt toxins is the most plausible explanation for the observed changes in Bt cotton efficacy. The introduction of new Bt toxins such as found in Widestrike 3 and Twinlink may preserve the benefits of Bt crops. However, while both Widestrike 3 and Twinlink had less damage than Widestrike, damage levels of both were similar to Bollgard II.

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is a major pest of citrus crops worldwide. A large number of insecticides have been used to manage D. citri in Florida. Therefore, insecticide resistance could become an important problem facing citrus production. Monitoring insecticide susceptibility in populations of D. citri and providing a technique to use as an early warning is needed so citrus producers can modify chemical control strategies for this pest in Florida. The objective of this study was to develop a simple and fast tool to determine insecticide resistance in D. citri and apply it to commercial citrus production in Florida. LC50 and LC95 estimates were determined for 8 commonly used insecticides on a susceptible laboratory population of D. citri 24 h after treatment in a residual contact bottle assay. Five to 7 concentrations of each insecticide were tested. The LC50 values (and 95% fiducial limits) ranged from 0.06 (0.02-0.26) to 0.80 (0.26-2.46) ng/µL for each insecticide tested. Exposure time-mortality indices were determined for 0, 10, 100, 1,000, and 10,000 ng/µL concentrations of each insecticide in a laboratory susceptible strain. Knockdown was assessed after 15, 30, 45, 60, 75, 90, 105, and 120 min. Complete knockdown (100.0%) occurred within 60 min for dimethoate, fenpropathrin, imidacloprid, bifenthrin, and flupyradifurone at the 10,000 ng/µL concentration. For spinetoram, 86.7% knockdown occurred within 120 min at 10,000 ng/µL. For sulfoxaflor and cyantraniliprole, 44.0 and 42.6% knockdown, respectively, occurred within 120 min at 1,000 ng/µL. We also developed a bottle bioassay to survey field populations of D. citri for insecticide resistance in central Florida. Exposure time-mortality indices developed in the laboratory were used to assess susceptibility of 1 laboratory and 4 field populations of D. citri after 15, 30, 50, 75, 90, 105, and 120 min of exposure at the 10,000 ng/μL concentration of various insecticides. Little to no evidence of resistance was detected for bifenthrin, dimethoate, imidacloprid, and fenpropathrin in central Florida. Our investigation demonstrated that a bottle bioassay is suitable for assaying insecticide resistance in D. citri adults under laboratory and field conditions. It should be a flexible tool for rapid testing of insecticide resistance in possible cases of insecticide failure. Its simplicity should allow trained professionals to rapidly monitor for insecticide resistance in commercial settings where "hot spots" of D. citri populations may occur.