Transfer of CrylAc and Cry2Ab proteins from genetically engineered Bt cotton to herbivores and predators

With the cukivation of Bt cotton, the produced insecticidal Cry proteins are ingested by herbivores and potentially transferred along the food chain to natural enemies, such as predators. In laboratory experiments with Bollgard II cotton, concentrations of CrylAc and Cry2Ab were measured in Lepidoptera larvae （Spodoptera littoralis, Hello- this virescens）, plant bugs （Euschistus heros）, aphids （Aphis gossypii）, whiteflies （Bemisia tabaci）, thrips （ Thrips tabaci, Frankliniella occidentalis）, and spider mites （Tetranychus urticae）. Tritrophic experiments were conducted with caterpillars ofS. littoralis as prey and larvae of ladybird beetles （Harmonia axyridis, Adalia bipunctata） and lacewings （Chrysop- erla carnea） as predators. Immunological measurements （ELISA） indicated that herbivores feeding on Bt cotton contained 5%-50% of the Bt protein concentrations in leaves except whiteflies and aphids, which contained no or only traces of Bt protein, and spider mites, which contained 7 times more Cry 1Ac than leaves. Similarly, predators contained 1%-30% of the Cry protein concentration in prey. For the nontarget risk assessment, this indicates that Bt protein concentrations decrease considerably from one trophic level to the next in the food web, except for spider mites that contain Bt protein concentrations higher than those measured in the leaves. Exposure of phloem sucking hemipterans is negligible.

A simple and easy method to measure ammonia volatilization:Accuracy under field conditions

Field studies on soil ammonia(NH_(3))volatilization are restricted in many countries owing to the high costs commonly demanded for accurate quantification.We assessed the accuracy of a simple,open chamber design to capture NH_(3)under field conditions,as affected by different chamber placement schemes.Urea-15 N was surface applied to lysimeters installed in the spaces between maize rows.Open chambers made from plastic bottles were installed on each lysimeter with variations in i)N rates(3,8,13,and 18 g m^(-2)),ii)the height of the chamber above the soil surface(0,5,and 10 mm),and iii)chamber relocation(static vs.dynamic).Reference lysimeters without chambers were used to measure NH_(3)losses by^(15)N-balance.Losses of NH_(3)-N accounted for more than 50%of the applied N.Relocation of the chambers had no impact on their NH_(3)-trapping efficiencies,proving to be an unnecessary procedure.Variation in the height of the chambers above the soil surface affected the capture of NH_(3),but the results still maintained high linearity with the NH_(3)losses quantified by the reference method(R^(2)>0.98).When the same placement scheme used in the introductory study describing the chamber was utilized(static and touching the soil surface),we found a trapping efficiency of 60%,which was very similar to that(57%)obtained in the previous study.Our results show that this simple,open chamber design can be used with satisfactory accuracy under field conditions,provided that simple,standardized procedures are warranted.

Optimizing the use of open chambers to measure ammonia volatilization in field plots amended with urea

Measuring ammonia(NH_(3))volatilization from urea-fertilized soils is crucial for evaluation of practices that reduce gaseous nitrogen(N)losses in agriculture.The small area of chambers used for NH_(3)volatilization measurements compared with the size of field plots may cause significant errors if inadequate sampling strategies are adopted.Our aims were:i)to investigate the effect of using multiple open chambers on the variability in the measurement of NH_(3)volatilization in urea-amended field plots and ii)to define the critical period of NH_(3)-N losses during which the concentration of sampling effort is capable of reducing uncertainty.The use of only one chamber covering 0.015%of the plot(51.84 m^(2))generates a value of NH_(3)-N loss within an expected margin of error of 30%around the true mean.To reduce the error margin by half(15%),3–7 chambers were required with a mean of 5 chambers per plot.Concentrating the sampling efforts in the first two weeks after urea application,which is usually the most critical period of N losses and associated errors,represents an efficient strategy to lessen uncertainty in the measurements of NH_(3)volatilization.This strategy enhances the power of detection of NH_(3)-N loss abatement in field experiments using chambers.

Reduced Mythimna separata infestation on Bt corn could benefit aphids

Use of genetically engineered plants that express insecticidal Cry proteins derived from Bacillus thuringiensis(Bt)have been proven efficacious for managing lepidopteran pests.However,in some cases herbivores that are not targeted by the Bt trait have increased in importance.It has been suggested that reduced caterpillar damage to Bt crops could lead to decreased levels of induced plant defensive compounds which might benefit other non-target herbivores.Here we investigated the potential effect of reduced damage by larvae of Mythimna separata on aphid populations in Bt corn.We compared the performance of Rhopalosiphum maidis feeding on non-Bt corn plants that had been infested by M.separata larvae or were uninfested.The results showed that caterpillar-infested corn plants significantly reduced the fitness of R.maidis leading to a prolonged nymphal development time,reduced adult longevity and fecundity compared to uninfested plants.Consequently,the population growth rate of corn aphids feeding on caterpillar-infested corn plants was significantly lower than on uninfested plants.As expected,the aphids performed significantly better on Lepidoptera-resistant Bt corn than on non-Bt corn when plants were infested with M.separata,since the caterpillars caused very little damage to the Bt plants.The current findings indicate that reduced M.separata infestation could benefit aphid development in Bt corn.Bt corn has the potential to be commercialized in China in the near future and aphids and other non-target pests should be monitored in the farming fields.