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Transgenic Bt-cotton now dominates the cotton-growing belt in northwestern China where there are few natural plant refuges to act as sources of moths susceptible to Bt toxin. As an initial step towards developing an insect resistance management (IRM) plan for the pest moth, Helicoverpa armigera, on Bt-cotton in this part of China, we assessed the potential of six crops grown in two configurations to act as refuge hosts for susceptible moth production in both broad-acre and small-holder farms. Egg and larval abundance indicated that H. armigera had a preference for chickpea, pigeon pea, and corn, over cotton, sorghum, and benne (sesame). There were no significant differences in egg or larval abundance between plot and strip configurations of these crop hosts. We found that sorghum was not attractive to H. armigera, contrary to the findings in other cotton production areas. Moreover, chickpea, pigeon pea, and corn were determined to be potential refuge hosts based on egg and larval abundance over the growing season. From the adult moth population dynamics in broad-acre and small-holder farms, the efficiency of alternative refuge crops, and local agricultural practices, we recommend that spring corn be grown as a strip crop as part of an IRM strategy to improve the probability of Bt-susceptible moth production and mating with resistant moths in broad-acre farms. In small-holder farms where current agricultural practices are entrenched, wheat and summer corn should be evaluated as refuge crops in the future. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the relationship between fertilization and the incidence of insect pests is essential for the management of chemical fertilization and insect pests in modern agroecosystem. In this paper, effects of potassium supply alone and combination of nitrogen and potassium fertilizers on population dynamics and density of cotton aphid Aphis gossypii (Hemiptera: Aphididae) were investigated during seedling stage in Bacillus thuringiensis (Bt)-cotton production system. The results showed that high concentration of potassium fertilizer significantly reduced cotton aphid population density when nitrogen fertilizer was not used. Aphid population dynamics and density at peak time were obviously affected by the combination of nitrogen and potassium fertilizers in different rate, whereas different population dynamics of aphid were showed among different treatments. Compared with potassium fertilizer used alone, the same or significantly reduced aphid densities were observed in combination treatments of 120kg/ha potassium with 108kg/ha and 144kg/ha nitrogen levels in both years. In addition, cotton aphid population density was significantly affected by interaction of nitrogen and potassium fertilizers in field experiments of two years, these results indicated that cotton aphid population density at seedling stage was suppressed by potassium fertilizer and the combination of potassium and nitrogen fertilizers in proper rate (K:N=1:0.9 or 1:1.2kg/ha). Suggesting that proper application of potassium and nitrogen fertilizers should be beneficial to controlling insect herbivores such as cotton aphid and plant growth at seedling stage of Bt-cotton field in Central China. [Copyright &y& Elsevier]

China was the first developing country to introduce Bt cotton on a large scale. This paper provides an in-depth economic analysis of Bt cotton production by small-scale farmers in China. Data were collected in 2002 in Linqing County, in Shandong Province and comprised a season-long cotton production monitoring with 150 farmers and complementary household interviews. For quality assessment, the Bt toxin concentration of the various Bt varieties used by the farmers was determined for each plot. All farmers were growing insect resistant Bt cotton varieties. Yet, they sprayed high amounts of chemical insecticides, out of which 40% were extremely or highly hazardous. The paper reviews methodological issues inherent to impact assessment of crop biotechnology and identifies market and institutional failure as possible reasons for continued high pesticide use. Using the damage function methodology the coefficients for both damage control inputs, i.e., Bt varieties (measured as toxin concentration), and insecticide quantity were not significantly different from zero. Results show that absence of enabling institutions and lack of farmer knowledge can considerably limit the benefits of Bt cotton for small-scale farmers. The paper points out the importance to include the institutional conditions in the evaluation of agricultural biotechnology in developing countries. [ABSTRACT FROM AUTHOR]

Bt-cotton seed has been effective to control the damage of bollworm in Chinese cotton production since 1999, reducing the need for pesticides and increasing incomes of Chinese farmers. Field data collected in 2004 indicates that these benefits have been eroded by increasing the use of pesticides aimed to control secondary pests. The combination of Bt-cotton seed and other forms of biological pest control may help farmers regain the economic and environmental benefits of previous years. Failure to find a solution, may lead to the discontinuation of the use of Bt-cotton seed in China and elsewhere. [ABSTRACT FROM AUTHOR]