A RAPD-PCR-based genetic diversity analysis of Helicoverpa armigera and H. zea populations in Brazil.

Helicoverpa armigera is the most significant pest of agriculture in Asia, Europe, Africa, and Australasia, causing damage to crops greater than US$2 billion annually and until 2013 it was not detected in Brazil. Helicoverpa zea is restricted to the American continent and is important to corn and a secondary pest of cotton and tomatoes. The wide range of crops exploited by H. armigera (mainly cotton, soybeans, chickpea, and corn), the possible mating between these species can promote population shifts, that could be assessed by RAPD-PCR technique. Therefore, the aim of this study was to determine the genetic diversity of H. armigera and H. zea populations by RAPD-PCR analysis. The most important result was the clustering of one H. armigera population in a group predominantly formed by H. zea. It could indicate a possible occurrence of an interspecific cross between these species. This is a concern to Brazilian agriculture due to the possibility of selection of hybrids well adapted to the American environment, which would be inherited from H. zea. The other noxious fact is the possible development of new biotypes resistant to insectides or Bt toxins expressed in transgenic crops, came from H. armigera gene pool.

Economic injury level for the coffee berry borer (Coleoptera: Curculionidae: Scolytinae) using attractive traps in Brazilian coffee fields.

The currently existing sample procedures available for decision-making regarding the control of the coffee berry borer Hypothenemus hampei (Ferrari) (Coleoptera: Curculionidae: Scolytinae) are time-consuming, expensive, and difficult to perform, compromising their adoption. In addition, the damage functions incorporated in such decision levels only consider the quantitative losses, while dismissing the qualitative losses. Traps containing ethanol, methanol, and benzaldehyde may allow cheap and easy decision-making. Our objective was to determine the economic injury level (EIL) for the adults of the coffee berry borer by using attractant-baited traps. We considered both qualitative and quantitative losses caused by the coffee borer in estimating the EILs. These EILs were determined for conventional and organic coffee under high and average plant yield. When the quantitative losses caused by H. hampei were considered alone, the EILs ranged from 7.9 to 23.7% of bored berries for high and average-yield conventional crops, respectively. For high and average-yield organic coffee the ELs varied from 24.4 to 47.6% of bored berries, respectively. When qualitative and quantitative losses caused by the pest were considered together, the EIL was 4.3% of bored berries for both conventional and organic coffee. The EILs for H. hampei associated to the coffee plants in the flowering, pinhead fruit, and ripening fruit stages were 426, 85, and 28 adults per attractive trap, respectively.

Magnetization curves as probes of Monte Carlo simulation of nonequilibrium states.

The influence of parameter choice in the Monte Carlo simulation of zero-field-cooled-field-cooled magnetization curves of granular systems is analyzed. The main simulation techniques are summarized and compared, in terms of the determination of macroscopic quantities usually associated with nanoscopic details of the sample.

Photosynthetic responses of soybean to soybean aphid (Homoptera: Aphididae) injury.

The soybean aphid, Aphis glycines Matsumara, was discovered in the United States in the summer of 2000. Since that initial discovery, the aphid has spread across northern soybean production regions. In 2001, we examined the physiological responses of soybeans to low aphids densities (fewer than 50 aphids/leaf). In this study, we determined photosynthetic rates, leaf fluorescence responses, and photosynthetic responses to variable carbon dioxide and light levels. In addition, analyses for chlorophyll content and stable carbon isotope ratios were used to differentiate potential differences in stomatal versus mesophyll limitations to photosynthesis. We observed rate reductions of up to 50% on infested leaflets, including lealets with no apparent symptoms of aphid injury (such as chlorosis). Differences in fluorescence data indicated that photoelectron transport was not impaired. These results indicate that substantial physiological impact on soybean is possible even at low aphid densities. Also, the conventional view of aphid injury acting through reductions in chlorophyll content and light-harvesting reactions of photosynthesis is not supported by our findings in this system.