No abstract

Among the aphids associated with wheat and other winter cereals, Rhopalosiphum padi (L.) is currently the predominant species in the wheat growing region of southern Brazil. The damage caused by this aphid occurs by direct feeding and/or by the transmission of pathogenic viruses, such as the Barley/Cereal yellow dwarf virus. In order to estimate the direct damage caused by R. padi on wheat, we evaluated the population growth of this aphid during the tillering and elongation stages and its effects on grain yield components. The experiment was conducted in a screenhouse with three wheat cultivars (BRS Guabiju, BRS Timbaúva, and Embrapa 16). The effect of a period of 16 days, starting from an infestation of 40 aviruliferous aphids/plant, was evaluated and compared to non-infested plants. In both stages, the population growth of R. padi was lower on the BRS Timbaúva. Although infestation caused a reduction in the grain yield of the three cultivars, this effect was lower for BRS Timbaúva. The cultivar Embrapa 16 supported higher infestations and was more tolerant to damage than the BRS Guabiju.

Determinou-se em laboratório a eficiência de inseticidas contra Sitophilus oryzae (L.) (Coleoptera: Curculionidae) e Rhyzopertha dominica (Fab.) (Coleoptera: Bostrichidae) em milho (Zea mays) a granel tratado. Cada tratamento, constituído por 1,2 kg de milho, foi tratado por meio de um pulverizador equipado com bico pneumático usando-se 5 ml de calda/kg de milho. Quinze dias após os tratamentos 200 g de milho, de cada tratamento, foram infestadas com 40 insetos adultos de cada espécie, sendo este procedimento repetido a cada trinta dias até completar 180 dias. A contagem do número de insetos mortos foi realizada 15 dias após cada uma das infestações, desta forma foram feitas avaliações aos 30, 60, 90, 120, 150 e 180 dias após a aplicação dos inseticidas. Após 180 dias esfenvalerate + fenitrothion + butóxido de piperonila, esfenvalerate + fenitrothion e fenitrothion + deltametrina + butóxido de piperonila foram eficientes contra S. oryzae e R. dominica. Fenitrothion foi eficiente contra S. oryzae e deltametrina + butóxido de piperonila contra R. dominica. Esfenvalerate + butóxido de piperonila e esfenvalerate mostraram-se ineficientes contra S. oryzae, o mesmo sendo observado para fenitrothion contra R. dominica. O uso de misturas de organofosforados e piretróides foi mais eficiente contra S. oryzae e R. dominica quando comparado com o uso isolado destes inseticidas.

UK variety used as reference. Bioassays were conducted to evaluate the development and fecundity of both aphids when grown on the wheat genotypes. Although BRS Guabiju and BRS Timbau´va were among the genotypes showing the highest susceptibility and resistance, respectively, against both aphid species, no correlation could be found between DIMBOA levels and antibiosis effects. The cultivar BRS 327 was among the genotypes showing lower intrinsic rate of population increase for the two aphid species. Elucidating the role of secondary metabolites in plant resistance to aphids and the characterization of the genotypes that allowed reduced development of R. padi and S. avenae are important steps to achieve a better natural resistance in hexaploid Brazilian wheat.