Temporal Changes in Cereal Aphids (Hemiptera: Aphididae) Populations in Northern Rio Grande do Sul, Brazil

Cereal aphids (Hemiptera- Aphididae) are economically important pests in all wheat-producing regions of Brazil and about eight species can be found in wheat crops. Aphids acquired the condition of severe pest in wheat in the 1970s, due to the emergence of Metopolophium dirhodum and Sitobion avenae. A successful biological control program of wheat aphids was introduced in southern Brazil in 1978. This study describes temporal changes in aphid populations in a wheat producing area in the northern region of Rio Grande do Sul (RS) state, Brazil. Data from weekly samples (water traps of Moericke type) for the current (May to November 2008, 2009 and 2010) population frequency of each species was compared with 1970s populations. In addition, their seasonal fluctuations and the influence of rainfall and temperature on their populations were estimated. The species collected, and their frequencies, were as follows- Rhopalosiphum padi (57.6%), Sitobion avenae (31.0 %), Schizaphis graminum (7.7%), Metopolophium dirhodum (1.4%), Rhopalosiphum rufiabdominalis (0.9%), Rhopalosiphum maidis (0.6%), Sipha maydis (0.4%) and Sipha flava (0.4%). Aphids populations in winter cereals in northern RS have changed radically. The high populations of M. dirhodum in wheat in 1970s have been reduced to such levels that rarely have been found. Nowadays, R. padi was the predominant species. When the rainfall remained between 0-20 mm and temperatures between 15-20 ºC, aphid populations were more numerous than the average for the sampling period.