Populations of voluble bean aphids in monoculture and in association with maize

Abstract

The populations of aphids vectors of the bean common mosaic virus (BCMV) are favored during dry seasons with the consequent in­crement of the disease incidence in the crop. With the purpose of obtaining genetic or cul­tural alternatives to this problem, a study was focused to quantify the virus incidence and the aphid populations in seven bean genotypes planted in monoculture and associated with maize, during the first semester of 1992. A randomized complete block design with three replications was used. Virus incidence, aphid species, number, and size of the colonies present in three strata of the bean plants were evaluated during the pod formation stage (R 7). The incidence of BCMV in all bean genotypes planted in association with maize was lower (12,4%) than the registered in the monoculture system (25,7%). The most abundant aphid species found in both Culture systems were Aphis gossypii Glover, Picturaphis brasiliensis (Moreira), and Myzus persicae (Sulzer), predominating the colonies with 1-10 individuals. In monoculture, the bean geno­types with greater aphid populations were Frijolica L.S. 3.3, Radical, and LAS 300. Ne­vertheless, in all bean genotypes the aphid populations were lower when associated with maize than in the monoculture system. Ge­notypes ICA Viboral, Radical, LAS 300, and LAS 315 were outstanding because they showed reductions up 50% in the population colonies of A. gossypii and M. persicae, important vectors of the BCMV. In the bean monoculture system, A. gossypii developed colonies of all sizes (1-10, 11-50, >50 individuals) with the same proportion on the three plant strata; but when beans were planted associated with maize, the aphid colonies located preferentially on the lowest stratum.