Socialist Party presidential challenger Marina Silva has pulled into the lead in the heavily populated states of São Paulo and Rio de Janeiro, according to the latest polls in those regions. Polling from the Ibope opinion research institute showed Ms. Silva with support from 39% of respondents in São Paulo, compared with 23% for incumbent Brazilian President Dilma Rousseff of the Workers’ Party. Social Democrat Party candidate Aécio Neves has support from 17%. In Rio de Janeiro, Ms. Silva leads Ms. Rousseff by a margin of 38% to 32%. Mr. Neves trails in distant third there with support from 11%. Ibope heard a total of 3,400 voters in the regions in two separate polls, each with a margin of error of 2 percentage points. Ms. Silva, a former senator and well-known local environmentalist, has soared into the lead in the last month after substituting former socialist candidate Eduardo Campos, who died in a plane crash Aug. 13. Brazil is scheduled to hold nationwide general elections on Oct. 5.