A third consecutive overall index drop in a monthly rural bankers survey suggests an economic slowdown is ahead for rural parts of 10 Western and Plains states. The Rural Mainstreet Index sank to 44.4 this month from 49.0 in September and 50.0 in August. The overall index is computed from various economic category scores, and survey organizers say any score below 50 suggests that factor will decline. Creighton University economist Ernie Goss oversees the survey, and he says the overall index reflects ``weakness stemming from lower agriculture and energy commodity prices and from downturns in manufacturing exports.'' Bankers from 10 states, including Illinois, were surveyed.