Conservation Midwest bumble bees declined with more farmed land, less diverse crops since 1870 (University of Wisconsin-Madison) As farmers cultivated more land and began to grow fewer types of crops over the last 150 years, most native bumble bee species became rarer in Midwestern states. Recent research reveals that these species declined while the average number of different crops grown in these states was cut in half and as modern agriculture began to focus on intensive production of corn and soybeans.