South Dakota has been a leading adopter of genetically modified organism (GM) crops since their introduction in 1996. In 2009, South Dakota shared the top adoption rate with Iowa for the percentage of acres planted with Bt corn. However; South Dakota has also recently experienced a significant increase in the proportion of acres treated with insecticide. The empirical evidence presented suggests that corn, hay and sunflower production in South Dakota have experienced an intensification of insecticide use in 2007 relative to past US Census of Agriculture reporting years. This study links the proportion of acres planted for a specific crop to the proportion of total acres treated with insecticide at the county level. This approach provides insight on how changing cropping patterns in South Dakota have influenced insecticide use. Empirical results indicate that the upper-bound estimate for insecticide usage on non-Bt corn acreage increased from 38% in 2002 to all non-Bt corn acres planted in 2007. The implication of this result is that in 2007 South Dakota producers were likely treating a percentage of their Bt corn acres with insecticide. Changing cropping patterns in South Dakota are also compared to that in other states in the US Corn Belt region. It appears that the South Dakota experience is not unique and is part of a broader trend.