It turns out that the amount of insecticide and herbicide that is used with the new GM crops is not a cut-and-dried topic. In some cases, more chemicals are being used, while in others, less. The answer to that question is long and involved (see link below to the study results), but here is the short version (for 2 specific crops: soybeans and maize):
The role of GE crops in shaping the patterns of pesticide use remains a controversial topic. Over the period 1998–2011, our results show that GE variety adoption reduced both herbicide and insecticide use in maize, while increasing herbicide use in soybeans. However, weighting pesticides by the EIQ lowers the difference in herbicide use by GT soybean adopters (such that the estimated average impact over the study period is statistically indistinguishable from zero). Adoption of Bt maize, on the other hand, is associated with a clearer decline in insecticide use.