Pesticides destroy, repel or mitigate pests (an organism that attacks or competes with a crop). A 2014 meta-analysis covering 147 original studies of farm surveys and field trials, and 15 studies from the researchers conducting the study, concluded that adoption of GM technology had reduced chemical pesticide use by 37%, with the effect larger for insect-tolerant crops than herbicide-tolerant crops. Some doubt still remains on whether the reduced amounts of pesticides used actually invoke a lower negative environmental effect, since there is also a shift in the types of pesticides used, and different pesticides have different environmental effects. In August 2015, protests occurred in Hawaii over the possibility that birth defects were being caused by the heavy use of pesticides on new strains of GM crops being developed there. Hawaii uses 17 times the amount of pesticides per acre compared to the rest of the US.