Are farm crops getting more resistant to insects disease and other pests?

Yes and no. More resistance is being both bred and engineered into crops all the time. However, the germplasm pool for the major crop classes such as corn, soybeans and wheat is shrinking all the time which leaves the worldwide supplies at more risk should a disease or insect adapt to existing varieties. This is why plant breeders are frequently trying to find new "landraces" (old original plant forms) of crops to breed into existing germplasm to create more varied resistance.