Final answer:
Spraying insecticides on grazing lands raises concerns about ecological damage, development of resistant 'superweeds', and potential health risks to humans and wildlife.
Step-by-step explanation:
The major concern of spraying insecticides on grazing lands is the potential ecological damage they cause. These chemicals can kill non-target species including natural predators and parasites of pests, which are essential for maintaining a balanced ecosystem. Further, there are human health risks for consumers and agricultural workers exposed to these chemicals. Insecticides may also lead to the development of resistant 'superweeds' and affect other forms of wildlife, potentially disrupting food chains and biodiversity. Moreover, they may interfere with disease transmission patterns by affecting vector populations like mosquitoes and aphids, which could exacerbate the spreading of diseases among plants and possibly humans and livestock.