That unsuredness may be true about the collective data here but we definitely know that one particular species is in precipitous decline - the Monarch butterfly with it's 3400 mile annual journey to go north/south with the seasons. Since they only eat one plant, we could eliminate some causes directly (although they could be secondary causes - like making other plants/insects thrive).

https://www.csmonitor.com/Science/2016/0301/Mexico-s-monarch...