I don't see insects but you can bring a sample of your Japanese Maple into the Denver Extension office at 888 E. Iliff so we can do a closer examination.
I suspect that this is sun/heat damage. Japanese Maples like morning sun but need protection from intense afternoon sun. They prefer more humid conditions than we have on the High Plains. Make sure you give your tree enough water to compensate for the water it loses through transpiration and make applications of water frequently enough so the roots are consistently moist - not fluctuating from wet to dry and back to wet again.