With freely available satellite imagery you're looking at a 10x10m resolution per pixel.
So basically entire tree stands have to die or crowns have to lose their leafs for it to be detectable form space.
Main insect of concern are bark beetles (ips typographus for spruce, ips sexendtatus for pines) which disrupt the cambium causing a gradual vitality decline until you have dead standing trees. In satellite imagery this is visible as irregular brownish-red patches.
On the other hand there's gypsy moths (also known as spongy moth, Lymantria dispar) which affect the leafs directly, causing large scale temporary defoliation in broadleafed trees usually in the middle of summer.
There's hundreds more insects but few have the capability to cause large scale die-off in trees which are grown in monoculture (pine/spruce/beech).
With freely available satellite imagery you're looking at a 10x10m resolution per pixel.
So basically entire tree stands have to die or crowns have to lose their leafs for it to be detectable form space.
Main insect of concern are bark beetles (ips typographus for spruce, ips sexendtatus for pines) which disrupt the cambium causing a gradual vitality decline until you have dead standing trees. In satellite imagery this is visible as irregular brownish-red patches.
On the other hand there's gypsy moths (also known as spongy moth, Lymantria dispar) which affect the leafs directly, causing large scale temporary defoliation in broadleafed trees usually in the middle of summer.
There's hundreds more insects but few have the capability to cause large scale die-off in trees which are grown in monoculture (pine/spruce/beech).