Many insects are not actually the cause of tree mortality but simply “opportunists” and infest decaying wood. Spraying the remaining trees depends on the insects and their propensity for infesting live trees.
Cut wood, especially if infested, should never be moved out of the county to minimize the spread of harmful pests. See more at www.dontmovefirewood.org.
Certified Arborist (International Society of Arboriculture)
Purdue Pest and Plant Diagnostic Center - Walnut tree beetle, http://www.ppdl.purdue.edu/PPDL/current_interest.html#WTCD
Indiana Walnut Council