Those insects do little more than prune some of the smaller branches from the trees after laying eggs in the part that will fall from the tree. While a major infestation can set a young tree back a bit in almost all cases spraying is not necessary as the tree easily regrows and the insect numbers are not often as bad in future years. Also, spraying is often not effective since you would need to spray before you see the branches falling, prior to the female twig girdlers actually starting to lay eggs and chewing around the branches. One more reason not to spray is that lindane is very harmful if it gets in your eyes and in trying to spray large trees some is often likely to drift down and contact your eyes. Picking up the fallen branches (which contain the eggs) promptly will reduce the number of these insects in future seasons.
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