Answer: Littleleaf linden (Tilia cordata) are hardy trees and can remain pest-free if you maintain their health by protecting from injury, providing adequate water, and spacing them far enough apart to allow them to reach their full mature height and width. There are a number of insect pests that bother lindens, but healthy trees can be less of a target than trees under stress. Control of insect pests is specific to the pest, so unless you there's an insect actually doing damage, there's not much reason to spray.
Keep your trees healthy and happy and they'll be able to deal with an occasional insect attack. If there currently are pests attacking your trees, have them identified and choose a treatment method that is known to control that pest.
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