Answer: Without knowing what kind of tree, it's difficult to identify the pest. They could be beetle grubs (look for boring holes in the branches or trunk), or they could be the larvae of moths or butterflies (look for feeding on the foliage). It's hard to control pests of this sort if the tree is large. If it is small enough for you to reach all the branches and leaves, you can spray Bt to kill off the pests. Otherwise, you may have to just wait for them to mature and leave on their own. There's a nice balance in nature - when the population of pests becomes large, beneficial, predacious insects usually arrive to keep the population under control.
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