Summarize the following:
You want to avoid bug bites when camping. Before adding your leaves to the shelter, sift through them to check for bugs. If you have a rake, raking through the leaves first may help remove any bugs. Carry insect repellent that contains DEET when camping. This can help prevent mosquito bites. While leaves can work on a lean-to, it may be safer to pin a tarp up for insulation. You are less likely to be exposed to bugs this way, and the insulation may be greater. Try to remember to bring a trap each time you go camping. Hypothermia is a real concern when camping, especially if you're using a shelter like a lean-to. If you live in a cold area especially, make sure to bring adequate bedding and clothing.  Always bring a plastic ground cloth to lay down under your lean-to. Wear many layers of lightweight clothing.

Summary:
Check your leaves for bugs. Carry a tarp when camping. Make sure you have adequate bedding.