Q.new leaves on young eucalyptus shrivel and die
Our flowering gum is about 5 years old. Every year the new leaves wither and die. In fact, the ends of the thin branches seem to be burnt because they break off and are dead. We have never had flowers. Now a neighboring young red box gum has the same problem. I have searched for insects but have found none, although I have found some spiders’ webs. Can you advise me please?

Certified GKH Gardening Expert
Sounds like you may have thrips. They are very small and hard to spot, but they generally attack the new growth (the tips) or flowers of a plant. You can treat the tree with a pesticide. I personally like neem oil for thrip control on trees. It is systemic and will protect the whole even if you can reach the whole tree with it.
This article will provide more information about thrips:
https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm