Some info I found - 

For a start, don't worry about the grasshoppers, they don't need pesticides because by the time you see them, till the time they go is about the same time that it takes for pesticides to work, so using pesticides is a waste of money; use that money to improve the soil around the tree or, give it more water if it is in well drained natural soil.

The tiny black and white catapillar's are a citrus butterfly, they won't do much harm; probably eat a few leaves but that's all so perhaps let them be.

The ants are probably feeding of black sooty mould on the leaves or aphids; to stop them, water the tree!

Don't worry about the white grubs, they eat the wood chips and are a sign of a healthy environment.

Basically, you have a young tree with lots of fresh mulch that is rotting down. To ensure good growth and fruit, keep the tree well watered, well fed with a citrus fertilizer and don't spray because you will not only kill bad bugs but also good bugs.

If the tree, is in deep sandy, fertile soil, in full sun and you water it regularly and also give it feeds of fertilizer, then you will have lots of nice fruit, don't worry about ants and other critters they will disperse over time.

To add, lemon trees need N P K and 14 trace elements. Citrus fertilisers are good.