The chemicals you need are:
Clorifos 48, you add 2cc to 1 litre of wáter
Confidor 20, you add 1cc to 1 litre of wáter

You need to treat the trees every 30 - 45 days, alternating the two chemicals.
I treat mine by mixing up 8L of wáter with the relevant chemical and emptying the watering can into as close to the middle of the tree that I can get (it is a bit tricky with all the spines!). Two or 3 watering cans per tree usually does the job.