Thanks for all the tips guys.
Posting pics of the damaged tweeter and my speaker mounting.
The ants returned at night on Friday but after a second spraying of the surrounding areas, they are gone.
@Suri, I don't have pets right now although I love them dearly, but even then I am averse to chemicals around the house.
@Venkat, I've seen the paste you mentioned - used in the coffee machine @office. The toxic smell frightened the hell out of me then and I stopped using the machine long back when I found out how they were maintaining it.
Putting boric powder today. And yes, I think I will open the speakers and leave them in the hot sun for short while to ensure there are no eggs deposited on the inside. Good idea.
Thanks again for all your suggestions. Meeting SoundsGreat this afternoon, then will decide what to do.
Bigger pic of tweeter here:
http://img10.imageshack.us/img10/4092/speakers0.png This one is a good close-up of the damage.
Regards