Small white flys--anybody troubled by them?

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I don't know these--they are total strangers to me, and I wish I had never set my eyes on them. They have utterly destroyed my chilli plants. First they settled on the guava tree and the guava tree survived the onslaught. Now they are after my chilli plants. Small white flies! They settle on the underside of the leaves, and the underside of the leaves turn white too, and the topmost tender leaves of the plant curls up. I tried DDT and they just fluttered about. I don't know what to do with them. Anybody knows what these are? And how I can get rid of them? Cheers and happy mylotting