No amount of pesticides seems to get rid of them. They just keep coming back year after year. Now scientists think they've figured out a way to beat the hardy cockroach birth control.

'Cockroaches - specifically, the brown-banded and the German cockroaches - are the number one urban household pest in terms of frequency'

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Cornell University entomologist Jeffrey Scott says that in order to reduce roach populations without bothering other insects or humans, what's needed is a birth control method that's effective and non-toxic.

Scott and Cornell graduate student Zhimou Wen moved closer to that goal when they cloned five genes from the German cockroach, including one which has a definite but puzzling role in the male roach's reproductive organs.

Scott says they still don't know what hormone the gene is regulating but research points to it as essential for reproduction. "If we can knock out the CYP6L1 protein, we can make the pest struggle to reproduce," Scott says.

After identifying the relevant hormone or other protein produced by the genes responsible for reproduction, Scott says, the next step would be to develop chemical inhibitors of that protein and include those in roach bait.

The result could be a pesticide that attacks only specific pests and not other insects or animals.

But Scott says more research is needed. "Don't expect roach birth control on your store shelves tomorrow."