True. Cockroaches (but also mice and scorpions) resist massive doses of radiation, much higher than those lethal to humans. The same is true for several very harmful chemicals. Of course there are compounds, used in disinfestations, that are able to kill these very resistant insects: synthetic pyrethroids and phosphorganic compounds.

More news for "strong " stomachs
The sweet? How disgusting! So the cockroaches avoid the traps
Lustrous antennas for better smells: word of cockroach
Why do cockroaches die on their stomachs?
Cockroaches: humiliated and eaten