Cockroach killing

my wife is too afraid of cockroaches,one fine day i heard scream of my wife.she saw a cockroach and was screaming. i asked her totake the killing spray and to spray on the cockroach.she took the spray and turned to me and said,"THIS SPRAY IS ONLY TO KILL THE MUSQUITOS," andhow can it works for the cockroach,I said to her. "Don't show the lable to the cockroach"