Insecticides used were kindly donated by Bayer of Mexico with the following purity: AM: 70%, PM: 62.8%, OM: 70% and MET 48.3%, and CAS numbers 86-5-0, 298-00, 122852-42, and 10265-92-6, respectively. NL20 and HaCaT cell lines were urchased from ATCC; culture medium Ham's F-12,