Shieldtox All Insect Killer Citronella is specially formulated with natural citronella oil to effectively kill all insects including flies, mosquitoes and cockroaches. To kill flying insects, close all doors and windows and switch on the lights before spraying. Spray upwards throughout the room for about 4-5 seconds. For instant action, spray directly at insect. To kill crawling insects, spray directly at the insect for 2-4 seconds for instant results.