There are organic pesticides that contain pepper as an active component. It you use this source as a pesticide be sure to allow time for the pepper to dissipate somewhat, or flush the lettuce with water before handling with your hands (pepper can burn your skin), and do not get it in your eyes.
Also, I concur with IsadoraPandora, in the use of neem. Neem is a wonderful oil that does not need t be used full strength for this purpose. Ask Isadora to share with you, her method for mixing up the Neem oil and water spray. She is an excellent teacher from what I notice from reading her hubs.
Good luck growing your lettuce.