Tomato plants contain a natural alkaloid [glycoalkaloid] called tomatine sometimes referred to as lycopersicin which possesses antimicrobial, fungicidal, and insecticidal properties. Other Solanaceae Alkaloids found in the tomato plant also have similar properties. Insects particularly herbivorous insects that chew leaves or suck sap can be combated with this alkaloid and it is something you can easily make yourself.
How to Make Tomato Leaf Spray
Mash up several cups of tomato leaves and soak them in luke warm water overnight. The following day strain it with a fine strainer, cheesecloth or even a coffee filter, be sure to squeeze the leaves just as if you were making a cup of tea and squeezing out every last drop of essence. There should not be an over abundance of visible residue floating in the solution when you shake it. If there is you may want to strain it again. It's a good idea to add another cup of water to the solution before putting it in a spray bottle, but it is not absolutely necessary.
Apply your Tomato Leaf Spray as a mist on the stems and leaves of infested plants, be sure to spray the undersides of the leaves where many tiny critters such as aphids congregate.
Tomato leaf spray will not be as effective on tomato plants as it is on other plants. The reason being that insects that tend to prey on tomato plants have developed somewhat of a natural resistance to it over eons of evolution. It is helpful on tomatoes but more effective on other plants in your garden.
In addition to being useful as a pesticide tomatine will inhibit the growth of various fungi and bacteria [Open Chemistry Data Base - Tomatine]. - It is even synthesized and marketed commercially.