Their sucking causes distorted foliage and poor growth. They may also spread tobacco mosaic virus, a disease fatal to tomatoes. A strong spray of water will wash them off, but you will have to repeat the treatment often. You also can use a commercially prepared insecticidal soap, available at garden centers, to suffocate them. Or put a couple of tablespoons of hydrogen peroxide in a gallon of water and spray the plant regularly.
Aphids are a favorite food for ladybugs.
An occasional problem on tomatoes and citrus, stinkbug is a shield-shaped bug about a half inch long. It can be green, black or brown and can leave a foul odor on your hands if it is handled. Stinkbug punctures the fruit and sucks out the juices. The best control is to remove weedy areas where they hide close to the tomatoes. If you continue to have problems, dust the fruit with diatomaceous earth or spray with insecticidal soap.