First of all the ants are not a pest in the garden. The actual culprits could be several things and until you get an identification on the pest(s) it is difficult to specify the best and safest control.
Many pests can be nocturnal feeders, so you seldom see them feeding during the day. Do some Sherlock Holmes investigative work. Go out at night with a flashlight and inspect the plants, making sure to turn over some leaves.
The remedy will vary depending on what you find. B.t. is an effective control for caterpillars and is sold in many garden centers under a variety of brand names. Pyrethrin/rotenone sprays are effective against beetles, caterpillars and several other pests. While organic, they are more toxic than B.t. Grasshoppers are generally too migratory to effectively control with sprays. Rowcover fabrics can help deter them from eating your plants but may not be a practical option due to their appearance and the size of the plants to be protected. Slugs and snails can be kept at bay by a number of means including iron phosphate bait products should they turn out to be the culprit.
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