Products are labelled as organic if they are derived from natural materials and not synthesized in a lab. Aside from bacteria or plant extracts that act as poisons, a few organic products can be used as barriers to keep some garden pests at bay. Remember, organic does not mean that a particular product could not harm pollinators, wildlife or humans.
Diatoms (single-celled algae with silica cell walls) that were deposited in large areas and formed into rock are known as diatomaceous earth. It is soft and easily pulverized. Diatomaceous earth comes in food grade, a coarser type for pool filtration systems and a grade for use in the garden.
In gardening, it is used to create an abrasive barrier. The crushed silicon particles create small cuts in the pests that walk over it, causing them to dehydrate. It can be sprinkled on the ground around susceptible plants to keep slugs away or cutworms from attacking tender plant stems. If sprinkled on tomato or eggplant leaves, it will reduce the number of flea beetles and aphids. Do not apply to any fruit or leafy vegetables that you will be consuming. It does not work when wet, such as after a rain or when covered with dew. It will work again when it dries out. However, it needs to be reapplied after a heavy rain. Do not apply to flowers, since it is toxic to bees.
Kaolin clay is named for a clay mineral, Kaolinite. Sold as Surround, it is a fine powder, which must be mixed with water and applied as a spray. It works as a barrier against flea beetles, Japanese beetles, stink bugs and a number of other pests. Applied to leaves, it can reduce foliar damage. I have targeted a portion of the pumpkin stems close to the soil line where the squash vine borer normally lays her eggs. It is also used on apples to repel coddling moth. But note, kaolin clay may be difficult to wash off. It needs to be re-applied after it wears away, after a heavy rain, or when new growth emerges. It will not harm pollinators.
Use dust mask and eye protection when handling the above two products. This precaution will prevent breathing in the dust or having it irritate your eyes.
The use of garlic as an insect repellant has a long history. It can be inter-planted with susceptible crops. But it can also be used to make a spray. Garlic Barrier (a commercial preparation of concentrated garlic) just needs to be mixed with water. Reportedly, it becomes odorless in a few minutes. It is nontoxic to bees, but I would avoid spraying it on flowers. It needs to be reapplied after a rain. It can be an eye irritant, so watch where you aim.
When using any sprays, be mindful of wind direction to avoid drift onto non-target plants. It is best to have these barriers in place before the insect pest arrives on the scene.