I have been told that Diatomaceous earth will help with the many slugs that enjoy the buffet that is my garden, since the micro-fossils irritate their slimy bodies. But will it help with other insects and caterpillars, especially gypsy moths? I purchased a bag that says "food grade" but I don't know if it is as effective as non-food grade DE. Any experience in this area would help. This is turning out to be an expensive organic garden this year!
I do not use this in my gardens. I only use it sparingly, in certain areas, for serious infestations.
Slugs love beer. I pour a bit of beer in a shallow bowl, and they crawl in at night and drunkenly drown. (Recycled cat food or tuna tins work well, because you can just throw out the whole ugly mess.) If you don't drink beer, there are slug baits for sale. That being said...
Yes. Food grade Diatomaceous Earth will nonselectively kill all insects and caterpillars (both bad and good). But, it has to be dry in order to work. Even a slight dew will make it ineffective. It does not harm the earthworms under the soil when they eat it.
Do not use the pool grade stuff! It is only meant for use in swimming pool filters, has been linked to health risks and might kill your plants. (In fact, it's recommended that you avoid inhaling even the food grade kind, as it can cause respiratory distress in some people. I just avoid getting it in my eyes.) You are probably (harmlessly) eating some food grade Diatomaceous Earth every day, because grain and vegetables, etc., are stored in it, in the warehouses.
I put a small amount in a "puff" bottle so I can apply it very selectively, and keep the bag sealed against moisture. I bought a plastic bottle for $1 (the type use for ketchup or salad dressing) and that works really well. Some people use a shaker bottle for large areas.
While it supposedly is effective on gypsy moth caterpillars, unfortunately I have been unable to find any sites dealing directly with that ugly problem for advice.
This site is very informative about food grade Diatomaceous Earth. http://www.richsoil.com/diatomaceous-earth.jsp
This one discusses the pros and cons (like concerns about bees), and has suggestions on how to apply it to a garden. http://www.theprairiehomestead.com/2015/07/diatomaceous-earth-garden.html
This site discusses avoiding putting it on the flowers to try and protect the pollinators. http://homeguides.sfgate.com/diatomaceous-earth-garden-pests-84812.html
Used to control slugs https://www.diatomaceousearth.com/natural-slug-control/