Say I have a square box with the top open, I want to stop walking/crawling insects to get to the inside of the box from the top edges. I know insects are so good at walking against gravity vertically. What materials can I use to stop them? I guess there are some coatings/surface that are too slippery for them to walk? Or are there some mild non-toxic repellents that can ward them off? Thank you very much.
Fluon works on on smooth surfaces, like metal and glass, and is used by insect keepers for their tanks.
I once successfully used wide double-sided tape with the backing not removed against ants.
If the insects don't swim, you can also put a pan of water under the box with a large enough water gap between the pan and the box.
Use a physical barrier to prevent insects from entering the container. In other words, cover the container.
Using any other method does not ensure that material, including insects, will not fall into the container from the top edge.
Placing sticky or smooth substances in, on, around, or over the edges, still allows entry of some or all unwanted material.
Another way would be to invert the container if the edges were smooth and regular enough to prevent openings large enough for allowing unwanted entry.
Not sure if this will work for what you are trying to do but there is a substance called Diatomaceous earth. It is used for filtering such as in pools and stuff like that.
Most people don't connect that it acts as a mechanical pesticide as well. My uncle owns a goat farm and he says all he has to do is give a little bit of Diatomaceous earth to his goats in their food and it kills all parasites and bugs without harming the goats.
It is made of the fossilized remains of algae / phytoplankton and is apparently safe for larger organisms to eat.
Not sure on the exact science of it but apparently the particles are so small that they physically cut up insects bodies but don't harm us or animals. It's just abrasive to us like pumice but to it's an insecticide to most if not all insects.
My uncle said that he also takes Diatomaceous earth and sprinkles it around his house or anything else he doesnt want ants to get to. It acts as a physical barrier that they cannot crawl across.
So if you are trying to prevent insects from getting to the container you could make a line of Diatomaceous earth around the container and any insect that tries to crawl to the container will die. This will not prevent flying insects however.
Hopefully that helps. I think it perfectly answers your question. Non toxic, prevents insects walking or crawling and allows you to create a barrier to prevent insect entry plus no chemicals or other negative effect pesticides