Answer: Let's see if we can clarify things. It sounds as though you are storing bark chips for use as a potting medium for orchids. If this is true, and if you're finding insects, you can banish them by simply spreading the bark chips out on newspapers and exposing them to the fresh air and sunshine. After leaving them outdoors for a day or two, scoop the bark chips up and store them in a clean container. Exposure to the hot sunshine should drive away the flying insects and literally cook any crawling insects.
If you're not storing chips but rather are having problems with insect pests in your potted orchids, the best way to rid your plants of fungus gnats and their larvae is to repot in fresh potting medium. Brush off as much of the old potting media as possible, wash out the pots with hot soapy water, then repot your orchids using fresh potting mix.
Best wishes with your orchids!
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