A bug duster is just a mechanical way of taking dust of any kind and dispersing it in the air. You blow the dust at the underside of the plants, but it ends up allover everything in the end. The stuff doesn't hurt worms or fish. You should wear a dust mask though. DE is not poison. It is a silica dust. It is only effective on soft bodied insects.

Here is a product for this I bought years ago and love it:
http://www.earthworkshealth.com/detail. ... 5Qod-lEMjQ