I got a garden/animal insect dust at the feed store. Is there any withdrawal time, or can you eat the eggs? The feed store didn't know, the can doesn't mention it and I've never heard anyone mention it before... Also, do you have to keep repeating the applications - when, and for how long? I dusted them maybe 2 months ago, and it didn't seem to help a bit. 2 hens have bare, red rumps and the other 3 hens look ok. Thanks.