Food grade diatomaceous earth may help. Here’s some links to give you more info.
http://www.internet-grocer.net/diatome.htm
http://www.ozarkcoop2.com/cgi-bin/catalog.cgi?Inv=4&Category=Non-Food&Comm_Code_Description=Gardening%20Supplies&CatSubHead=Nitron%20Industries&CatProductNumber=52704
http://ighawaii.com/naturally/naturalanimal/de.html