I know you said you've been using DE already.I really trust this ALL-NATURAL magic powder that works physically and not chemically.Works like a champ for me! I would suggest you give DE another chance.If you can expose the bugs by lifting the nest-box,try direct application right on those pesky critters! They WILL die! Also,be sure the DE you are using is as PURE as possible.PURE DE is a little harder to find,but worth the trouble.I've found that some DE products are greatly diluted - some by over 90%!!! ( the "DE" sold at my local TSC is only 8% DE - 92%=OTHER ) Read those labels carefully.Good,pure DE should also be "Food-Grade" and display OMRI Seal.Remember-DE is a SAFE chemical-free option for us all! GOOD LUCK my friend!