Jumping in the middle here. My understanding (from the literature) is that the Doxy kills Wolbachia bacteria that live symbiotically within nematodes and are essential for worm embryo development. It takes at least 3 wks of Doxy to eliminate the Wolbachia. The worm parasites are not affected by Doxy but they can then be attacked by the IVM (or Moxidectin) and Fenbendazole while they cannot reproduce. Over time their numbers can be reduced overall.