Answer: It sounds to me as though you've done a fair amount of research into the Walnut Husk Fly. You probably already know that malathion is the chemical recommended by Washington State University for control of the adult flies and that timing is paramount to killing the adults. Malathion is probably not something you'll want to use, given the pets you have. Although the husk flies turn the husks black, the nuts are usually edible, although hard to access through the hardened husks. Aside from chemical sprays, I can only suggest you practice good garden sanitation; raking and disposing of fallen walnuts and leaves at the end of the season. As with all pests, there is a natural predator out there and eventually a balance will be struck. You'll just have to wait until the good insects show up to eliminate the larvae that are causing the damage to your walnuts.
Best wishes with your garden!
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