Anything with petroleum distillates is deadly poisonous to chickens. It's the active ingredient in all wasp killers and most insecticides.
If it works by enzymatic action, it's safe. This would be an organic pesticide which is biological not petroleum based.
You need to get your brother to insist the exterminator reveal the active "natural" ingredient in the pesticide. I've had someone share with me on two different occasions a natural, sure-fire wasp killer, and each time I ended up with a dead hen.
If the exterminator refuses to reveal the...