It's been about 18 months since I had any discussion on flea control, in large part because I had done so many exhaustive posts on the topic. Then I received an email from Jon, and felt it was worthwhile briefly revisiting the issue.
For anyone reading this I STRONGLY recommend looking at the post Jon read since it lists all of my previous blog entries on flea issues and will take care of most of the questions people will have. In fact, I won't answer questions that could be covered by reading these posts.
First, let me say that I don't work for Bayer, get paid by them, or own any stake in the company. Heck, I don't even carry their flea products in my clinic! But I have a lot of respect for them as a company and like their flea products. Bayer checks for resistance every year by collecting flea populations from around the world and testing their products against these fleas. So far no resistance has been documented.
Yes, fleas will die when in contact with Advantage. However, it will take hours for this to happen. If you have fleas in the environment then you are continually having new fleas jumping on the cats. So let's say that you are having 5 fleas per hour land on the cat, and it will take 2 hours for those fleas to die. Then do the math. At hour 0 you have five fleas. At hour 1 you have 10 fleas. At hour 2 you see the first 5 fleas die, but you have 5 new fleas as well as the fleas alive from hour 1, leaving 10 alive fleas on the pet. At hour 3 you see this pattern continue. So as long as you have new fleas in the environment you will continue to see fleas jumping on the pets even though the product is killing them. And if you go by the above example, you will always average 10 fleas on the pet until there are no more in then environment. Why five per hour? Simply easy math and it may not be that many (or may be more, depending on the environmental infestation). But I think you get the point on how a flea product can work even though you are seeing new, "healthy" fleas.
A couple of rules of thumb....adult fleas are only 5% of your total flea population, the rest being other life stages. And for ever flea you see there are about 100 that you don't see. By the time you see adult fleas in these numbers on the pets you have a significant problem in the house and yard. If you're not using products designed to treat the environment you will find it much harder to get it under control.
So how long does it take to get an existing flea population under control? A minimum of 2-3 months! And that's assuming proper, ongoing treatment of the pets and the environment. All of that has to do with the flea life cycle: eggs can become adults in as quickly as three weeks, or can take as long as 6 months, so during that time period you have the risk of new fleas hatching out daily for many months.
Jon, I hope you can now understand why the Advantage II isn't giving you immediate relief. Make sure to continue to use it every month on all of your pets, treat your house every 3-4 weeks, and have patience that you probably won't see significant results until closer to Thanksgiving. And make sure to treat throughout the winter, since fleas can live inside year-round!