Feb 22, 2012 – Is Resistance Forever?
QUESTION:
My question is concerning pesticide resistance and cockroaches. I realize that rotating the pesticides and type of pesticides is a good method for avoiding pesticide resistance, but if you do have pesticide in your inventory that roaches have developed resistance to would it be possible to bring that pesticide back into rotation 9 to 18 months later? My thinking is that the product should be out of rotation long enough and the resistance developed could possibly be defeated because they have not been exposed to that particular material in a while.
ANSWER:
I would say that bringing back a product within just a year, when you believe that resistance to it is being shown, would be far too early. And, as we have seen with the Common Bed Bug and its resistance to pyrethroids, the development of resistance is an evolutionary phenomenon that could linger in the genetic makeup of an organism for a very long time. Because of the constant exposure to DDT when it was first introduced for bed bug control these bugs quickly built up resistance to the molecule, and this resistance was an ability to block the effect - the mode of action - of that molecule on the nervous system of the bed bug. Synthetic pyrethroids were introduced 3 decades later and really not even used heavily on bed bugs for another 20 years, but because the Mode of Action of pyrethroids is exactly the same as the Mode of Action of DDT the resistance popped up rapidly. Clearly the offspring of those bed bugs back in the 1950's still had the mechanism for resistance built into their genes.
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My question is concerning pesticide resistance and cockroaches. I realize that rotating the pesticides and type of pesticides is a good method for avoiding pesticide resistance, but if you do have pesticide in your inventory that roaches have developed resistance to would it be possible to bring that pesticide back into rotation 9 to 18 months later? My thinking is that the product should be out of rotation long enough and the resistance developed could possibly be defeated because they have not been exposed to that particular material in a while.
ANSWER:
I would say that bringing back a product within just a year, when you believe that resistance to it is being shown, would be far too early. And, as we have seen with the Common Bed Bug and its resistance to pyrethroids, the development of resistance is an evolutionary phenomenon that could linger in the genetic makeup of an organism for a very long time. Because of the constant exposure to DDT when it was first introduced for bed bug control these bugs quickly built up resistance to the molecule, and this resistance was an ability to block the effect - the mode of action - of that molecule on the nervous system of the bed bug. Synthetic pyrethroids were introduced 3 decades later and really not even used heavily on bed bugs for another 20 years, but because the Mode of Action of pyrethroids is exactly the same as the Mode of Action of DDT the resistance popped up rapidly. Clearly the offspring of those bed bugs back in the 1950's still had the mechanism for resistance built into their genes.
However, according to some of our industry experts, The Common Bed Bug is a remarkable creature with an amazing propensity for developing resistance to MANY kinds of chemicals, whereas German roaches do not have quite the same ability. There definitely have been pockets of German roaches around the country where resistance has been demonstrated, but it takes a lot longer and is not nearly as widespread as with bed bugs. If we assume that the development of resistance is simply evolution in action - the survival of those individuals most suited to their environment - then when we constantly use a particular toxin we could continue to select for the survival of the resistant individuals and their subsequent generations. They became resistant simply due to a new hazard in their environment, and it's possible that if that hazard is removed the species could "evolve" back to what was working previously, eliminating the genetic resistance and making them susceptible once again.
But, this is just my speculation, and the better path to take would be to avoid developing that resistance in the first place by rotating your product usage on a regular basis. You would need to rotate to some other chemical family that has a different mode of action, and our new course in Master Technician - number 209 Insecticides Modes of Action - may be helpful in understanding this. Since all pyrethroids affect the roach in the same manner the resistance to one active ingredient should also show resistance to all other pyrethroids, as well possibly as to other chemical families with the same MOA.
German roaches breed pretty quickly, with 4 generations each year possible, so they would be more likely to revert to "normal" than perhaps other species that take up to a year to mature and produce offspring. Of course, this short life cycle from egg to adult is also a reason why resistance can develop more quickly in the German Roach, as you more quickly get a group of offspring in which there may be a few resistant individuals. Because of the relative rarity of resistance by roaches it is far more likely that failures in eliminating these roaches from an account will be due to something other than resistance, such as missing pockets of the roaches in a treatment program or having more roaches enter the account.
I like a comment made by Dr. Dreydon during a seminar on fleas years ago. He briefly commented on fleas and resistance to insecticides, which is often touted as the reason technicians are unable to eliminate a flea problem. He said, with respect to resistance, "it's a crutch".
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