We learned long ago that insecticide use represents a selection factor in a flea population. The resistant individuals survive and pass their genes on to offspring.  Eventually a resistant population is produced.  We would like to avoid creating a population of fleas who laugh at our best insecticides and there are two ways of doing this:

The first way to avoid resistance:  Change products periodically.

This seems simple and even obvious. If you want to make a resistant population then keep exposing the population to the same insecticide and after enough generations your population will be resistant.  If you switch to another insecticide, the group will be totally sensitive to the new insecticide.  After a few more generations, change again.

Working against this method is the fact that advertisers encourage people to continue to use a product they like and this is, in fact, what people tend to do.  The power of marketing is strong though, technically, it is better in the long run if a household alternates between two flea products each year.

The second way to avoid resistance:  Use a flea sterilizer.

A group of fleas that survives exposure to Frontline^® or Advantage^® cannot pass on their resistance genes if they have been sterilized by a second product.  Program^® interferes with the production of chitin (the hard material making up the insect exoskeleton).  The adult flea has already made its chitin but its off-spring need to develop a chitin egg-tooth to escape their eggs after development into larvae.  A larva whose mother has had a big drink of lufenuron-laden blood will not be able to hatch.

Another such sterilizer is Methoprene (the “plus” in FrontlinePlus^®). Methoprene was developed as an additive to flea sprays and foggers.  It is totally non-toxic (it does not even kill fleas) and represents a group of insect control agents called “insect growth regulators” or “juvenoids.” Methoprene mimics a youth hormone of the flea so that larvae who consume it in flea dirt cannot mature and eggs laid by female fleas who have been topically treated with it cannot develop. Twenty years ago, this compound was a miracle in flea control. It enabled the life cycle to be broken in two places for the first time. Now methoprene is rather “old hat” but it has been included in Frontline to prevent Frontline resistance.

Resistance is an important phenomenon and it should not be ignored. Our clients may inadvertantly be promoting resistance without realizing it.

Listen for this clue:

• At first the product worked really well but now I have to apply it again after 2-3 weeks. It doesn’t last the whole month anymore.
  
  When someone starts to use the product more frequently in this way, they are increasing the selection pressure and creating resistance more rapidly. What they should do in this situation instead, is add a sterilizer or change to another product.

In conclusion, fleas are here to stay one way or the other.  Know as much about this pest as you do about the dogs and cats that it feeds upon.  You cannot know too much when it comes to flea control.

Last updated: August 31, 2002