Written by: Stuart Steele
Your insecticide application failed to control the pest- wrong product, poor application, or insecticide resistance?
Rarely does any insecticide application kill all of the target pests. Some will survive either because the application didn’t reach them, they avoided it, or they were exposed but managed to overcome the effects. Pests that are not killed may pass along to their offspring the trait that allowed them to survive.
This genetic insecticide resistance develops when the same insecticide is used repeatedly in the same place, against the same pest. The speed with which inherited resistance develops in a population of insects depends on how quickly each generation is produced, the number of offspring, and how often the insects are exposed to the insecticide. If the same insecticide is applied continually, a higher and higher percentage of the population will become resistant to the insecticide as most of the susceptible insects are killed and only the resistant ones are left to breed. It also means that more insecticide is required to achieve kill of the now largely resistant population.This doesn’t explain why bed bugs were already resistant to our pyrethroid insecticides when they reappeared in this country about 15 years ago. Resistance may have developed first in other countries either from their use of
This doesn’t explain why bed bugs were already resistant to our pyrethroid insecticides when they reappeared in this country about 15 years ago. Resistance may have developed first in other countries either from their use of pyrethroids or as a result of insecticide cross-resistance from exposure to DDT, which has the same mode of action.
The main way to prevent resistance is to rotate the insecticides used in an account. This doesn’t just mean switching to a similar product because you may then have to deal with cross-resistance. It means switching to an entirely different class of insecticides, ideally with a different mode of action. You can also prevent or reduce the effects of resistance by decreasing your reliance on insecticides overall. Practice IPM, using more non-chemical controls such as trapping, vacuuming, and heat treatment.
Insecticide resistance is not the same as avoidance or bait aversion
If you’re old enough to recall when cockroach baits first came out, they worked beautifully for a good long time, even against resistant roaches. Then, some PMPs noticed that the baits weren’t working quite so well and feared that insecticide resistance was rearing its ugly head again. Instead, the problem turned out to be bait aversion, the roaches had developed a distaste for the glucose sugars in the bait. This avoidance or behavioural resistance was passed on to their offspring. Change in the bait formulas to something more palatable to these cockroaches largely solved that problem… for now.