How to handle bait-averse cockroach populations

• Effective baiting should show results within a day or two.

• Be ready to switch baits if “the good stuff” is taking too long.

The German cockroach (Blattella germanica) is mounting a comeback. It is becoming increasingly common to find established infestations at accounts. Bait aversion is not resistance as we know it, but it develops for the same reasons and requires similar adjustments from the pest management professional (PMP).

The active ingredients in most baits cause cockroaches to die face down, not on their backs.
Photo: Mark Sheperdigian, BCE

Like resistance, bait aversion develops within a single population and starts slowly — but grows more prominent as long as the same bait is being applied. In the field, we simply notice that there are still many live cockroaches during the follow-up service. This also can be caused by poor application techniques or insufficient amounts.

It can be difficult to tell the difference between sloppy application techniques and bait-averse cockroaches. For those of us who remember resistance issues, though, this will seem familiar.
 

Is the bait working?

On your first return visit, you should be able to see that bait has been consumed. This will be especially evident where the cockroach activity is the heaviest. German cockroaches come out to feed every night. When a lethal dose is consumed, most baits will produce dead and dying roaches within a day. Conscientious clients will have swept them up, but a savvy PMP usually can find casualties in corners and other hard-to-see places.

If all the bait is intact and there is still plenty of activity with no dead or dying roaches, this is a strong indication that they aren’t eating the bait.

Before applying a bait, offer it to the cockroaches right out of the tube if you can find them. They should be willing to walk out of their harborage for a sample of your wares. If they will not come out to eat it, consider changing baits.

This is why it is crucial to have more than one bait available. If you have no bait they deem acceptable, consider stocking some different baits.

Even if you rotate your baits quarterly or on some other schedule, you may encounter bait-averse cockroaches. They may have been freshly imported from another building or facility where the bait aversion has been growing. While there is an ample selection of quality bait products, it is essential that PMPs are also proficient in the use of contact insecticides against cockroaches.
 

Exception to the rule

While most German cockroaches will emerge from their harborage every night to feed, there is one exception: Gravid females (those developing an egg case) will separate themselves from the population and sit quietly without feeding for a week or two. Once the egg case is complete, the females begin searching for food. This results in adult females showing up after much of the population has been eliminated.

Contributor Mark Sheperdigian, BCE, can be reached at shep@rosepest.com.