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Cockroaches are not only a creepy nuisance but they are also a threat to our health. Cockroaches carry bacteria such as salmonella and can trigger asthma in children. If that wasn’t bad enough, thanks to a pesticide-resistant evolution, they might be nearly impossible to kill.

Cockroach pesticide resistance

We’ve all heard cockroaches can survive nuclear disasters but now they’re resistant to modern pesticides. Exterminators have their work cut out for them. A study done by Purdue University showed evidence that German cockroaches known as Blattella germanica L. are becoming hard to eliminate. These cockroaches have developed a resistance to exterminators’ best-known pesticides. The problem in urban areas is becoming particularly bad. It is especially difficult to eliminate these pests in low income and federally subsidized housing. In these communities, resources are low and it’s difficult to effectively fight the insects. According to the study, cockroaches are developing resistance to multiple types of pesticides that have normally been successful in the past. It’s becoming almost impossible to kill these pests using only chemicals.

When it comes to insecticides, not all chemicals are the same. Some insecticides degrade the cockroaches nervous system while others attack the exoskeleton. Chemicals also differ in the amount of time that they need to be left out. Cockroaches and many other insects have developed a resistance to one or more of the most commonly used insecticides. A cockroaches’ lifespan is only around 100 days. That means that the resistance can evolve very quickly. The genes from some of the cockroaches that are resistant are being passed on to the next generation.

The study

Different classes of insecticide work in different ways to kill cockroaches. Typically different mixtures of multiple classes are used and changed from treatment to treatment. This means that if a small number of cockroaches are resistant to one class of insecticide than a different class of insecticide will kill them. The recent study tested these methods in multi-unit buildings in Indiana and Illinois over a six month period.

In one treatment, different classes of three insecticides were rotated each month for three months. This process was then repeated. In the second test, researchers used a combination of two insecticides from different classes for a six month period. In the third test, researchers chose one insecticide and used it the entire time. This insecticide is one where cockroaches had a low-level starting resistance. In each location, cockroaches were also taken out before the study began. These cockroaches were lab tested to determine which were the most effective insecticides for the different treatments. This set the scientists up for the best possible outcome. The roaches were able to be tested first so that you could see which had resistance.

The results and what they mean for the future

Even with rotating the three insecticides, the researchers weren’t able to reduce the cockroach population. The roaches remained flat over the six month test period. The test with the insecticide mixture didn’t work at all and ended up having an increase in the cockroach population. In one of the single insecticide tests, the researchers found that there was little starting resistance. Over the six month test period, the cockroach population was almost all eliminated. With the final test, there was ten percent resistance and the cockroach population grew. The cross-resistance was likely a key factor in the results of these tests. A percentage of the cockroaches tested were resistant to a certain class of pesticide. The cockroaches that live through treatment have offspring that end up being immune to the insecticide from then on. These roaches have also gained resistance even if they haven’t had any previous exposure. The baby cockroaches gained immunity from their mothers.

Female cockroaches can have up to 50 offspring in their three-month reproductive cycle. If a small percentage of the cockroaches that are resistant to an insecticide gain a cross-resistance, you could see a population explosion within a few months. This is where an integrated approach is critical. This form of pest management is crucial to reducing the population. A recommended approach to reducing the cockroach population includes a combination of chemical traps and improved sanitation. This includes vacuums that remove cockroaches. This combination of pest control efforts is more expensive than just using chemicals, however, if the chemicals aren’t working, you’re just throwing away money. This means that the standard approach we previously used to kill cockroaches could potentially be useless. We will need further genetic testing to see how the cockroaches are evolving.

The health problems caused by cockroaches

The German Cockroach only lives in human environments. They are a threat to our health because they produce so many asthma-triggering allergens. They have antibiotic-resistant microbes which continue to contribute to unhealthy indoor areas and homes. Cockroaches carry dozens of different types of bacteria. Some examples of these bacteria are E. Coli and salmonella. These can cause a lot of sicknesses in humans. Cockroaches also leave behind feces and saliva. Between the feces, saliva, and body parts these pests leave behind, there are a lot of allergen and asthma triggers associated with cockroaches. In addition to triggering allergens and asthma, they can also even cause these conditions in children.

Many exterminators are now adopting the integrated pest management approach. Setting traps and cleaning debris off of floors and surfaces is our first line of defense against these creepy home invaders. In addition to cleaning, chemical treatments, and vacuuming, could be our only hope of destroying these household pests.