German cockroaches are one of the top pests PMPs face on a very regular basis. These are known not only for being unwanted house guests, but also for their ability to mechanically vector pathogens and trigger allergies in the people they live with. Control of these unsanitary pests can be accomplished using several products in a PMP’s IPM toolkit.

Buckle up to get excited about insecticide modes of action because I promise this is really cool. Isocycloseram is part of a new insecticide class called isoxazolines which target GABA-gated chloride channels as allosteric modulators. This is a new IRAC group 30 that targets the insect’s nervous system. If you have heard of the human medication gabapentin, you may be familiar with it as a treatment for nerve pain or it calms down overactive nerves. GABA is the thing that calms your nervous system down so think of this insecticide as the opposite of this. It messes with GABA and overexcites the nervous system leading to the eventual death of the insect.

A new IRAC group is a huge deal. Insecticide resistance with urban and structural pests can cause persistent infestations of tough-to-kill pests. German cockroaches have shown resistance to some insecticides in some populations but with this new product, the hope is that nothing will be resistant yet since nothing has seen it. A world of opportunity! Now, this isn’t yet commercially available but with continued research, we get closer every day. German roaches are however known to develop resistance quite quickly even against new chemicals. Keep all that in mind.

Cut to the research scene. In this case, they got the insecticide to use as the active ingredient 1% solution in a gel bait.

The researchers collected a susceptible lab-reared strain and several field-collected populations so the real ones were out on the streets. For these 6 total strains, they ran a series of tests to see which baits were the most effective which meant the highest mortality rate. In the tests, the isocycloseram bait performed comparably meaning it was similarly effective in some tests to the other baits tested which included several commonly used baits on the market. The resistant and susceptible strains reacted similarly to the iso bait which indicates that cross resistance was not found.

 Meaning that resistance to some other baits didn’t carry over and work against this new one. This is a good thing! It is important to note that another common ingredient, fipronil is also related to the GABA channels and the resistance to fipronil did not carry over to any resistance to isocycloseram. They also found that PBO, a synergist, added to the efficacy of the product against the one strain it was less effective against. It is important to note that bait performance is also affected by other ingredients in the bait such as the parts that make it tasty.

Adding another active ingredient and another IRAC group that can be used against these pests will help reduce resistance overall as we can use each group less frequently, and have another weapon at the ready for tough infestations.

As is always the case with science, there are other factors to consider. I think the key takeaway here is the last sentences of the paper which say that with its consistent positive performance against other baits, the researchers conclude that it is a “promising bait toxicant for the control of the German cockroach”

This is a study that will be discussed at one of our Pestworld educational sessions! Come see us in Denver and hear more about Dennis Lee's exciting new research.

Article by Ellie Sanders, BCE-Intern

References

Shao-Hung Lee, John So, Gregory S Kund, Jun-Yin Lum, Ethan Trinh, Emily L Ta, Rattanan Chungsawat, Dong-Hwan Choe, David L Cox, Michael K Rust, Chow-Yang Lee, Toxicity of isocycloseram, an isoxazoline insecticide, against laboratory and field-collected German cockroaches (Blattodea: Ectobiidae), Journal of Economic Entomology, Volume 117, Issue 3, June 2024, Pages 1086–1094, https://doi.org/10.1093/jee/toae079

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