According to a study from the Journal of Medical Entomology, bed bugs have developed a resistance to neonicotinoidss. Neonicotinoids, or neonics, are the most commonly used insecticide to fight the already elusive and resilient bed bugs.

Authors of the study discovered the resistance by collecting bed bugs from human dwellings in Cincinnati and Michigan and exposing them to four different neonics: acetamiprid, dinotefuran, imidacloprid and thiamethoxam.

The same neonics were applied to a bed bug colony that had not had exposure to insecticide for 30 years, as well as to a pyrethroid-resistant population from New Jersey that had not been exposed to neonics since 2008. The initial colony of bed bugs died after exposure to small amounts of neonics. The New Jersey bed bugs died when exposed to imidacloprid and thiamethoxam but resisted the other two neonics.

According to researchers, the neonic resistance in the New Jersey bed bugs could be credited to pre-existing resistance mechanisms. Bed bugs produce “detoxifying enzymes” to counter exposure to insecticides, and the researchers found that the New Jersey bed bugs had higher levels of the enzymes than did the initial colony of bed bugs.

The bed bugs collected from Cincinnati and Michigan proved to be tougher, with a much higher resistance to neonics than the other two sites sampled. When compared with the initial colony mentioned above, the Michigan creatures were 462 times more resistant to imidacloprid, 198 times more resistant to dinotefuran, 546 times more resistant to thiamethoxam and 33,333 times more resistant to acetamiprid. Similarly, the Cincinnati bed bugs were 163 times more resistant to imidacloprid, 358 times more resistant to dinotefuran, 226 times more resistant to thiamethoxam and 33,333 times more resistant to acetamiprid.

Following the findings, researchers warn pest control professionals on what they use to fight bed bugs. It’s recommended that they be vigilant and watch for declining performance of products that contain neonicotinoids.