Jim Ballard, PhD, discusses how the development of resistance is the ability to tolerate larger and larger doses of an insecticide within a strain of insects. A good summary of this concept and how it works may be found in Pest Control Technology magazine published in Oct of 2013.
Earlier this year, a scientific report was published that indicated some bed bug field populations were found to have a level of resistance to a new class of insecticidal active ingredients, the neonicotinoids, used in the control of bed bug populations. Some examples of neonicotinoids include: acetamiprid, imidacloprid, dinotefuran, and thiamethoxam.
Typically, these neonicotinoids are not used alone as an insecticide. Most are paired with another active ingredient to result in an insecticide that kills bed bugs by using two modes of action (to slow resistance development). Most of the pairings are with synthetic pyrethroid active ingredients. This study centered upon testing three strains of bed bugs captured in the field and tested in the laboratory. After applying a droplet of each test neonicotinoid to test bed bugs, one strain was found to have moderate resistance while two other strains exhibited moderate to high levels of resistance.
How an insecticide is formulated is critical in it’s performance under field conditions. Insecticides formulated as a wettable powder, for instance, are usually far more effective that those formulated dissolved in a liquid (e.g., emulsified or suspensions) because of the ease of pickup of the wettable powder by the insect. As we learn more about how neonicotinoids and the combinations of neonicotinoids with other active ingredients influence the development of resistance in bed bugs, it will become clearer to predict the fate of these combination products under field use conditions.
One example of how a formulation can influence insecticide performance would include the exposure of bed bugs to fabric impregnated with the synthetic pyrethroid permethrin. Because of the unique way the permethrin is formulated on the fabric (ActiveGuard® Mattress Liners), a ten-minute exposure of bed bugs to the fabric results in significantly reduced feeding and egg laying. This is because a ten-minute exposure to the fabric results in a large amount of permethrin penetrating past the cuticle (outer skin) into the bed bug causing neurological changes that interfere with feeding, which usually leads ultimately to death.