Research from the University of Kentucky:
Bed bugs evolved unique adaptive strategy to resist pyrethroid insecticides Fang Zhu, Hemant Gujar, Jennifer R. Gordon, Kenneth F. Haynes, Michael F. Potter & Subba R. Palli
Department of Entomology, College of Agriculture, University of Kentucky, Lexington, KY 40546, USA.
Recent advances in genomic and post-genomic technologies have facilitated a genome-wide analysis of the insecticide resistance-associated genes in insects. Through bed bug, Cimex lectularius transcriptome analysis, we identified 14 molecular markers associated with pyrethroid resistance. Our studies revealed that most of the resistance-associated genes functioning in diverse mechanisms are expressed in the epidermal layer of the integument, which could prevent or slow down the toxin from reaching the target sites on nerve cells, where an additional layer of resistance (kdr) is possible. This strategy evolved in bed bugs is based on their unique morphological, physiological and behavioral characteristics and has not been reported in any other insect species. RNA interference-aided knockdown of resistance associated genes showed the relative contribution of each mechanism towards overall resistance development. Understanding the complexity of adaptive strategies employed by bed bugs will help in designing the most effective and sustainable bed bug
Insecticide resistance is considered to be a condensed model of natural selection. The extensive use of insecticides accelerated the accumulation of resistance related factors in survivors. Therefore, studies on the molecular basis of these adaptive traits are of theoretical and applied importance in understanding the evolution of insecticide resistance and devising the most effective and sustainable resistance management tactics. The physiological and biochemical mechanisms of insecticide resistance may evolve along several trajectories 2,3.
When insects come in contact with or consume insecticides, they may develop resistance by modification in the insect cuticle or digestive tract linings that prevent or reduce the rate of penetration (termed reduced penetration) 4. Once insecticide enters the organism, enhanced metabolic detoxification could decrease the concentration of insecticides before they reach the target site
2,4 . In some instances, the insecticide may be excreted from the organism at an accelerated rate in resistant populations 5. Resistant insects may also evolve target site insensitivity mechanisms which reduce or eliminate the binding affinity of insecticides to their target proteins 3,6.
Additionally, behavioral resistance helps to avoid the lethal effects of insecticides through behaviors that reduce exposure 3,4 . A common phenomenon of insecticide resistance is that multiple mechanisms operate simultaneously in resistant insects such as the house fly 7–9, mosquito
10–13 , cockroach 14 , and cotton bollworm 15.
Typically, a combination of diverse mechanisms provides significantly higher levels of resistance than one individual mechanism 4. Pyrethroid insecticides are the mainstay for bed bug control due to their safety, effectiveness, longevity of their residual activity and low cost. However, ubiquitous development of resistance to pyrethroids and the fact that pyrethroid resistance generally confers cross-resistance to other insecticides make bed bug management a difficult task 16. Recent advances in insect genomics and development of post-genomic technologies have facilitated a genome wide analysis of the resistance associated genes in many medically or agriculturally important
insect species 17–20 . In the current study, molecular markers related to pyrethroid resistance were identified based on thorough transcriptome analysis. The identified markers were then used to examine the contribution of different resistance mechanisms in 21 field-collected bed bug populations. Interestingly, bed bugs express most of their pyrethroid resistance associated genes in the integument which serves as the first cellular barrier for pyrethroids to cross before reaching target sites. RNA interference-aided knockdown in the expression of genes coding for proteins involved in mechanisms of pyrethroid resistance in the insecticide-resistant bed bugs showed relative contribution of each mechanism towards overall resistance.
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