(Beyond Pesticides, January 5, 2022) The use of insecticidal bed nets (IBNs) to prevent mosquito bites in malaria-endemic communities can result in resistance developing in secondary pests like bed bugs, according to research published in Parasites and Vectors. Decreased efficacy against bed bugs and other non-mosquito pests may result in misuse of both mosquito adulticides and bed nets, hampering efforts to stop the spread of malaria and other insect-borne disease. With resistance following a predicable pattern in both disease-transmitting and secondary pests, there is a critical need to embrace safer, nonchemical solutions, including both ecological and structural approaches to pest management.
Researchers investigated the efficacy of untreated bed nets along with those treated with the commonly used synthetic pyrethroids deltamethrin and permethrin against both a population of insecticide-susceptible and pyrethroid resistant bed bugs. Insecticidal netting was secured between two glass jars in both an aggregation and blood meal experiment. For the aggregation experiment, fully fed bed bugs were set up to cross through the bed net to reach a darker resting location. With the blood meal experiment, unfed bed bugs were set up to cross the netting to receive a blood meal.
Both experiments show the bed nets carrying little deterrent power to either insecticide-susceptible or pyrethroid-resistant bed bugs. In the aggregation experiment, insecticide-susceptible bed bugs in fact fared slightly better than resistant strains with 100% of them being collected in the aggregation jar at the end of the experiment. They were able to successfully pass through both untreated and permethrin-treated nets, while roughly 80% of susceptible bed bugs were able to pass through deltamethrin-treated nets. Researchers indicate that many resistant bugs failed to cross the bed nets, resulting in less than perfect aggregation numbers at the end of the experiment. Roughly 30% of resistant bed bugs did not make it through the untreated net, while over 90% were able to pass through deltamethrin and permethrin.
For the blood meal experiment, bed bugs were able to pass through the untreated nets with the permethrin treatment marking similar results, and deltamethrin only slightly decreasing the number of successful blood meals. Researchers indicate that maneuverability likely changes based on whether the bed bug has successfully fed, and that the size of the holes in the mosquito nets tested also likely played an important role in efficacy.
After passing through the insecticide-treated netting, only susceptible bed bug strains showed any mortality, with roughly 2% killed from permethrin and an average of 64% from deltamethrin. No bed bugs from the resistant population were killed.
The researchers argue that bed net pyrethroid exposure likely exacerbates resistance in bed bugs more than target mosquitoes. This is indicated because all life stages of bed bug are exposed, while with mosquitoes, only the adults come into contact with bed nets. Mosquitoes may also be repelled before actually settling on a bed net, while bed bugs may have prolonged contact by walking over the netting in search of an opening. Researchers also argue that while mosquitoes are short-lived and can fly away, bed bugs remain in the home and live much longer lives comparably. Lastly, researchers note that the bed bugâ€™s biology and ecology inherently leads to a faster resistance. While bed bugs are highly inbred, leading to rapid exchange of resistance genes, mosquitoes have broad genetic pools in outdoor populations that in comparison slows the development of resistance. Â
Roughly a decade ago, similar research not only found evidence that insecticidal nets are fueling bed bug resistance, but that this resistance was making its way to other parts of the world. While bed bugs prefer to stay where they are, human commerce is not nearly as static. â€śIf bed-bugs emerged from local refugia, such as poultry farms, you would expect the bed-bugs to be genetically very similar to each other,â€ť explained entomologist Coby Schal, PhD from North Carolina State University. â€śThis isnâ€™t what we found.â€ť
â€śThe obvious answer is the tropics, where they have used treated bed nets [and] high levels of insecticides on clothing and bedding to protect the military,â€ť said Warren Booth, PhD, also from North Caroline State University.
As Beyond Pesticides has repeatedly reported, the best solution to eliminating pesticide resistance is to stop using the chemical in the first place. With bed bugs and mosquito management, pest infestations and disease spread are often only one symptom resulting from a broad range of economic inequalities, and it is lack of good public sanitation and infrastructure that provides disease-carrying insects footholds for community infection. A 2021 study backs this up, showing the prevalence of disease carrying mosquitoes to be much higher in urban areas of lower socio-economic conditions.
Safer, ecologically based approaches to mosquito and bed bug management are needed to successfully prevent disease in the long term, as short-term chemical fixes continue to show their lack of staying power. See Mosquito Management and Insect-Borne Diseases.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Parasites and Vectors