(Beyond Pesticides, January 5, 2022) The use of insecticidal bed nets (IBNs) to prevent mosquito bites in malaria-endemic communities may lead to the development of resistance in secondary pests such as bed bugs, according to a study published in Parasites and Vectors. Reduced effectiveness against bed bugs and other non-mosquito pests can lead to the abuse of both mosquito adulticides and bed nets, and hamper efforts to stop the spread of malaria and other insect-borne diseases. Because resistance follows a predictable pattern in both disease-carrying and secondary pests, there is a critical need for safer, non-chemical solutions, including ecological and structural approaches to pest management.
Researchers examined the effectiveness of untreated bed nets along with those treated with the commonly used synthetic pyrethroids deltamethrin and permethrin against a population of insecticide-susceptible and pyrethroid-resistant bed bugs. Insecticidal nets were fixed between two glass vessels in both an aggregation and a blood meal experiment. For the aggregation experiment, fully fed bed bugs were set up to traverse the mosquito net to reach a darker resting place. In the blood meal experiment, unfed bed bugs were set up, which crossed the web to obtain a blood meal.
Both experiments show that the mosquito nets have little deterrent effect on either insecticide-sensitive or pyrethroid-resistant bed bugs. In fact, in the aggregation experiment, insecticide-susceptible bed bugs performed slightly better than resistant strains, with 100% of them being collected in the aggregation vessel at the end of the experiment. They were able to successfully pass both untreated and permethrin-treated nets, while approximately 80% of susceptible bed bugs were able to pass deltamethrin-treated nets. Researchers point out that many resistant beetles were unable to cross the mosquito nets, resulting in less than perfect aggregation numbers at the end of the experiment. Approximately 30% of resistant bed bugs did not make it through the untreated mesh, while over 90% were able to pass deltamethrin and permethrin.
For the blood meal experiment, bed bugs were able to pass through the untreated nets, with permethrin treatment achieving similar results and deltamethrin only slightly reducing the number of successful blood meals. Researchers note that maneuverability likely changes depending 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 effectiveness.
After passing through the insecticide-treated net, only susceptible bed bug strains showed mortality, with approximately 2% being killed by permethrin and an average of 64% by deltamethrin. No bed bugs from the resistant population were killed.
The researchers argue that bednet pyrethroid exposure likely exacerbates resistance in bedbugs more than in target mosquitoes. This is indicated because all life stages of bed bugs are exposed, while only adults are exposed to bed nets for mosquitoes. Mosquitoes can also be repelled before they actually settle on a mosquito net, while bed bugs can have prolonged contact by walking over the net in search of an opening. Researchers also argue that while mosquitoes are short-lived and can fly away, bed bugs stay indoors and live comparatively much longer. Finally, the researchers note that the bed bug’s biology and ecology inherently leads to faster resistance. While bed bugs are highly inbred, resulting in rapid exchange of resistance genes, mosquitoes in outdoor populations have a broad genetic pool that is comparatively slow in developing resistance. A
About a decade ago, similar research found evidence not only that insecticidal nets promote resistance to bed bugs, but that this resistance has spread to other parts of the world. While bed bugs prefer to stay where they are, human commerce isn’t nearly as static. “When bed bugs emerge from local sanctuaries like poultry farms, one would expect the bed bugs to be genetically very similar,” explained entomologist Coby Schal, PhD of North Carolina State University. „We didn’t find that.“
“The obvious answer is in the tropics, where they used treated mosquito nets [and] high levels of insecticides on clothing and bedding to protect the military,” said Warren Booth, PhD, also of 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. In combating bed bugs and mosquitoes, pest infestations and disease spread are often just a symptom resulting from a variety of economic inequalities, and it is the lack of good public sanitation and infrastructure that gives disease-carrying insects a foothold for infecting the community Offer. A 2021 study confirms this, showing that the prevalence of disease-carrying mosquitoes is much higher in urban areas with lower socioeconomic 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 solutions continue to show their lack of staying power. See mosquito management and insect-borne diseases.
All unattributed positions and opinions in this article are those of Beyond Pesticides.
Source: Parasites and Vectors
