02
Aug
The Growing Insecticide Resistance Issue Increases Concerns Over Deadly Disease Transmission Through Mosquitos
(Beyond Pesticides, August 2, 2023) A study published in Pest Management Science finds resistance to insecticides like pyrethroids are challenging attempts to control the mosquito Aedes aegypti (Ae. aegypti), the primary transmitter (vector) of dengue fever. While this study takes place in Bangladesh, resistance to biocides—whether to antibiotics, antimicrobials, or pesticides—is growing globally. Prevention of disease outbreaks is threatened by reliance on chemical biocides to which pathogens and their vectors develop resistance. In fact, resistance is predicted by elementary population genetics, and the speed of its evolution is directly related to the toxicity—that is, the strength of selection pressure—and inversely related to the generation length of the organism. (See PAY articles here and here, a PBS article here.)
Insecticide resistance has been an issue since the introduction of DDT (dichlorodiphenyltrichloroethane) in the 1940s. Although most countries currently ban DDT use, the compound is not the only chemical pesticide promoting pest resistance. Several current-use insecticides pose the same threat. Areawide, indiscriminate spraying of insecticides is causing resistance to develop among many pests. Mosquitoes have become increasingly resistant to synthetic pyrethroids, in addition to other classes of insecticides, such as carbamates and organophosphates. Thus, this study demonstrates the need for sustainable and practical strategies to combat the growing disease burdens.
The study notes, “Intensive use of pyrethroids in Dhaka has selected for highly resistant mosquito populations, which was confirmed through bioassays. This pyrethroid resistance is associated with high frequencies of the V1016G kdr mutation and activities of detoxifying enzymes. As evidenced from our free-flight experiments, the effective operational use of pyrethroids in control programs is compromised and, therefore, requires reconsideration. […] Ultimately, scalable and sustainable non-insecticide-based approaches such as Wolbachia-based population replacement could have an important role in curbing Aedes-borne diseases in Bangladesh.”
Researchers from the QIMR Berghofer Medical Research Institute, Australia, examined the common insecticides used in Dhaka, Bangladesh, to determine the mechanisms and intensity of insecticide application driving resistance. The pyrethroid insecticides tested include permethrin and deltamethrin. Using a bottle assay, the research measures the mortality percentage of mosquitos after insecticide exposure. The study finds Ae. Aegypti mosquito colonies display significantly higher levels (high-intensity) of resistance to pyrethroids. Although the mortality rate of mosquitos exposed to permethrin is much lower than deltamethrin (2–24% mortality and 48–94% mortality, respectively), the metabolic mechanisms involved are the same. Specifically, responses to the synergistic reaction between pyrethroids induce multi-function oxidases, esterases, and glutathione S-transferases. Moreover, a high frequency of kdr alleles for resistance indicates a V1016G mutation, conferring resistance to deltamethrin. Although exposure can mitigate host-seeking behavior, this effect is only temporary. Considering over 74 percent of mosquitos from colonies in Dhaka survive initial exposure to pyrethroids, the implication for increased disease prevalence is elevated.
Associate Professor Gregor Devine, Ph.D., at the Mosquito Control Laboratory, said, “‘The use of pyrethroids in Dhaka is no longer effective, and the control program needs to switch to a different approach.’ The study suggests the presence of high levels of insecticide resistance among Ae. aegypti populations may have contributed to the escalating dengue burden.”
This study resembles an all too familiar phenomenon of resistance among pest populations. Scientists note resistance is an entirely normal, adaptive phenomenon: organisms evolve, “exploiting” beneficial genetic mutations that give them a survival advantage. However, resistance is growing in all sectors of pest control, including critically needed agriculture and medicine. For nearly a century, the human response to resistance is the development of a compound that kills the resistant organism (whether pest or weed or bacterium or fungus), which works for a while. However, the dependence on chemical solutions is increasingly failing. Whether it is antibiotics for bacterial infections, herbicides for weeds/pests, or insecticides to mitigate vector-borne diseases, organisms are becoming resistant to usually toxic compounds. Once an organism inevitably becomes resistant to a particular chemical control strategy, people —the chemical industry, researchers, applicators, farmers, public health workers, clinicians, et al.—will have typically moved on to the subsequent chemical “solution.” Pesticide Action Network North America (PANNA) notes, “The World Health Organization underscored the problem in their 2012 guidance on policymaking for Integrated Vector Management (IVM): ‘Resistance to insecticides is an increasing problem in vector control because of the reliance on chemical control and expanding operations…Furthermore, the chemical insecticides used can have adverse effects on health and the environment.’”
Beyond Pesticides has written extensively on the issue of resistance, particularly the relationship to the use of agricultural and other land management pesticides, with the central message: resistance is a symptom of the ineffectiveness of chemical-intensive agriculture and leads to increased use of more and more toxic pesticides. In addition, resistance in one of the “sectors” mentioned above can “crossover” to become problematic in another. Growing pesticide resistance often leads to an increase in chemical inputs to control pests. Exposure to permethrin already has implications for human health, including cancer, endocrine (hormone) disruption, reproductive dysfunction, neurotoxicity, and kidney/liver damage. Mosquito resistance can augment the use of chemical control methods, including the addition of toxic synergists like piperonyl butoxide (PBO), known to cause and exacerbate adverse health effects from exposure. Therefore, researchers need to understand the mechanisms prompting pesticide resistance among mosquito populations to safeguard human health from disease.
The use of permethrin and deltamethrin through fogging and ariel application plays a significant role in the high intensity of resistance among the Ae. aegypti colonies from Dhaka. The study highlights that pyrethroids act on the nervous system of insects, using a “knockdown” effect to cause death. Although this study suggests mosquitos can recover from the knockdown (KD) effect via a mutation in the kdr alleles, this KD effect is dose-dependent. Thus, pyrethroid increases the frequency of kdr mutation to prompt resistance. The study highlights, “[…] the substantial recovery seen after KD suggests poor binding of the pyrethroid to the mutated VGSC and a key role for metabolic mechanisms in ‘mopping up’ the pyrethroids.”
This study is not the first to demonstrate resistance to metabolic mechanisms driving genetic resistance among mosquito populations. A Colorado State University study finds two types of pyrethroid resistance: VGSC and detoxification metabolism. Similar to this study, the Colorado researchers suggest mosquitos that recover from the initial insecticide knockdown contribute to resistance in the field. Sublethal exposure may be responsible for the mosquito’s ability to recover. Rather than dying from dehydration and predation, recovery mechanisms allow mosquitoes to develop resistance over time. This study enables researchers to fully understand the genetic differences between mosquitos that exhibit resistance and those who recover or die. Knowing how genes factor into pesticide metabolism can help researchers understand how resistance evolves under field-realistic conditions. Therefore, it is essential to understand insect behavior that propagates vector-borne disease transmission that exacerbates the widespread public health crisis. Previous studies associate memory and associative learning with behavioral changes occurring in response to chemical exposure.
In the context of deadly pesticide use in developing countries, Jay Feldman, executive director of Beyond Pesticides, has noted, “We should be advocating for a just world where we no longer treat poverty and development with poisonous band-aids but join together to address the root causes of insect-borne disease because the chemical-dependent alternatives are ultimately deadly for everyone.” He also said, “We should focus on the deplorable living conditions and inequitable distribution of wealth and resources worldwide that give rise to squalor, inhumane living conditions, and the poor state of development that, together, breed insect-borne diseases like malaria.”
Even if dengue is not a local concern, there remains general concern surrounding the diseases mosquitoes can transmit, including the West Nile and Zika viruses. Beyond Pesticides provides valuable information on mosquito management and insect-borne diseases in the Mosquito Management and Insect-Borne Diseases section devoted to these issues. Furthermore, keep up on pesticide-related science and news, including mosquitoes and pesticide resistance, on Beyond Pesticides’ Daily News blog.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Pest Management Science, Phsy.org
Pesticides, insecticides, pollution, dirty air and water, stress of living under the demands of a society not working for the betterment of people, and much more, is not good for our health. These potions are killing us and the bees, and the birds, and animals, insects and the planet. The people don’t deserve this.The only ones profiting are those causing the damage. Corporations, industry, Citizen”s United, dark money, MAGA opinions and dictates, all are harming and not helping people. Even the increase in wages to $17 per hour is against the GOP yet the GOP intend to have an $8,000.00 increase. What’s fair or right snout that? Nothing. As with all pesticides, etc … noting is right, just for money. and the hell with people or other living things. Beyond sad.
August 2nd, 2023 at 7:03 pm