A piece of news regarding “super mosquitoes” that I previously encountered caught my attention: a foreign infectious disease research team conducted an investigation on mosquitoes in Vietnam and Cambodia, regions where dengue fever is prevalent, and discovered that local mosquitoes have undergone mutations, rendering them immune to common pesticides. After reviewing relevant reports, we also discovered that a local mosquito species, responsible for transmitting dengue fever, jaundice, and the Zika virus, has undergone a mutation rate as high as 78%, resulting in immunity to synthetic pyrethrins, a common ingredient in insecticides. Another report highlighted that female mosquitoes of two distinct types exhibit a conscious avoidance of areas subjected to pesticide spraying after exposure to non-lethal doses of said pesticides. These reports shed light on the alarming reality that, through natural selection, mosquitoes appear to be gradually developing the ability to resist human pesticides, posing significant challenges to the prevention and control of infectious diseases.
As global climate change expands the suitable habitats for mosquitoes, diseases transmitted by these insects are garnering widespread attention and undergoing extensive research. Among the more prevalent mosquito-borne infectious diseases are dengue fever, Zika, malaria, and yellow fever. These diseases have sporadically erupted worldwide, with some countries or regions experiencing sustained outbreaks that eventually lead to endemicity.
Mosquitoes encompass a myriad of species, with approximately 3,600 identified worldwide. In my country, there exist over 370 species of mosquitoes. We can categorize mosquitoes into three major groups: Culex, Anopheles, and Aedes. The latter two groups primarily serve as vectors for disease transmission. Among them, the Aedes mosquito, commonly known as the “Asian tiger mosquito,” is capable of transmitting diseases such as dengue fever, Japanese encephalitis, and chikungunya.
Traditional methods for combating the risk of infectious disease transmission have been devised by humans throughout history. Physical methods, originating in ancient times and still employed today, have undergone advancements based on their original concepts. In ancient times, aside from utilizing herbal remedies to repel mosquitoes and alleviate the redness and swelling caused by their bites, people lacked chemical means to prevent and treat mosquito-related issues. Thus, isolation from mosquitoes became the optimal solution, leading to the creation of various forms of screen windows, screen doors, and mosquito nets. The prototype of modern-day mosquito nets can be traced back to the Three Kingdoms period. In the scorching and humid summers of Jiangdong, homemade cloth nets were used to provide airtight protection. Legend has it that Sun Quan, in search of relief from the heat, would often roll up these nets at night. In order to please Sun Quan, Mrs. Zhao painstakingly cut her hair strand by strand, braiding it into a net and adhering it with glue used for bowstrings. The resulting curtain-shaped hair net served its purpose. Additionally, exploiting insects’ phototactic behavior to trap and eliminate mosquitoes represents a common approach. With the gradual maturation of light trapping and killing technologies, an increasing variety of insect trapping light sources, such as black light lamps, high-pressure mercury lamps, and dual-wavelength lamps, have emerged. In ancient times, people were limited to using their hands to kill mosquitoes, but in modern times, electric mosquito swatters have become the norm. While physical methods are user-friendly, harmless to humans, and long-lasting, they possess the significant drawback of limited mosquito repellent efficacy.
Chemical methods have also persisted over time. Although mosquito-repellent incense was absent in ancient times, during the Zhou Dynasty, court officials employed methods such as ash sprinkling, grass burning, prayers, and sacrificial offerings to drive away mosquitoes. In the Song Dynasty, people would dry duckweed and mugwort in shaded areas during the Dragon Boat Festival, then add realgar and ignite them during the summer to repel mosquitoes. The addition of rosemary, lavender, rose scent, mint, and other aromatic spices not only serves as mosquito repellents but also enhances the olfactory ambiance of living spaces. At that time, mosquitoes plagued regions worldwide. Southeast Asians resorted to burning lemongrass to smoke their houses, while ancient Indians dried neem leaves in the shade for mosquito repellent purposes. Ancient Romans employed plants like rosemary for mosquito protection. The medical book “Ren Zhai Zhi Zhi” from the Song Dynasty details a sachet-making method: grinding orange, frankincense, clove, liquidambar resin, and aristolochia roots into a bag and wearing it on the body. It is said that this portable mosquito repellent was favored by nobles of that era.
In modern times, mosquito coils containing various chemical agents, mosquito-killing sprays, and fumigation sprays have proven effective in rapidly eliminating mosquitoes. However, they have also given rise to numerous issues. The most notable chemical agent is DDT, discovered by Swiss chemist Miller in 1939. While it plays a significant role in pest and disease control, agricultural and forestry developmentactivities, and public health, DDT has been banned or restricted in many countries due to its harmful effects on the environment and human health. This has prompted the development and use of alternative insecticides such as pyrethroids, organophosphates, and carbamates. These chemicals have varying degrees of efficacy and safety profiles.
However, the emergence of pesticide-resistant mosquitoes, as mentioned earlier, poses a major challenge to the effectiveness of chemical methods. Mosquitoes have a remarkable ability to adapt and develop resistance to insecticides through genetic mutations. This resistance can occur through various mechanisms, including target site insensitivity, increased metabolic detoxification, and reduced penetration of the insecticide into the mosquito’s body.
To address the issue of pesticide resistance, researchers and public health agencies are exploring alternative strategies for mosquito control. One approach is the use of biological control methods, such as the introduction of mosquito predators like fish or the release of genetically modified mosquitoes that can suppress mosquito populations. Another strategy involves the use of insect growth regulators, which disrupt the development of mosquito larvae and pupae.
Additionally, there is ongoing research into the development of new insecticides with novel modes of action that are less likely to encounter resistance. Scientists are also investigating the use of repellents and attractants that can manipulate mosquito behavior and reduce human-mosquito contact.
In conclusion, the development of pesticide-resistant mosquitoes poses a significant challenge to the prevention and control of mosquito-borne infectious diseases. While traditional physical and chemical methods have been employed for mosquito control throughout history, the emergence of resistance highlights the need for innovative approaches. Researchers are actively exploring alternative strategies and developing new tools to combat the growing threat of mosquito-borne diseases.