As the year 2013 reaches its wintry close, scientific studies about global warming and other climate changes continue to warn us of the growing seriousness of the environmental crisis. The amount of carbon dioxide in the air reached another record. On May 10, the atmospheric recording station on Hawaii’s Mauna Loa volcano reported that for the first time ever, carbon dioxide in the atmosphere was recorded at 400 parts per million (ppm), significantly higher than 350 ppm considered by some scientists to be the uppermost safe level for that greenhouse gas (1). But a greater concern is the increase of methane in the atmosphere, especially in Arctic regions. In November, a University of Alaska Fairbanks study concluded that atmospheric concentrations of methane are much higher than previously reported. Methane “is as much as thirty times” stronger than carbon dioxide at aggravating the greenhouse effect that is heating the planet (2). Many lay folk recognize methane as a flammable gas that is also a main ingredient in flatulence. Needless to say, no one should want any more methane in the atmosphere.

While the Arctic ice cap melts, global warming affects Africa in a troubling manner that could eventually affect mosquito control as far away as the United States. On July 16, 2013, Public Radio International reported that mosquitoes, the insects that kill more humans than AIDS, automobiles or guns, are rapidly developing resistance against pyrethroids, the synthetic chemical pesticides that are widely used in the United States to combat the deadly pests (3). (It should be remembered that resistance and immunity are not always synonymous; resistance means that an individual can resist but not necessarily effectively. Immunity means that the resistance has become so developed that it is almost always effective.). Mosquitoes of the Anopheles genus (group of species) that spread malaria have been the target of a massive worldwide aid campaign to reduce the disease by providing millions of bed nets permeated with pyrethroids. In Africa and other malaria stricken regions, bed nets have served as a first line of defense against mosquitoes, saving hundreds of thousands of lives since they were widely introduced in the 1990s (4, 5). Here in America, pyrethroids are usually the last line of defense, being sprayed from trucks or even planes after all other methods have either failed – or in some cases – not been tried.

In the chemical warfare against mosquitoes, the insects long ago developed resistance against DDT. And the news that African mosquitoes are developing resistance against pyrethroid insecticides will affect pest control in the US and other nations in several ways.

In Africa and other regions, pyrethroid treated bed nets are used to protect sleeping people from mosquitoes. For over 20 years, the bed nets have worked effectively, reducing malaria and other deadly mosquito borne diseases such as West Nile Virus (WNV), dengue, and yellow fever. However, in recent years, researchers have discovered an accelerating development of resistance by mosquitoes. When the bed nets were first introduced, some prominent entomologists such as Janet Hemingway of England’s prestigious Liverpool School of Tropical Medicine cautioned against applying only one type of pesticide to the nets. They warned that relying only on one type would give mosquitoes a better chance to develop resistance (3). These warnings went unheeded.

Until the news that mosquitoes are developing resistance against pyrethroid insecticides, the bed net campaign was probably the most hopeful sign in the battle against malaria. In addition to saving so many human lives, the growing success against malaria means that the savings of those lives helps nations devote more people and resources to other problems. Many forms of infrastructure that people in developed nations take for granted such as roads, sanitation, communication, primary education, and basic health become extremely difficult projects in poorer societies because of the human and economic toll taken by diseases, especially malaria. Recent success in the battle against malaria has allowed Africa and other developing areas to begin and expand infrastructure projects. If malaria and other mosquito borne diseases rebound, this real progress could stall (6).

In North America, the pyrethroids commonly used in Africa are usually the last resort in Integrated Pest Management (IPM) mosquito control and accordingly are not used as much (7). For this reason, the chance that North American mosquitoes will develop resistance to pyrethroids is decreased. Nevertheless, the fact that many African mosquitoes are developing such a resistance is a warning and a reminder. We are warned that excessive reliance on synthetic chemical pesticides will only buy time while possibly threatening our health and environment. And we are reminded that IPM remains the safest and ultimately most effective method of pest control.

Although the threat that North American mosquitoes will develop resistance against pyrethroids is probably not an immediate one, it can not be summarily discounted. Climate change, especially warming trends, show that many pests once confined to the tropics are now marching inexorably into temperate lands. Hotter summers, milder winters, more storms, longer growth seasons, and other effects of climate change all help invasive species to advance into new territories. Pests become active earlier in the year and increase their populations and ranges (8). A recent infamous example is the Asian tiger mosquito (Aedes albopictus). This deadly insect which can carry yellow fever, dengue, WNV, and other diseases reached American shores in a shipment of used tires in 1985. From their initial landing in Houston, Texas, they have spread all over the eastern USA (9). In this century they have become established in Southern California and are moving north toward the San Francisco Bay Area (10, 11).

Other pests that are moving into new territory include fire ants and deer ticks. The latter transmit Lyme disease and similar debilitating illnesses (8). Climate change is also causing mutations in the pathogens that cause diseases, creating new and resistant forms of these sicknesses. Warmer weather can also speed up the incubation period of disease pathogens such as Plasmodium, the protozoa that cause malaria (12).

Over 1600 years ago, St. Basil the Great blamed unsustainable greed for a drought and famine that crippled what is now eastern Turkey (13). Most versions of the worldwide story of the Great Flood also blame human activity for that environmental disaster (14). The invasions of Asian tiger mosquitoes and other pests show again that our activities can certainly accelerate the immediate effects of climate change even as some interests continue to insist that we don’t help cause it.

The fact that global warming has allowed different species of mosquitoes and other pests to migrate into temperate zones coupled with the other fact that many insects are developing resistance against pesticides means that we face a potential health crisis from the diseases they carry. And these two phenomena – northward migration of tropical mosquitoes and increasing resistance against pesticides – reinforce each other in a warming environment. This is because mosquitoes mature faster in hot weather. Because they reach adulthood sooner, generations of mosquitoes are reproduced faster and at increased rate (12). As a result, they breed more generations and with time, the newer generations can develop resistances against pesticides. And because climate change can facilitate the expansion of pests into new lands, it means that such pests can also bring their resistance to pesticides with them.

These circumstances show greater need for IPM methods to prevent invasive pests from establishing themselves in new areas and from developing resistance. Whereas chemical pesticides often lose efficacy, IPM, with its emphasis on prevention and multiple methods, can be effective for as long as necessary. And when pesticides are used in IPM, they are likely to remain effective as they are used less indiscriminately.

by Howard Williams, Veteran Mosquito Biker

Sources

1. British Broadcasting Corporation on May 10, 2013 as reported in the Wikipedia entry for “Carbon dioxide in the atmosphere” and Detroit Free Press, November 6, 2013 as reported on that newpaper’s website.
2. Fairbanks (Alaska) News Miner, November 27, 2013 as reported on that newpaper’s website.
3. Public Radio International website: pri.org
4. Centers for Disease Control website:
   www.cdc.gov/malaria/malaria_worldwide/reduction/itn.html
5. “Technologies for global health” The Lancet 2012 in Wikipedia entry for “Malaria”
6. Wikipedia entry for “Malaria”
7. Environmental Protection Agency website:
   www.epa.gov/opp00001/factsheets/ipm.htm
8. World Wildlife Fund website: www.wwfblogs.org/climate/content/spread-disease-pests-climate-change
9. Ohio State University study “Asian Tiger mosquito” as reported in Wikipedia entry “Aedes albopictus”
10. University of California, Riverside Center for Invasive Species Research website:
    cisr.ucr.edu/asian_tiger_mosquito.html
11. Cupertino Patch, April 27, 2012 as reported on that newspaper’s website
12. “Global Warming and Malaria” by Natalie Van Hoose, plaza.ufl.edu/inkling/mosquito-borne_diseases.html
13. St. Basil the Great, Sermon “In Time of Famine and Drought”
14. Genesis, Chapters 6 through 9