Insecticide Spraying: Overview

Introduction

Insecticides are chemicals used to kill insects (and some other arthropods, such as ticks and mites), particularly those that destroy crops, spread disease, or are otherwise considered pest species. Used in the United States since the 1860s, insecticides have been credited with helping to enable increased food production, as well as driving down rates of infectious diseases such as malaria. They are also used to help combat destructive invasive species, like the emerald ash borer. However, over time, many insecticides have been found to also have negative consequences for humans and the environment. One of the most widely used insecticides, DDT, was banned in 1972 after it was found to threaten the viability of wild birds.

Chemists have continued to develop new insecticides, often aiming for compounds that destroy target pests with minimal impact on other species. For example, the compound carbaryl (also long known by the brand name Sevin), developed in the 1950s, was hailed as less dangerous than earlier insecticides yet still highly effective, and it came into widespread use in the US. Nevertheless, many popular insecticides have continued to generate controversy. Carbaryl, for instance, has been found to have many negative health effects on humans exposed to the chemical over a long period of time (or exposed to large quantities in the short-term) and is considered a likely human carcinogen. Environmentalists have also continued to raise concerns about approved insecticides' toxicity to birds, fish, and other species—including beneficial insects. In particular, insecticides have been suspected of contributing to a known decline in pollinating bees in the United States.

Understanding the Discussion

Carbaryl: The generic name of a chemical in the class of carbamates often used as an insecticide; widely known under the brand name Sevin.

Carbamates: A class of insecticides originally developed from the calabar bean from West Africa. Carbamates are derivatives of carbamic acid. These insecticides tend to break down quickly, losing their toxic quality.

Dichloro-diphenyl-trichloroethane (DDT): A powerful organochloride compound that became a popular insecticide. The use of DDT in agriculture was banned in the US in 1972 due to the chemical's environmental impact.

Paris green: A highly poisonous powder first used in the nineteenth century as an insecticide. It was also used as a pigment to color paint and wallpaper, which explains its name.

History

People have used various substances to combat pest insects throughout history. Ancient peoples around the world discovered natural insecticide properties of various plants and other substances, such as mercury and arsenic. However, modern chemical insecticides only began to be developed in the nineteenth century. The first commercial use of chemical insecticides in the United States is believed to date from 1867, when a poisonous powder known as "Paris green" was used to kill the Colorado potato beetle, an insect that afflicted potato crops.

From the mid-1800s through the early 1900s numerous chemicals were developed and explored as insecticides. Notably, in 1939, Swiss scientist Paul Müller discovered that the chemical dichloro-diphenyl-trichloroethane (DDT) could be used to kill insects; he was awarded the Nobel Prize in Physiology or Medicine in 1948 for his discovery. DDT became extremely popular for its effectiveness in killing many different pest species. It paved the way for the development of thousands of other synthetic pesticides.

Insecticides were a boon for farmers whose crops were often diminished or even decimated by infestations of insects. The widespread use of DDT after 1942 was also credited with wiping out malaria-bearing mosquitoes and eliminating the disease from the United States. Between 1942 and 1972, an estimated 675,000 tons of DDT were used in the United States alone.

However, scientists gradually came to realize that DDT had substantial environmental consequences. Most notoriously, DDT harmed birds that ate insects sprayed with the chemical. In her 1962 book Silent Spring, Rachel Carson showed how DDT damaged the eggs of wild birds. As a result of DDT, egg shells were so thin that they often cracked before the embryos inside were able to properly mature. Continued use of the chemical, according to Carson, would result in the extinction of several bird species, and a corresponding chain reaction that would destabilize the rest of the global ecosystem. Carson and other activists also highlighted human health concerns of DDT, including cancer risk. A decade later, the US government banned the widespread use of DDT as an insecticide.

In the meantime, chemists developed new insecticides that were intended to be more selective in the insects they attacked (unlike DDT, which was an all-purpose insecticide) and to break down into nontoxic substances, avoiding degradation of the environment. Among these new compounds were carbamates, which attack insect larvae, nymphs, and adults on contact. One carbamate insecticide, carbaryl (marketed as Sevin), became one of the most widely used insecticides on the market. Carbaryl and related insecticides break down relatively quickly in the environment and consequently were considered to have much less environmental impact than earlier types.

Sevin became controversial in the 1980s amid allegations that it could result in birth defects. The use of Sevin against gypsy moths in New Jersey was feared to be linked to an increase in birth defects. In 1980, New Jersey temporarily restricted use of Sevin pending further study of this issue, but later lifted the ban. Studies of Sevin indicated it did not cause birth defects in hamsters, gerbils, guinea pigs, rabbits, sheep, and monkeys, although it was blamed for causing birth defects in dogs, but only in cases where dogs ingested many times the amount of the product that they would ordinarily encounter in areas, like lawns, where Sevin had been used.

Insecticide Spraying Today

The long-term advisability of using carbaryl has continued to be brought into question since 1980. The Environmental Protection Agency (EPA) warned in a statement issued in 1992 and revised eight years later that exposure to carbaryl by human beings could have negative effects. Illness was encountered in cases where people were exposed to large amounts of the insecticide in a short period of time, or to smaller amounts on a regular basis over a longer period of time. The EPA said that prolonged low-level exposure to carbaryl could cause headaches, memory loss, muscle weakness and cramps, and anorexia. The EPA warning said that negative effects could be reversed by discontinuing exposure. The International Occupational Safety and Health Information Centre in Europe warns that exposure to carbaryl can cause dizziness, labored breathing, nausea, unconsciousness, vomiting, muscle cramps, and excessive salivation.

Another ongoing concern has been the impact of insecticides on honeybees and some other beneficial insects, such as ladybugs. Instructions for safely using carbaryl include warnings not to spray it where bees are actively pollinating. The manufacturer of Sevin has put warning labels on the product, stating the hazards to honeybees and offering instructions for use meant to minimize the negative effects on bee populations.

Research has suggested that another class of pesticides, neonicotinoids, may be harming honeybees and wild bees alike. One study in the May 2015 issue of Nature reported that neonicotinoids were tasteless to bees but changed bees' neural patterns such that they chose to frequent plants with neonicotinoids more often than those without, a finding that they argued meant the bees could not control or prevent their pesticide exposure. Dave Goulson and his colleagues hypothesized in a March 2015 Science article that neonicotinoid exposure combined with parasites and the rotating single-crop diet of commercial honeybees might be responsible for colony collapse. In January 2016, the EPA issued a preliminary report on one neonicotinoid, imidacloprid, stating that its residues were unsafe for bees. Neonicotinoid producers contend that when properly timed and applied, their products do not harm bees.

Some question the use of all chemical pesticides and advocate instead exclusive use of “natural” pesticides derived from naturally occurring plants, or use of organic farming techniques that eliminate the use of both chemical fertilizers and pesticides or insecticides. However, other observers argue that insecticides are crucial in the fight against invasive insects, which can have devastating agricultural and environmental impacts of their own. For example, the emerald ash borer, a beetle native to Asia, was first discovered in the US in Michigan in 2002 and has gone on to kill tens of millions of trees in North America. The beetle is considered a major threat both ecologically and economically. A variety of insecticides have been used against the emerald ash borer, including emamectin benzoate, azadirachtin, and imidacloprid. All of these chemicals carry environmental concerns—leaching to shallow groundwater, for example—but have been touted as necessary to keep the emerald ash borer population under control.

In January 2016, the introduction of the mosquito-borne Zika virus to Puerto Rico and Florida from Latin America led to calls for the use of insecticide sprays. Zika has been linked to a number of birth defects—most notably, microcephaly, which causes infants to be born with smaller heads and underdeveloped brains that in turn lead to lifelong cognitive impairments. Because of this and other Zika-related complications, the Centers for Disease Control and Prevention, state health officials, and county authorities advocated the use of insecticide spraying and ground application to control mosquito populations, much as has been done against West Nile virus and dengue fever. Some proponents even argued for a DDT campaign. Environmentalists continued to argue that such widespread spraying was environmentally damaging, however, and raised concerns about direct health risks to humans as well. Moreover, the World Health Organization announced in March 2016 that the traditional spraying methods that had been conducted to stop the spread of dengue had failed to reduce disease transmission and might not work against Zika either. Epidemiologists have also warned of the risk of pest insects becoming resistant to insecticides if such chemicals are overused.

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Bibliography

Brooks, Michael. "Doesn't Kill You: Makes You Weaker." New Statesman, 10 May 2013, p. 17. EBSCOhost, . Accessed 10 Oct. 2015.

Environment

Carson, Rachel. Silent Spring. Houghton, 1962.

Connell, Des W. Basic Concepts of Environmental Chemistry, 2nd ed, CRC, 2005.

Coto, Danica. "Puerto Rico Rejects Insecticide to Fight Zika amid Protests." The Canadian Press, 22 July 2016. EBSCOhost, search.ebscohost.com/login.aspx?direct=true&db=pwh&AN=MYO340121768516&site=pov-live. Accessed 18 Oct. 2016.

"How to Read Pesticide Labels." Consumers' Research, July 1992, pp. 34+. EBSCOhost, . Accessed 15 Oct. 2015.

"Insecticides." United States Environmental Protection Agency, www.epa.gov/caddis/insecticides. Accessed 28 May 2024.

Human & Experimental Toxicology

Keaten, Jamey, and Maria Cheng. "New Ways of Fighting Zika Needed after Dengue Problems." Associated Press, 9 Mar. 2016. EBSCOhost, search.ebscohost.com/login.aspx?direct=true&db=pwh&AN=APd909f622dcfd4b17bdd1e60decdee63b&site=pov-live. Accessed 18 Oct. 2016.

Livingston, Edward H. "Safety of Aerial Pesticide Spraying for Mosquitoes." JAMA, vol. 310, no. 3, 2013, p. 333. . Accessed 15 Oct. 2015.

Morris, Alex. "The Bee Killers." Rolling Stone, 27 Aug. 2015, pp. 50+. EBSCOhost, Accessed 28 Oct. 2015.

Pease, Craig M. "A Tale of Pesticides Then and Now." Environmental Forum, vol. 28, no. 2, 2011, p. 18. EBSCOhost, . Accessed 15 Oct. 2015.

Ranii, David. "EPA Study Adds Fuel to Insecticide Controversy." The News & Observer, 12 Jan. 2016. , search.ebscohost.com/login.aspx?direct=true&db=pwh&AN=2W6234606011&site=pov-live. Accessed 18 Oct. 2016.

Snyder Sachs, Jessica. "Poisoning the Imperiled." National Wildlife, Dec. 2003–Jan. 2004, World ed., pp. 22+. EBSCOhost, . Accessed 15 Oct. 2015.

Terrell, Rebecca. "Zika Prompts Pleas for DDT." New American, vol. 32, no. 5, 2016, p. 22. EBSCOhost, search.ebscohost.com/login.aspx?direct=true&db=pwh&AN=113612190&site=pov-live. Accessed 18 Oct. 2016.

Thomsen, Edward K., et al. "Underpinning Sustainable Vector Control through Informed Insecticide Resistance Management." PLoS ONE, vol. 9, no. 6, 2014. EBSCOhost, . Accessed 28 Oct. 2015.

Timbrell, John. The Poison Paradox: Chemicals as Friends and Foes. Oxford UP, 2005.

Yu, Simon J. The Toxicology and Biochemistry of Insecticides, 2nd ed., CRC, 2015.