After 50 Years, Scientists Still Not Sure How DEET Works

DEET (short for N,N-diethyl-meta-toluamide) is the most widely used insect repellent in the world for a very good reason – it works really, really well! Just a quick spray on exposed skin keeps mosquitoes, flies, fleas, chiggers, and ticks away. Developed by scientists at the U.S. Department of Agriculture and patented by the U.S. Army in 1946, millions of people worldwide use DEET to ward off vector-borne diseases. First of all, why would researchers study DEET if it works so well? While DEET is an effective repellent, it doesn’t work against all bugs, it’s corrosive to plastics and there are concerns about its effect on human health.

 

Structural Formula for N, N-diethyl-meta-toluamide (DEET).
Courtesy of Wikipedia – Click on the image for a larger version.

How DEET actually works has puzzled scientists for more than 50 years. Scientists long surmised that DEET masks the smell of the host, or jams or corrupts the insect’s senses, interfering with its ability to locate a host. Mosquitoes and other blood-feeding insects find their hosts by body heat, skin odors, carbon dioxide (breath), or visual stimuli.

Amazingly, within a few months this year, scientists from two different labs have come up with competing explanations of how DEET works. In March of 2008, researchers at Rockefeller University in New York, said that DEET jams odorant receptors in insect nervous systems, in effect masking odors that would ordinarily attract the bugs. According to Dr. Leslie B. Vosshall, a researcher who worked on the project, now that they know that DEET targets OR83b co-receptors, they can quickly screen thousands of other compounds in hope of finding one that is even more effective and has fewer disadvantages.

Are you sure, ask researchers at the University of California, Davis? Mosquitoes flee because of their intense dislike for the smell of the chemical repellent and not because DEET jams their sense of smell. In August 2008, in a paper published in The Proceedings of the National Academy of Sciences, they provide a simpler explanation. Mosquitoes, they say, smell DEET directly and avoid it.

Dr. Vosshall, involved in the earlier study, said that her team stood by its work, and that its findings were based on a variety of experiments. So for now, the jury is still out.

Connecting to the National Science Education Standards

These competing explanations on how DEET works provides a perfect example of one aspect of the nature of science – Scientific Claims are Subject to Peer Review and Replication. Researchers in labs across the world work on answering many of the same questions. The results of their work are published in peer reviewed journals so that researchers around the world can examine their data and logic, identify alternative explanations, and replicate observations and experiments. Peer review is an integral part of genuine scientific enterprise and goes on continuously in all areas of science.

The National Science Education Standards in the History and Nature of Science Content Standard G describes what middle school students should understand about this part of the nature of science, including:

It is normal for scientists to differ with one another about the interpretation of the evidence or theory being considered.

Different scientists might publish conflicting experimental results or might draw different conclusions from the same data.

It is part of scientific inquiry to evaluate the results of scientific investigations, experiments, observations, theoretical models, and the explanations proposed by other scientists.

Although scientists may disagree about explanations of phenomena, about interpretations of data, or about the value of rival theories, they do agree that questioning, response to criticism, and open communication are integral to the process of science.

Additional Resources

Read the entire National Science Education Standards online for free or register to download the free PDF. The content standards are found in Chapter 6.

Science For All Americans Online: The Nature of Science
Science for All Americans consists of a set of recommendations on what understandings and ways of thinking are essential for all citizens in a world shaped by science and technology.

Household Product Database
List of products that contain DEET.

Chemical Technical Summary for Public Health and Public Safety Professionals
The Department of Health and Human Services provides a summary of all medical cases and research done on DEET.

We Want Your Feedback

We want and need your ideas, suggestions, and observations. What would you like to know more about? What questions have your students asked? We invite you to share with us and other readers by posting your comments. Please check back often for our newest posts or download the RSS feed for this blog. Let us know what you think and tell us how we can serve you better. We appreciate your feedback on all of our Middle School Portal 2 publications. You can also email us at msp@msteacher.org.

This post was originally written by Kimberly Lightle and published August 26, 2008 in the Connecting News to the National Science Education Standards blog. The post was updated 4/19/12 by Jessica Fries-Gaither.

Pandemics and Their Numbers

Everywhere our students are hearing about the HINI influenza. Their interest offers an opportunity to co-teach with a science teacher in an investigation of what we know and don’t know about this pandemic. The New York Times has created an interdisciplinary lesson Pandemic Panic: Researching the 2009 Influenza A (H1N1) Pandemic that asks students to inquire into the current influenza as advisers from multiple perspectives and to share factual information they learn with their classmates and school communities.

The lesson opens with students considering “what we know” and “what we want to know.” The investigation begins as student groups take on such roles as “health advisers” or “economic advisers” or “historical advisers.” “Statistics advisers” could be added, in my opinion. What do the numbers tell us? FluView from the CDC 2008-2009 Influenza Season Week 38 ending September 26, 2009, gives great graphs of several types, some with an over-abundance of information that students will have to sort, select, and make sense of for themselves and their classmates. Statistics and percentages are topics that take on real meaning here.

If the class becomes interested in other diseases that have affected the world, they could research such epidemics as yellow fever. To get them into the story, look into Yellow Fever and the Reed Commission. They could research the number of victims over time and create a timeline from when the disease first reached the present United States up to the discovery of how to control it. A google search on “number of victims from yellow fever” brings up a few good sources, such as an August 10, 1879, article from The New York Times and another from September 24, 1897. Fascinating! But students will need to find other resources as well—encyclopedias and other books, offline as well as online. 

If the information found is sufficient, they could calculate rates of change over the course of different decades. Were there times when the disease rates rose more quickly? When they did not change at all? You could explore with them the concept of the slope of a line, what it actually tells us. Your students will find that numbers tell interesting stories! 


We Want Your Feedback
We want and need your ideas, suggestions, and observations. What
would you like to know more about? What questions have your
students asked? We invite you to share with us and other readers
by posting your comments. Please check back often for our newest
posts or download the RSS feed for this blog. Let us know what
you think and tell us how we can serve you better. We appreciate
your feedback on all of our Middle School Portal 2
publications. You can also email us at msp@msteacher.org. Post
updated 12/07/2011.

What’s the Difference Between Viruses and Bacteria?

Many people think that germs are what make us sick but scientifically speaking, germs are microbes that can be both harmful or helpful and come in four varieties – bacteria, viruses, fungi, and protozoa. We’ll leave the discussion of fungi and protozoa for another post and focus on bacteria and viruses in this one. Microbeworld says that viruses are as different from bacteria as goldfish are from giraffes. That is REALLY different! So what are the differences between the two microorganisms? With people still concerned with the H1N1 virus – knowing the differences and similarities might be really helpful!

What’s a Germ?
This page from Science NetLinks provides images of the four types of microbes and a general description of the differences between them.

Virus or Bacterium?
This site gets into more detail in regards to cell structure and reproductive differences.

What’s the Life Span of a Virus?
This podcast and background information tells the differences between the cold virus and flu virus – both life span and how they are transmitted.

Bacteria: More Than Pathogens
This article, written by molecular biologist Trudy Wassenaar, helps clear up the misconceptions associated with bacteria.

Structure Of ‘Beneficial’ Virus That Can Infect Cancer Cells Solved
There are lots of bacteria that are beneficial – not so much for viruses. Here is a Science Daily article that describes a virus that “attacks” cancer cells.


We Want Your Feedback
We want and need your ideas, suggestions, and observations. What would you like to know more about? What questions have your students asked? We invite you to share with us and other readers by posting your comments. Please check back often for our newest posts or download the RSS feed for this blog. Let us know what you think and tell us how we can serve you better. We appreciate your feedback on all of our Middle School Portal 2 publications. You can also email us at msp@msteacher.org. Post updated 11/21/2011.