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Linked from this Travel.SE answer, I saw a surprising claim in Science Daily from 2001:

Researchers report that nepetalactone, the essential oil in catnip that gives the plant its characteristic odor, is about ten times more effective at repelling mosquitoes than DEET — the compound used in most commercial insect repellents.

The article doesn't link to any paper, saying instead that it was "reported today at the 222nd national meeting of the American Chemical Society", by "the same Iowa State University research group that two years ago discovered that catnip also repels cockroaches" (related, unanswered Skeptics question), led by "Entomologist Chris Peterson, Ph.D., with Joel Coats, Ph.D., chair of the university’s entomology department".

Apparently the test was done using Aedes Aegypti mosquitoes (which spread Yellow Fever, Dengue Fever and Zika virus). The article adds:

Peterson says catnip should work against all types of mosquitoes

DEET is the most commonly used mosquito repellent, recommended by CDC and others, but has side effects including skin irritation and melting some plastics and synthetic materials.

If there was a more powerful alternative to DEET, that would seem pretty significant - but I've never seen any catnip-based insect repellent for sale or recommended for use, despite 15 years having passed since this study. This makes me skeptical.

I've found one snakeoil-looking site selling catnip based repellent, which repeats the claim and includes what it presents as their own copy of the report's press release (hosted on the shop's own domain, so possibly not genuine) plus a dead link claimed to be to the original report.

Is there good evidence that catnip, or specifically nepetalactone, work as claimed, and can be used by humans as an effective repellent to all kinds of biting mosquitoes?

  • Criticism on the entomological accuracy of the 2001 findings is present here-salinella.bio.uottawa.ca/BIO3323/Outline/assignment2004/… and further studies on safety is required when one reviews the summary here- miskeptics.org/2011/06/… – pericles316 Feb 4 '16 at 12:41
  • @pericles316: Second link seems broken. is this an answer? – Oddthinking Feb 4 '16 at 12:44
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    @Oddthinking-Thought it would help someone in forming one and try this link-miskeptics.org/2011/06/…! – pericles316 Feb 4 '16 at 12:50
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    Note that catnip (the plant) is not the same thing as an oil extracted from it. Nepetalactone may be very effective, but if the plant doesn't have much of the oil in its leaves then the effectiveness of rubbing catnip leaves on you will be less. – Paul Johnson Feb 6 '16 at 17:41
  • Maybe it would work in Europe, but I've got my doubts about the sanity of spraying yourself with catnip before heading out into cougar country. – Mark Feb 9 '16 at 1:32
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+100

First, it is important to understand the terminology being used.

There is the plant catnip.

From the plant catnip, catnip essential oil can be obtained by steam distillation. Only a tiny fraction of the plant material is essential oil.
According to Catnip as a Source of Essential Oils

Oil yield ranged from 0.1 to 0.2 mL/100 g dry wt

One class of compounds in catnip essential oil is nepetalactones.

According to the above reference, in catnip essential oil

nepetalactones ranged from 6.0% to 73.2% of the total EO [essential oil]

And the nepetalactones occur as E,Z and Z,E isomers, which differ in repellency activity.

The 2001 Science Daily article mentioned in the OP says "[Chris] Peterson says nepetalactone is about 10 times more effective than DEET because it takes about one-tenth as much nepetalactone as DEET to have the same effect."

In 2006 the same Chris Peterson and coauthors wrote Natural Insect Repellents: Activity against Mosquitoes and Cockroaches which gives quantitative results for catnip essential oil and DEET. In some individual tests, when initially applied, catnip essential oil nominally showed greater repellency, but it is not stated to be statistically significant (see "Treatments with the same letter are not significantly different by Tukey analysis at [alpha] = 0.05." in each of Figs. 3-5). Furthermore, catnip essential oil was shown to have statistically significant decline in effectiveness over a 3 hour period, while DEET showed no decline.

Mosquito Repellency

Percentage repellency of catnip and Osage orange essential oil, elemol and DEET at 15 minutes is represented in Figures 3,4, and 5. All compounds tested showed various levels of significance in percentage repellency and contact repellency. The overall concentration effect was not significant (P = 0.4569). Osage orange essential oil represented the lowest values in percentage repellency (<60%) and did not show any significant contact repellency (P = 0.1). Catnip essential oil showed high percentage repellency at the 15-minute time-point at all concentrations tested, including the highest value, 100% from the 0.1% concentration (Figure 5). This was also the most significant level of contact repellency (P <0.0001) resulting from the three concentrations of catnip essential oil (Table III). The other concentrations of catnip essential oil varied in contact repellency (0.5% concentration, P = 0.5, and 1% concentration, P = 0.02). Elernol solutions yielded the second highest set of percentage repellency values of the test solutions, ranging from 81 % to 63%. These treatments also resulted in highly significant contact repellency (Table III). The commercially available standard for mosquito repellency, DEET, also showed high percentage repellency values, ranging from 63% to 44%, in addition to high significance for contact repellency.

Residual Repellency

Percentage repellency values were high for catnip essential oil, elemol, and DEET solutions immediately following application to the test surface (Table IV). The analysis of variance showed that there was a difference among the three different solutions and the control (P < 0.0001), and a significant interaction with treatment solution and time (P = 0.0019). The only treatment solutions to show a significant decrease in percentage repellency over time were 0.5% catnip essential oil (P = 0.02) and 0.1% catnip essential oil (P = 0.003) in which 51% of the variability in the data was explained by this negative linear relationship. Elemol, DEET, and control treatments did not show significant trends in the regression analysis, indicating maintenance of repellency with elemol and DEET over the 3-hour period.

Conclusion

Mosquitoes exposed to DEET and elemol settled far enough from the treated surface to achieve an adequate level of contact repellency. As time increased, individuals would continually reject the treated surface up to the end of the 180-minute period, unlike the carnip essential oil, which exhibited an initially high repellency response that decreased over time. DEET and elemol showed a longer duration of repellency compared to catnip essential oil, as is evidenced with higher significance in contact repellency. Additional studies are needed to better understand how these differences occur, including studies on the chemical volatilization, and interference with behavioral stages of mosquito host-finding and acceptance.

The second mosquito assay focused on quantifying the residual repellency of the northern house mosquito to aged filter papers of catnip essential oil, elemol and DEET. All 0.5% and 0.1% test solutions showed significant percentage repellency following application (i.e., with no ageing period). This repellency effect slowly decreased over time for both concentrations of catnip essential oil (0.5%, P=0.02, 0.1%, P=0.003). There was no significant loss in percentage repellency seen in the DEET and elemol treatment solutions, accounting for continual mosquito repellency over 3 hours from a treated surface. Olfactory repellency differs from contact repellency, and the method used here allows for some differentiation between the two types. The high initial repellency of catnip essential oil is not sustained over a 3-hour period, but elemol and DEET do show residual repellency to that time-point.

Essential Oils in Insect Control: Low-Risk Products in a High-Stakes World adds

catnip oils are attractive to some species of felines, ... this product is definitely not recommended in cougar or puma (Felis concolor) country (e.g., the Rocky Mountains)!

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