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)!
