HOUSEHOLD AND STRUCTURAL INSECTS
Behavioral Activity of Catnip (Lamiaceae) Essential Oil Components
to the German Cockroach (Blattodea: Blattellidae)
CHRIS J. PETERSON, LEAH T. NEMETZ,
LEAH M. JONES,
AND JOEL R. COATS
Pesticide Toxicology Laboratory, Department of Entomology, Iowa State University, Ames, IA 50011
J. Econ. Entomol. 95(2): 377Ð380 (2002)
ABSTRACT The essential oil of catnip, Nepeta cataria L., contains two isomers of nepetalactone, E,Z-
and Z,E-nepetalactone, and was tested for repellent activity to adult male German cockroaches,
Blattella germanica (L.), in a choice-test arena. The two isomers of nepetalactone were puriÞed by
using preparative thin-layer chromatography and tested for behavioral activity in the choice-test
arena. SigniÞcant differences due to concentration were detected by analysis of variance, and the
responses were compared by least-squared means analysis. The activities of the essential oil and
puriÞed isomers were compared with N,N-diethyl-3-methylbenzamide (DEET) by a paired t-test.
E,Z-Nepetalactone was the most active of the compounds tested, being signiÞcantly more active to
this species than equivalent doses of DEET, the essential oil, or Z,E-nepetalactone. Antennectomized
insects showed no response to concentrations that were active against intact insects.
KEY WORDS Blattella germanica, catnip, nepetalactone, repellency
CATNIP,Nepeta cataria L., is well known for its intox-
icating effects on cats. The essential oil of catnip con-
tains the monoterpene-derived iridodial compound
clopenta[e]pyran-1-(4aH)-one) (McElvain et al.
1941), which exists in the plant as two isomers, Z,E-
and E,Z-nepetalactone (Fig. 1). The E,Z-isomer is the
more attractive of the two isomers to cats (Bates and
Sigel 1963). Catnip has folk uses as an insect repellent
and some uses have been conÞrmed scientiÞcally.
Nepetalactone vapors were shown to be repellent to
insect species in 13 families (Eisner 1964). Nepeta-
lactone is an important component of the defensive
secretions of the coconut stick insect, Graffea crouani
Le Guillou (Smith et al. 1979), and the lubber grass-
hopper, Romalea guttata (Houttuyn) (Snook et al.
1993). Other essential oils and individual monoterpe-
noids repel German cockroaches, Blattella germanica
(L.) (Inazuka 1982, 1983; Karr and Coats 1988; Coats
et al. 1991), as do various plant extracts (Schefßer and
Dombrowski 1992) and plant products (Appel and
In the current study, we describe the isolation and
puriÞcation of the two isomers of nepetalactone and
their behavioral effects against the German cock-
roach. Ethanol and ethyl ether extracts of catnip were
previously reported as being repellent to this species,
but there was no mention of the activity of the isomers
(Bodenstein and Fales 1976). We compared the activity
of the catnip essential oil and the two individual isomers
against N,N-diethyl-3-methylbenzamide (DEET, for-
merly N,N-diethyl-m-toluamide). First synthesized in
the early 1950s (McCabe et al. 1954), worldwide use
of DEET exceeded 200,000,000 persons in 1980 (EPA
1980). DEET can occasionally have severe adverse
effects on mammals (Miller 1982, Roland et al. 1985,
Snyder et al. 1986, Qiu et al. 1998). We tested the effect
of antennectomy on the behavioral response of B.
germanica to doses of extracts and compounds active
to intact B. germanica.
Materials and Methods
Plant Collection and Steam Distillation. The aerial
portions of N. cataria plants were collected from un-
sprayed areas of the Iowa State University campus,
Ames, IA, as needed during the growing season. Plants
not distilled immediately were frozen at Ð80⬚C. Plant
leaves and stems were cut by using scissors, placed into
a 5-liter, three-necked boiling ßask, and steam distilled
according to the method of Pavia et al. (1988). The
collected distillate was washed three times with one
volume each of hexane. The hexane was removed by
using rotary evaporation at 500 mm Hg vacuum at
Extract Analysis. A portion of the liquid obtained
from rotary evaporation was diluted to 1
hexane and subjected to chromatographic analysis.
Gas chromatographic analyses were conducted on a
Varian 3700 gas chromatograph (Palo Alto, CA) with
a 2-m packed OV-101 column, a nitrogen carrier, an
University of WisconsinÐStephens Point, Stephens Point, WI
Millikin University, Decatur, IL 62522.
To whom correspondence should be addressed.
0022-0493/02/0377Ð0380$02.00/0 䉷2002 Entomological Society of America
FID detector, an injection temperature of 250⬚C, an
injection volume of 1.5
l, and with an initial column
temperature of 70⬚C ramped at 5⬚C/min to 150⬚Cand
held for 8 min. High-performance liquid chromatog-
raphy (HPLC) was conducted by using a HewlettÐ
Packard 1100 HPLC (Palo Atlo, CA) with a Pirkle
Covalent Phenylglycine hi-chrom preparative column
(25 cm by 10 mm i.d., 5
m S5NH ModiÞed
Shereosorb, Regis Technologies, Morton Grove, IL),
with a mobile phase of 9:1 hexane/ethyl acetate at 2.5
ml/min ßow rate, and detection by using a Spectro-
ßow 757 UV-detector (Chestnut Ridge, NY) at 254 nm.
Separation of Nepetalactone Isomers. The two iso-
mers of nepetalactone were separated by using silica
gel preparative thin-layer chromatography plates (20
by 20 cm, 1,000
m in thickness, Whatman, Hillsboro,
OR) with a solvent system of 19:1 hexane/ethyl ether.
The plates were run seven times and allowed to dry
completely between runs. The products were visual-
ized under 254-nm UV light, and the silica gel was
scraped off the plates and washed with three washings
of ethyl ether. The ether was removed by rotary evap-
oration, and the purity of the isomers was assessed by
Instrumental Analysis of Isomers. Gas chromatog-
raphy/mass spectroscopy of the nepetalactone iso-
mers was conducted on a Varian 3400 gas chromato-
graph, with a DB-5 ms nonpolar 30-m capillary column
(0.25 mm i.d., J. & W. ScientiÞc, Folsom, CA). The
injector temperature was 250⬚C and the column tem-
perature was held at 150⬚C (isothermal). The gas chro-
matograph was coupled to a Finnigan TSQ 700 triple
quadrupolemass spectrometer (San Jose, CA), with an
electron impact of 70 eV.
Cockroach Bioassay. Adult male B. germanica were
obtained from a colony reared in our laboratory for
several years. Male German cockroaches have been
found by us (data not shown) and others (Schefßer
and Dombrowski 1992) to be more sensitive than
females to olfactory stimuli. The catnip essential oil
and the nepetalactone isomers were dissolved in hex-
ane, and DEET (Aldrich, Milwaukee, WI) was dis-
solved in acetone. A 12.5 cm round Þlter paper was cut
in half. One side was treated with 1 ml of the test
compound solution, and the other side was treated
with either acetone or hexane, depending upon which
solvent was used to dissolve the test material. The
papers were allowed to dry for ⬇2 min before being
placed in a 15 cm petri dish arena. The position of the
treated side (to the right or to the left) was random-
ized by using a random number table. The top of the
petri dish had a hole cut in the center for introduction
of the insect directly into the center of the arena. One
insect at a time was introduced. The hole was stopped
by using a small piece of tape to prevent escape of the
insect. Immediately after the introduction of the in-
sect, the number of seconds it spent on the treated or
untreated side in a total of 300 s (5 min) was timed with
two stopwatches. Filter papers and cockroaches were
used once then discarded. Repellency values were
calculated by subtracting the number of seconds the
insect spent on the treated side from the number of
seconds spent on the untreated side, dividing by the
total number of seconds (300), and then multiplying
that value by 100 to obtain a percentage. Each test was
replicated 10 times. All tests were run between 1000
and 1600 hours (CST) with overhead ßorescent light-
ing at ambient temperature (20Ð25⬚C) and humidity
For the tests that used antennectomized cock-
roaches, a razor blade was used to remove the anten-
nae at the scape. The cockroaches were allowed to
recover from the procedure for 24 h before being
exposed to the test compounds by the method out-
lined in the previous paragraph.
SigniÞcance due to concentration was determined
by using ANOVA, and means for each dose were
compared by least-squares means analysis (SAS Insti-
tute 1991) to determine doseÐresponse relationships.
Comparisons between compounds or treatments were
made by using a paired t-test.
Results and Discussion
By using gas chromatography, we determined that
the catnip essential oil contained Z,E-nepetalactone
and E,Z-nepetalactone in a 6:1 ratio, or roughly 85:
15%. Bates and Sigel (1963) reported a ratio of 3:1
Z,E-nepetalactone to E,Z-nepetalactone, or 75:25%.
These isomers together comprised 98% of the steam
distillate, and minor components were not identiÞed.
Mass spectral analysis revealed that the two isomers
are indistinguishable. Z,E-Nepetalactone eluted off
the DB-5 ms column at 2.45 min and showed ions at
m/z 166 [M
] (100%), m/z 123 (78.5%), m/z 109
(46.3%), m/z 95 (58.8%), m/z 81 (62.2%), and m/z 69
(46.7%). E,Z-Nepetalactone eluted off the column at
2.65 min and had the following mass spectrum: m/z 166
] (100%), m/z 123 (99.9%), m/z 109 (51.8%), m/z
95 (66.6%), m/z 81 (67.0%), and m/z 69 (50.2%).
SigniÞcance due to concentration was observed by
two-tailed ANOVA for DEET (F⫽4.83; df ⫽5, 54; P⫽
0.001), Z,E-nepetalactone (F⫽20.00; df ⫽4, 45; P⫽
0.0001), and E,Z-nepetalactone (F⫽41.08; df ⫽2, 27;
P⫽0.0001). SigniÞcance due to concentration was not
seen for the catnip essential oil at the 0.05 two-tailed
signiÞcance level, but was seen at the 0.1 signiÞcance
level (F⫽3.44; df ⫽3, 36; P⫽0.0267). Repellency
values (% ⫾SEM) were calculated and means were
compared by using least-squares means analysis (Ta-
ble 1). All DEET concentrations tested at ⬍1,600
were not signiÞcantly different from the control
by least-squared means analysis (
⫽0.05). The be-
Fig. 1. Nepetalactone isomers from catnip.
378 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 95, no. 2
havioral response to catnip essential oil was signiÞ-
cantly different from the control at a dose of 800
. The response to Z,E-nepetalactone was sig-
niÞcantly different from the control at doses of 160
and higher. The response to E,Z-nepetalac-
tone was signiÞcantly different from the control at all
doses tested (down to 16
Paired t-test comparisons (
⫽0.05, df ⫽9) be-
tween the different compounds at equivalent doses
were made. The response of the cockroaches to catnip
essential oil differed signiÞcantly from DEET at 800
, and did not differ from it at lower doses. The
response to Z,E-nepetalactone differed from equiva-
lent doses of DEET above 80
and the response
to E,Z-nepetalactone differed signiÞcantly from
DEET at all concentrations tested, down to 16
The response to Z,E-nepetalactone, which comprised
⬇85% of the essential oil, did not differ signiÞcantly
from the response to catnip essential oil at any of the
concentrations tested. E,Z-Nepetalactone was more
active than the catnip essential oil at 80
Z,E-andE,Z-nepetalactone were compared at 80 and
,andE,Z-nepetalactone was signiÞcantly
more active than the Z,E- isomer at both concentra-
tions. Catnip essential oil should be more active than
the Z,E-isomer alone because the oil contains ⬇15% of
the more active E,Z-isomer. This was not observed,
perhaps because the variability inherent in behavioral
tests obscures statistical determination of differences.
Visual examination of the results indicates that the
essential oil may be more active than the Z,E-isomer
at the two lowest doses (80 and 16
), and more
rigorous testing may statistically reveal the expected
Antennectomy of adult male cockroaches resulted
in a diminished response to the test compounds
⫽0.05, df ⫽9) (Table 2). In the three
comparisons, the amount of time the antennecto-
mized insects spent on either the treated or untreated
side did not differ signiÞcantly by the paired t-test.
This indicates that the chemoreceptors involved in
this behavioral response are probably located on the
The results presented herein indicate that catnip
essential oil and the isomers of nepetalactone cause
German cockroaches to spend less time in treated
areas. These compounds may be useful in the devel-
opment of exclusion barriers to prevent entry of in-
sects into sensitive areas; e.g., kitchens, childrenÕs
nurseries, and hospital rooms. Using such compounds
in shipping containers may reduce the incidence of
accidental pest introduction to novel areas. That these
compounds are volatile and the response was olfactory
(rather than contact) may be important in providing
protection over a large area, because the insects will
not have contact with the treated surfaces. Volatility,
however, may shorten the effective time. This prob-
lem may be alleviated by special formulations, such as
microincapsulation, to reduce volatile loss. Using
these compounds as part of a “push-pull”system, re-
pelling the insects out of one area and luring into an
attract-and-kill system in another, also may be possi-
We thank Erin Schneider and Lindsay Searle for help in
the laboratory. We thank the Program for Women in Science
and Engineering at Iowa State University, Ames, IA, and Iowa
State University Instrument Services, Department of Chem-
istry, Iowa State University, Ames, IA. This is journal paper
J-19112 of the Iowa Agriculture and Home Economics Ex-
Table 1. Percentage repellency (ⴞSEM) of DEET and catnip
compounds to male B. germanica in a choice-test assay
Test solution Dose (
DEET 1,600 58.3 ⫾10.5b
800 25.8 ⫾9.5a
160 20.4 ⫾9.2a
80 15.5 ⫾5.4a
16 15.4 ⫾5.9a
0 5.2 ⫾7.5a
Catnip essential oil
800 55.6 ⫾9.8b
160 27.7 ⫾13.1ab
80 33.7 ⫾15.7ab
16 31.7 ⫾8.1ab
0 2.9 ⫾3.7a
800 68.2 ⫾5.7b
160 56.8 ⫾7.8b
80 15.4 ⫾6.9a
16 16.1 ⫾7.4a
0 2.9 ⫾3.7a
80 79.4 ⫾3.5c
16 46.4 ⫾11.0b
0 2.9 ⫾3.7a
For each test solution, repellency values followed by the same letter
are not signiÞcantly different by least-squares means analysis (
0.05). Repellency ⫽[(no. of seconds spent on untreated side ⫺no.
of seconds spent on treated side)/300] ⫻100.
Table 2. Results of behavioral assay of antennectomized male German cockroaches, and paired ttest comparison with nonanten-
nectomized male cockroaches tested at the same concentration
Antennectomized Nonantennectomized Calculated tvalue
1600 DEET 1.7 ⫾11.4 58.3 ⫾10.5 3.03*
160 Z,E-Nepetalactone 19.8 ⫾7.0 56.8 ⫾7.8 3.40*
80 E,Z-Nepetalactone ⫺1.3 ⫾10.2 79.4 ⫾3.5 7.84*
% Repellency ⫽[(no. of seconds spent on untreated side ⫺no. of seconds spent on treated side)/300] ⫻100.
*, Difference is signiÞcant by two-tailed paired ttest at
⫽0.05, df ⫽9.
April 2002 PETERSON ET AL.: ACTIVITY OF CATNIP COMPONENTS TO B. germanica 379
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Received for publication 19 March 2001; accepted 22 August
380 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 95, no. 2