Journal of the American Mosquito Control Association, 10(4)14'73-476,
Copyright @ 1994
by the American Mosquito Control Association,
FAILURE OF THE "MOSQUITO PLANT",
PELARGONIUM X CITROSUM'VAN LEENII"
TO REPEL ADULT AEDES ALBOPICTU^S AND
CULEX QUTNQUEFASCIATUS IN FLORIDA
J. E. CILEK exp E. T. SCHREIBER
ABSTRACT. The efrcacy of the "mosquito plant", Pelargonium x citrosum
'van Leenii', as an area-
wide repellent against adult host-seeking I edes albopictus and Culex quinquefasciatus
females was eval-
uated. No significant differences
(P > 0.05) were observed in the number of mosquitoes landing on the
of human subjects in locations where
plants were present
In laboratory cage trials, more Cx. quinErcfasciatus adults rested on excised leaves of this cultivar
compared side-by-side with similar size and shape white paper
A variety of botanical substances have been
for their repellency
against adult mos-
1947, Dethier 1947,
umar et al. 1991). In many
oils" that were extracts from
whole or parts of plants.
One of the earliest well-
known mosquito repellents (being used as early
is the essential oil ofcitronella
1947). This substance is currently available in
commercially formulated repellents.
inally extracted from the citronella or nardus
nardus Linn., and found to
be composed of a variety of acyclic monoter-
including borneol, geraniol, citronellol, and
citronellal (Christophers 1947, Dethier 1947\.
Some of these compounds are common repel-
lents found in the alarm substance
and kvin 1976).
We have seen a variety of garden
businesses from the USA and Canada advertis-
ing a "mosquito plant" also sometimes
to as "citrosa plant" or "citrosa
common names refet to Pel-
argonium x citrosum'van Leenii' Voigt ex T.
a plant that pro-
duces citronella oil and that is claimed to "be
the only effective
plant in the
world". This plant is a cross of an African lemon
geranium (P. x limoneum) hybid that further
citronella oil. This resultant
been attributed to the efforts of Dutch
horticulturist, Dirk Van Leenen. Mosquito re-
pellency of the 'van Leenii' cultivar is implied
by vaporization ofplant volatiles (i.e.,
oil) into the surrounding environment and is
to provide a barrier ofprotection against
within a 3-m-diam area.
Our study was initiated to evaluate,
in field and
laboratory trials, the repellency
ofP. x citrosum
'van Leenii', in north Florida against adult host-
of Aedes albopictus
Say, 2 common urban
MATERIALS AND METHODS
in a 13.9 x 7.2 x
enclosure at the John A. Mul-
rennan, Sr. Research
FL. At l4-d intervals, l0 P. x citrosum'van
0.5 m apart in
one end of the enclosure in a 1.6-m-diam circle
30 min before each study began to allow plant
volatiles to equilibrate in the immediate area
trials l-5. At weeks 14 through 18 (trials 6-8),
in the test location for 24 h prior
to mosquito release
and collections. An area
9 m from the
at the other end of the enclosure), was
a control. Fifteen minutes later (af-
ter plants had been set out), approximately 500
Ae. albopictus and 1,000 Cx. quinquefasciatus
laboratory-reared 5-6-day-old nonbloodfed fe-
in the middle ofthe screened
before collections commenced. After
the 30-min equilibration time 2 people sat in
ends ofthe enclosure in
the middle of each
test area and mosquitoes
on theirbare forearms were
an aspirator (Hausherr's
Machine Works, Toms
River, NJ). Four 5-min collection periods ex-
individual twice at each
plant vs. control). After these collections,
were switched to the control area and the pre-
vious "treatment" area then became a control.
Thirty minutes was allowed to elapse before
474 Joururar or rxp Ar"reruclN
MosQuro Covrnor, Assocr,r^nox No.4
Table 1. Total number of Aedes albopictus and Culex quinquefascialus
the forearms of 2 human volunteers in areas with and without Pelargonium x citrosum'van
kenii', moming tests.
Trial Cx. quinque-
Ae. albopictus fasciatus Ae. albopictus Cx. quinque-
I All r-values
P > 0.05.
the next set of mosquito collections.
allowed any volatiles in the previous treatment
area to dissipate
and volatiles in the new treat-
with plants to equilibrate.
collected were identified and
the number aspirated
corded at each time interval. Because of host-
between the 2 species,
study was conducted during early morning and
late evening crepuscular
periods. No wind was
felt by the investigators during testing.
from the study
area and placed in a 2nd screened
from the study site, similar to the first. The study
from August 5 through Novem-
ber 5, I 993. Heights ofeach plant were
on the day of testing.
21.3 ! I .0"C and for evening
26.9 + 0.8oC.
Our study used
sign similar to that used by Schreiber
et al. ( l99l)
utilizing the statistical analysis
of Cochran and
Cox (1957). This design recognized 2 main
ofvariation: l) bloodfeeding
host-seeking female mosquitoes fluctuates
through time, and 2) rate of attack varied from
human subject to human subject.
Briefly, 2 in-
dividuals (A, B) were subjected
and P (control [i.e., no plant] and plant, respec-
tively) at 2 locations (R, S). The 4 5-min test
periods exposed each individual to each treat-
ment in each
location using the following order
of rotation: C-R, P-R, C-S,
R-S for subject
P-S, C-S, P-R, C-R for subject
the total number ofmosquitoes
in control (no plant) vs. plant sites
a l-test. Differences
at P > 0.05.
t€sts of excised
P. x citrosum
'van lrenii' leaves
repellency to adult Cx. quinquefas-
On the day before
100 5-day old adult females
of 4 42 x 42 x 42-cm screened
opposite sides of clear Plexiglas@.
of4 plants and the severed
with paraffin wax. The upper sur-
face of each leaf was taped to a l5-cm-diam
Whatman #4 filter paper
disc and fastened
at the back ofeach cage.
filter paper model (designated
as a control), to mimic the'van Leenii'leaf, had
previously cut out ofthe same
to another l5-cm-diam filter paper
disc and immediately fastened to the back of the
leaves and paper models were ap-
proximately I 2 cm from each other on the screen
in the same
and were about 38 cm
from the cage
floor. In previous tests,
ence in the number of mosquitoes landing on
green vegetable-dyed filter paper leaves placed
on a l5-cm-diam filter paper
compared with similarly presented uncolored
(white) filter paper leaves.
a control. Total number of
resting on leaves and
every half hour (at 3 l-min
intervals) for 8 h. All plants for this study were
obtained locally from a commercial hardware/
RESULTS AND DISCUSSION
The total number of mosquitoes,
that landed on persons
in the screened
was not significantly
lower in locations
where P. x citrosum'van Leenii' was present
ztneoNtu*t x crrRosuM Anre-Wrpr Rerer-r,sNcy
Table 2. Total number of Aedes
albopictus and Culex quinquefascialas
females collected from
the forearms of 2 human volunteers in areas
with and without Pelargonium x citrosum'varr
Leenii', evening tests.
Trial Cx. quinque-
Ae. albopictus fasciatus Cx. quinque-
Ae. albopictus fasciatus /-valuet
'All t-values not sigrificant, P > 0.05.
compared with controls in morning (Table l) or
2). Literature accompanying
of this cultivar states
that one plant should be able to provide enough
volatile chemicals to repel mosquitoes
area. Our study used l0 times the number
ofplants in an area ofthis size with no significant
reduction in the number of host-seeking
quitoes. In addition, plant height (i.e., size)
not afect repellency
during the study. Plant height
at the beginning
of the tests
averaged 28.7 + 1.9
cm and at the end ofthe test averaged
3.2 cm. Individual area
cm,). During field
that several mosquitoes
on the plants and used
them for resting
laboratory cage tests
ber of female
on excised leaves
l) compared with paper leaf model controls
Although the'van Leenii' cultivar smelled like
it emitted citronella, no mosquito repellency
observed as a result of volatiles emitted from
these plants. Citronellal (one of the repellent
components in oil of citronella) has been re-
ported to be sufficiently volatile to keep mos-
at a distance
and Brown I 95 I ).
However, only the purified form of this com-
used for this observation
and not cit-
ronella-producing plants themselves.
oil ofcitronella (as
a complex of components
of which ge-
raniol and citronellal are the chiefactive agents
47, D ethier I 9
sidered as an olfactory deterrent (Garson and
contact or gustatory repellency
may exist. Citronellol, another
component of oil
also been reported to deter ovi-
position by the sweetpotato whitefly (Bemisia
tabaci (Gennadius)) via contact (Butler et al.
Evidently in our study the volatiles that are
produced from P. x citrosum 'van kenii'were
either not intrinsically repellent or not released
in sufficient quantity to evoke a repellent re-
to create a barrier against host-seeking
and Cx. quinquefascialzs
It is quite probable
that the leaves
may have to be crushed
or rubbed on the skin
the volatile components of citronella
We thank C. H. Hallmon for his assistance in
and help in field tests and J.
S. Coughlin and M. A. Olson for their help with
the laboratory tests, plant measurements,
Lastly, we thank K. D. Perkins,
University of Florida Herbarium, Gainesville,
for providing identification and additional in-
formation about P. x citrosum 'van Leenii'. We
appreciate W. Opp, J. P. Smith, and G. Alex-
ander for bringing this plant cultivar to our at-
tention. Acknowledgment is extended to those
that contributed critical reviews ofpre-
D. L. Coudriet
1989. Sweetpotato whitefly:
oils on cotton.
476 JounNlr or rrre Ar'cnrclN Moseurro Coxrnor, AssocllnoN Vor. 10. No. 4
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D. S. and A. W. A. Brown. 1951. Studies
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