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JOURNAL OF MOSQUITO RESEARCH
12
concentrations ranging from 12.5~150 ppm for
P.
glandulosus
and from 50~250 ppm for
C. rigidus
against larvae; from 25~300 ppm for both plants
against pupae except
C. rigidus
against
Cx.
quinquefasciatus
(100~500 ppm) were used. For
comparison, a commercial formulation of WARRIOR
®
1000 EC (100 % DDVP: 2,2-dichlorovinyl dimethyl
phosphate) larvicide and pupicide (2000 ppm,
recommended concentration) bought from Awka
market (Anambra State, Nigeria) was used as positive
control. 1 ml of Tween 80 in 99 ml of tap water was
used as negative control. These controls were set up
for each replicate, mosquito species and plant. All the
concentrations were chosen after a preliminary test for
each essential oil and mosquito species. Twenty-five
4
th
instar mosquito larvae or early pupae were released
into each 250 ml beaker containing 100 ml of the
aliquot and mortality was recorded after 24 h of
exposure. No food was provided either to the tests or
controls during the experiments. The dead larvae and
pupae were expressed as percentage mortality at each
concentration. In cases where bioassay tests showed
more than 20% (negative) control mortality, these
were discarded and repeated. However when negative
control mortality ranged from 5-20%, the observed
percentage mortality was corrected by Abbott's
formula. The larvae or pupae were considered as dead,
if they were not responsive to a gentle prodding with a
fine needle. All bioassays were carried out at room
temperature of (27±2)
℃
and (79±2)% RH. Experiments
were set in four replicates along with controls.
% Mortality = (number of larvae or pupae dead / total
number of larvae or pupae used) * 100.
Corrected Mortality (%) = [(% test mortality - %
control mortality) / (100
-
control mortality)] x 100
(Abbott, 1925).
3.5 Statistical analysis
The corrected mortality was determined using
Abbott’s (1925) formula whenever required. The
percentage of mortality data were subjected to
ANOVA procedure using Statistical Package for
Social Science (SPSS 17.0). Duncan test (P=0.05) was
applied for mean separation. Probit analysis (Finney,
1971) was applied to determine lethal dosages causing
50 % (LC
50
) and 90 % (LC
90
) mortality of larvae and
pupae 24 h post exposure.
Aknowledgements
Authors gratefully acknowledge the equipment facilities
provided by the Faculty of Pharmaceutical Sciences, Agulu;
Nnamdi Azikiwe University, Awka; Anambra State, Nigeria.
Grateful thanks are due to the staff members of the same
institution for their cooperation. We are also thankful to
WHO/National Arbovirus and Vector Research Centre Enugu,
Enugu state, Nigeria for the provision of mosquito species used
in this project.
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