Environmental Engineering Reference
In-Depth Information
Several questions remain concerning the impact of insecticide resistance on the ef-
fi cacy of vector control operations. In Martinique (French West Indies), high levels of
resistance to the organophosphate temephos and the pyrethroid deltamethrin were re-
ported. This resistance was characterized by an important reduction of both mosquito
knock-down and mortality levels after thermal-fogging with deltamethrin and P450-
inhibitor synergized pyrethroids, indicating that resistance was negatively impacting
on control programs and that this resistance was conferred, at least in part, by elevated
cytochrome P450 activity [30].
In this study, we explored the mechanisms conferring insecticide resistance in an
Ae. aegypti
population from Martinique island. Larval bioassays and adult topical ap-
plications were used to determine the current resistance level of this population to in-
secticides. The presence of metabolic-based resistance mechanisms was investigated
by exposing mosquitoes to enzyme inhibitors prior to bioassays with insecticides and
by measuring representative enzyme activities of each detoxifi cation enzyme family.
At the molecular level, the frequency of the target-site
kdr
mutation was investigated
and a microarray approach followed by quantitative real-time RT-PCR validation was
used to identify detoxifi cation genes putatively involved in metabolic resistance. Re-
sults from this study will help to implement more effective resistance management
strategies in this major disease vector in the future.
Larval bioassays (Table 1) showed that the Vauclin strain is far less affected by
temephos than the susceptible Bora-Bora strain (RR
50
of 44-fold and RR
95
of 175-
fold). In the susceptible strain, temephos toxicity was not signifi cantly increased in the
presence of detoxifi cation enzyme inhibitors (PBO, DEF, and DMC). By contrast, the
level of resistance to temephos of the Vauclin strain was signifi cantly reduced in the
presence of PBO, DEF, and DMC (from 175 to 60, 44 and 109-fold respectively for
RR
95
) indicating the involvement of P450s, CCEs and in a lesser extent GSTs in the
resistance of larvae to temephos.
Table 1.
Insecticidal activity of temephos with and without enzyme inhibitors on larvae of
Aedes
aegypti
Vauclin and Bora-Bora strains.
Strain
Enzyme
inhibitor
Slope
(± SE)
LC
50
(j.tg/L)
(95% Cl)
LC
95
(j.tg/L)
(95% Cl)
RR
5o
(95% Cl)
RR
95
(95% Cl)
SR
5o
(95%
Cl)
SR
95
(95%
Cl)
8.49
(0.45)
3.7
(3.6-3.8)
5.7
(5.5-6)
−
−
−
−
−
8.28
(0.67)
4.2
(4-4.4)
6.7
(6.4-7)
0.87
(0.74-1 .03)
0.87
(0.74-1 .03)
PBO
−
−
Bora-Bora
8.13
(0.44)
3.3
(3.2-3.4)
5.3
(5. 1-5.6)
1.10
(0.98-1 .24)
1.10
(0.98-1 .24)
DEF
−
−
11.16
(0.54)
4.3
(4.2-4.4)
6.0
(5.8-6.2)
0.86
(0.79-0.94)
0.96
(0.81-1.14)
DMC
−
−
160
(150-
180)
2.08
(0.08)
1000
(870-1180)
44
(40-48)
175
(150-205)
−
−
−
140
(130-
150)
3.60
(0.24)
400
(360-450)
33
(29-38)
60
(51-71)
1.16
( 1.05-1.29)
2.52
(2.16-2. 95)
Vauclin
PBO
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