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Efficacy of three insecticides against Anopheles dirus and Anopheles minimus, the major malaria vectors, in Kanchanaburi Province, Thailand.

The Southeast Asian journal of tropical medicine and public health (2013-02-19)
Dechen Pemo, Narumon Komalamisra, Sungsit Sungvornyothin, Siriluck Attrapadung
ABSTRACT

We conducted this study to determine the insecticide susceptibility of two malaria vectors, Anopheles dirus and Anopheles minimus from Kanchanaburi Province, Thailand. The mosquitoes were collected and reared under laboratory conditions. The test was carried out on unfed F-1 female mosquitoes using a standard WHO testing protocol. The LD50 and LD90 of deltamethrin in both species were tested for by exposing the mosquitoes to various doses of deltamethrin for 1 hour. The lethal time was also tested among mosquitoes by exposing them to deltamethrin (0.05%), permethrin (0.75%) and malathion (5%), for different exposure times, ranging from 0.5 to 15 minutes. Percent knockdown at 60 minutes and mortality at 24 hours were calculated. The resistance ratio (RR) was determined based on the LD50 and LT50 values. LD50 of deltamethrin against An. dirus and An. minimus were 0.00077% and 0.00066%, respectively. LT50 values for deltamethrin (0.05%), permethrin (0.75%) and malathion (5%) against An. dirus and An. minimus were 1.20, 3.16 and 10.07 minutes and 0.48, 1.92 and 5.94 minutes, respectively. The study revealed slightly increased tolerance by both mosquito species, compared with laboratory susceptible strains, based on LD50 values. The two anopheline species had the same patterns of response to the three insecticides, based on LT50 values, although the LT50 values were slightly higher in the An. dirus population. Both An. dirus and An. minimus were fully susceptible to all the insecticides tested, with 100% mortality at 24 hours post-exposure. Deltamethrin was the most effective insecticide, followed by permethrin and malathion.

MATERIALS
Product Number
Brand
Product Description

Supelco
Malathion, certified reference material, TraceCERT®
Supelco
Malathion solution, 100 μg/mL in cyclohexane, PESTANAL®, analytical standard
Supelco
Malathion, PESTANAL®, analytical standard
Supelco
cis-Permethrin solution, 10 μg/mL in cyclohexane, PESTANAL®, analytical standard
Supelco
trans-Permethrin solution, 10 μg/mL in cyclohexane, PESTANAL®, analytical standard
Supelco
Permethrin, PESTANAL®, analytical standard