Centre Suisse de Recherche Scientifique en Cote d'Ivoire (CSRS), Abidjan, 01BP1303, Côte d'Ivoire.
BMC Infect Dis. 2012 Sep 13;12:214. doi: 10.1186/1471-2334-12-214.
Appropriate monitoring of vector insecticide susceptibility is required to provide the rationale for optimal insecticide selection in vector control programs.
In order to assess the influence of mosquito age on susceptibility to various insecticides, field-collected larvae of An. gambiae s.l. from Tiassalé were reared to adults. Females aged 1, 2, 3, 5 and 10 days were exposed to 5 insecticides (deltamethrin, permethrin, DDT, malathion and propoxur) using WHO susceptibility test kits. Outcome measures included the LT50 (exposure time required to achieve 50% knockdown), the RR (resistance ratio, i.e. a calculation of how much more resistant the wild population is compared with a standard susceptible strain) and the mortality rate following 1 hour exposure, for each insecticide and each mosquito age group.
There was a positive correlation between the rate of knockdown and mortality for all the age groups and for all insecticides tested. For deltamethrin, the RR50 was highest for 2 day old and lowest for 10 day old individuals. Overall, mortality was lowest for 2 and 3 day old individuals and significantly higher for 10 day old individuals (P < 0.05). With permethrin, the RR50 was highest for 1 to 3 day old individuals and lowest for 10 day old individuals and mortality was lowest for 1 to 3 day old individuals, intermediate for 5 day old and highest for 10 day old individuals. DDT did not display any knockdown effect and mortality was low for all mosquito age groups (<7%). With malathion, the RR50 was low (1.54 - 2.77) and mortality was high (>93%) for all age groups. With propoxur, no knockdown effect was observed for 1, 2 and 3 day old individuals and a very low level of mortality was observed (< 4%), which was significantly higher for 5 and 10 day old individuals (30%, P < 0.01).
Results indicate that for An. gambiae s.l. adults derived from wild-collected larvae, there was an influence of age on insecticide susceptibility status, with younger individuals (1 to 3 days old) more resistant than older mosquitoes. This indicates that the use of 1 - 2 day old mosquitoes in susceptibility assays as recommended by the WHO should facilitate detection of resistance at the stage where the highest rate of the resistance phenotype is present.
为了提供在蚊虫控制项目中选择最佳杀虫剂的依据，需要对病媒昆虫杀虫剂敏感性进行适当监测。
为了评估蚊虫年龄对各种杀虫剂敏感性的影响，从蒂阿萨莱采集的冈比亚按蚊幼虫被饲养至成虫。将 1、2、3、5 和 10 天龄的雌性蚊子暴露于 5 种杀虫剂（溴氰菊酯、氯菊酯、滴滴涕、马拉硫磷和残杀威），使用世界卫生组织（WHO）敏感性测试试剂盒进行测试。测量指标包括半数击倒时间（LT50，实现 50%击倒所需的暴露时间）、抗性比（RR，即野生种群比标准敏感株系的抗性高出多少）以及每种杀虫剂和每个蚊子龄组暴露 1 小时后的死亡率。
对于所有年龄组和所有测试的杀虫剂，击倒率和死亡率之间存在正相关关系。对于溴氰菊酯，2 天龄和 10 天龄个体的 RR50 最高。总体而言，2 天龄和 3 天龄个体的死亡率最低，而 10 天龄个体的死亡率显著更高（P<0.05）。对于氯菊酯，1 至 3 天龄个体的 RR50 最高，10 天龄个体的 RR50 最低，1 至 3 天龄个体的死亡率最低，5 天龄个体的死亡率居中，10 天龄个体的死亡率最高。滴滴涕没有表现出任何击倒效果，所有蚊子龄组的死亡率都很低（<7%）。对于马拉硫磷，RR50 较低（1.54-2.77），所有年龄组的死亡率都很高（>93%）。对于残杀威，1、2 和 3 天龄个体没有表现出击倒效果，死亡率非常低（<4%），而 5 天龄和 10 天龄个体的死亡率则显著更高（30%，P<0.01）。
结果表明，对于源自野生幼虫的冈比亚按蚊成虫，年龄对杀虫剂敏感性状态有影响，年轻个体（1 至 3 天龄）比年长的蚊子更具抗性。这表明，按照世界卫生组织的建议，在敏感性测定中使用 1-2 天龄的蚊子，应有助于在最高抗性表型率出现的阶段检测到抗性。
