Increase in susceptibility to insecticides with aging of wild Anopheles gambiaemosquitoes from Côte d’Ivoire

Abstract

BackgroundAppropriate monitoring of vector insecticide susceptibility is required to provide the rationale for optimal insecticide selection in vector control programs.MethodsIn 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.ResultsThere 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).ConclusionResults 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.

Effects of Age and Larval Nutrition on Phenotypic Expression of Insecticide-Resistance in Anopheles Mosquitoes

“…However, its effect was small and was apparent only in one of our two colonies and if the mosquitoes were exposed fairly early after emergence. Furthermore, corroborating other studies [3]–[5], in both colonies post-exposure survival decreased with the age at exposure to DDT.…”

“…First, sensitivity to insecticides increases as mosquitoes age [3]–[5]. This may be at least partly explained by an age-related decline in the expression of insecticide detoxification genes [4] (but see [3], [6] ).…”

Combined target site (kdr) mutations play a primary role in highly pyrethroid resistant phenotypes of Aedes aegypti from Saudi Arabia

“…In common with previous studies on Ae. aegypti and other mosquitoes [37, 38] ten-day-old females from Makkah and Jeddah were significantly more susceptible to deltamethrin than 3–5 days olds, though with a standard 60 min exposure the majority still survived. With long exposure times of six or eight hours up to 30% survival was observed, demonstrating that not only are most of the population classed as resistant (from 60 min bioassay data), but a small proportion is highly resistant, even when tested as older females.…”

Quantification of permethrin resistance andkdralleles in Florida strains ofAedes aegypti(L.) andAedes albopictus(Skuse)

“…When the RR is between 5 and10, the mosquitoes are considered to have moderate resistance. A RR greater than 10 indicates that mosquitoes are highly resistant [27].…”