Effect of environmental variables and kdr resistance genotype on survival probability and infection rates in Anopheles gambiae (s.s.)

Abstract

BackgroundEnvironmental factors, especially ambient temperature and relative humidity affect both mosquitoes and malaria parasites. The early part of sporogony is most sensitive and is affected by high temperatures and temperature fluctuation immediately following ingestion of an infectious blood meal. The aim of this study was to explore whether environmental variables such as temperature, together with the presence of the kdr insecticide resistance mutations, have an impact on survival probability and infection rates in wild Anopheles gambiae (s.s.) exposed and unexposed to a pyrethroid insecticide.MethodsAnopheles gambiae (s.s.) were collected as larvae, reared to adults, and fed on blood samples from 42 Plasmodium falciparum-infected local patients at a health facility in mid-western Uganda, then exposed either to nets treated with sub-lethal doses of deltamethrin or to untreated nets. After seven days, surviving mosquitoes were dissected and their midguts examined for oocysts. Prevalence (proportion infected) and intensity of infection (number of oocysts per infected mosquito) were recorded for each group. Mosquito mortality was recorded daily. Temperature and humidity were recorded every 30 minutes throughout the experiments.ResultsOur findings indicate that apart from the effect of deltamethrin exposure, mean daily temperature during the incubation period, temperature range during the first 24 hours and on day 4 post-infectious feed had a highly significant effect on the risk of infection. Deltamethrin exposure still significantly impaired survival of kdr homozygous mosquitoes, while mean daily temperature and relative humidity during the incubation period independently affected mosquito mortality. Significant differences in survival of resistant genotypes were detected, with the lowest survival recorded in mosquitoes with heterozygote L1014S/L1014F genotype.ConclusionsThis study confirmed that the early part of sporogony is most affected by temperature fluctuations, while environmental factors affect mosquito survival. The impact of insecticide resistance on malaria infection and vector survival needs to be assessed separately for mosquitoes with different resistance mechanisms to fully understand its implications for currently available vector control tools and malaria transmission.

Consequences of larval competition and exposure to permethrin for the development of the rodent malaria Plasmodium berghei in the mosquito Anopheles gambiae

“…[5,51]). Similarly, that permethrin exposure did not affect the longevity of individually reared mosquitoes corroborates studies that found no or negative effect of insecticide on post-infection survival following larvicidal (Bti) [19] or pyrethroid exposure [15,52]. However, in our experiment mosquitoes that were exposed both as larvae and as adults survived longer than unexposed ones, if they had been reared with competition.…”

“…However, exposure to permethrin at either larval or adult mosquitoes reduced both the prevalence of infection and the mosquitoes' infectiousness. These results corroborate several studies that found lower Plasmodium infection prevalence after adult mosquitoes were exposed to deltamethrin (a pyrethroid) [14,15,52], bendiocarb (a carbamate) or DDT (an organochlorine) [53] (but see [54]). Our findings also complement these results by showing that exposure at larval and adult stages, even at a very low dose, have similar effects on infection prevalence.…”

Effects of sublethal doses of an insecticide on the vectorial capacity of the malaria vector Anopheles gambiae

“…In addition, while we found no effect of permethrin exposure on mosquitoes reared individually, those reared in competition had an increased longevity when they were exposed both as larvae and as adults. These results do not support previous studies that found no or negative effect of insecticide on post-infection survival following larvicidal (Bti) (95) or pyrethroid exposure (128,237). Indeed, our results suggest that the insecticide may positively interact with mosquito immunity (as suggested by the results on prevalence) and alleviate the costs of the infection.…”

“…These results are in accordance with several studies that found reduction of Plasmodium infection prevalence after adult mosquitoes were exposed to deltamethrin (pyrethroids) (128,223,237), bendiocarb (carbamate) or DDT (organochlorine) (119) (but see ( 238)). Our findings corroborate and complements these results by showing that exposure at both larval and adult stages -even at very low dose-have similar effects on infection prevalence.…”

Putative Pleiotropic Effects of the Knock-Down Resistance (L1014F) Allele on the Life-History Traits in Anopheles Gambiae.

“…Gametocyte-infected mosquitoes must survive long enough to become infectious and transmit the sporozoites to a new host [60]. So, one of the key factors modulating malaria transmission is the vector longevity post blood feeding.…”