Influence Of Temperature On The Growth, Development And Susceptibility Of Anopheles Gambiae (S.L.) Mosquitoes To Pyrethroids.

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2023-02

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University of Ghana

Abstract

Background: Anopheles mosquitoes are responsible for transmitting malaria and lymphatic filariasis. They are among the notable vector species for their crucial role in transmitting malaria. The survival of the vector is of great interest as it affects its ability to transmit diseases. The biology and ecology of mosquitoes are strongly dependent on ambient temperature. The mosquito's life cycle includes four stages: egg, larva, pupa and adult. Indeed, the rearing temperature of the immature stages (egg, larva, and pupa) can significantly impact the completion of the life cycle, the overall fitness of the adult, and ability to transmit disease. In recent years, global warming and possible future warmer climate have prompted many studies to focus on the effects of elevated temperatures on both the morphology and the biology of various species, including vectors. Despite the importance of temperature variability on An. gambiae (s.l.) mosquito's development and survival, there is still the need to explore how and whether or not elevated temperatures associated with climate change is likely to reduce or increase the vector's population dynamics by modifying the life cycle, reduce the efficacy of insecticides, and increase the expression of metabolic enzymes in An. gambiae (s.l.) mosquitoes. Objective: This study aimed to investigate the influence of elevated temperatures on the growth and development of An. gambiae (s.l.) mosquitoes, and the effectiveness of pyrethroid insecticides in such higher temperatures. Methods: Anopheles gambiae (s.l.) eggs were obtained from colonies established in the laboratory and were incubated, hatched and reared under eight temperature regimes (25, 28, 30, 32, 34, 36, 38 and 40 °C) using climate-controlled incubators (RTOP-1000D, Zhejiang, China), with photoperiod of 12:12 (L:D) and 80 ± 10% relative humidity. Larvae were fed 10 mg of TetraFin goldfish flakes (Tetra Werke, Melle, Germany). All adults were fed with a 10% sugar solution soaked in cotton wool. In addition, female mosquitoes used to estimate fecundity and longevity were blood-fed using a guinea pig on day four (4) post-emergence. Larvae were monitored daily for development to the next stage. The time to pupation, pupation success, number of adults produced, and sex ratio of the newly emerged adult was recorded. Molecular identification of An. gambiae (s.l.) mosquitoes was done using polymerase chain reaction (PCR) to identify the composition of sibling species in the An. gambiae complex. Larval survival and adult longevity were monitored every 24 hours, and data were analyzed using Kaplan-Meier survival analysis. Furthermore, analysis of variance (ANOVA) was used to assess the relationship between temperature and development time, time to pupation, length of the gonotrophic cycle, biting rate and fecundity. Kruskal-Wallis test was also used to assess the relationship between temperature and pupation success, pupal mortality, the number of adults produced, and sex ratio. Digital images of larvae, pupae, adult wings and proboscis were captured using stereo microscope with inbuilt camera (Leica EZ4 HD, Leica Microsystems Limited, Switzerland) and body parts were measured using Leica Application Software, version 3.4.0 (Leica Microsystems Limited, Switzerland). Data on larval, and pupal weight and size, adult weight, size and proboscis length were log-transformed and analyzed using ordinary least square (OLS) regression with robust standard errors. In addition, three to five-day-old non-blood-fed An. gambiae (s.l.) mosquitoes were used for insecticide susceptibility test following the WHO bioassay protocol. Batches of 20 – 25 non-blood-fed female adult An. gambiae (s.l.) mosquitoes from each temperature regime (25 – 32 °C) were exposed to two pyrethroid insecticides (0.75% permethrin and 0.05% deltamethrin). The knockdown rate after 60 min and mortality at 24 h were recorded. The levels of four metabolic enzymes (MFO, GST, α-EST and β-EST) were examined in both mosquitoes that were not exposed and those exposed to pyrethroids. mosquitoes and provides helpful information for modelling vector population dynamics in a future warmer climate.

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PhD. Public Health

Keywords

Influence, Temperature, Growth, Development, Mosquitoes, Susceptibility

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