Resistance to the larvicide temephos and altered egg and larval surfaces characterize salinity-tolerant Aedes aegypti

Abstract

Aedes aegypti, the principal global vector of arboviral diseases and previously considered to oviposit and undergo preimaginal development only in fresh water, has recently been shown to be capable of developing in coastal brackish water containing up to 15 g/L salt. We investigated surface changes in eggs and larval cuticles by atomic force and scanning electron microscopy, and larval susceptibility to two widely-used larvicides, temephos and Bacillus thuringiensis, in brackish water-adapted Ae. aegypti. Compared to freshwater forms, salinity-tolerant Ae. aegypti had rougher and less elastic egg surfaces, eggs that hatched better in brackish water, rougher larval cuticle surfaces, and larvae more resistant to the organophosphate insecticide temephos. Larval cuticle and egg surface changes in salinity-tolerant Ae. aegypti are proposed to respectively contribute to the increased temephos resistance and egg hatchability in brackish water. The findings highlight the importance of extending Aedes vector larval source reduction efforts to brackish water habitats and monitoring the efficacy of larvicides in coastal areas worldwide.

Preimaginal development ofAedes aegyptiin brackish water produces adult mosquitoes with thicker cuticles and greater insecticide resistance

“…albopictus in the Jaffna peninsula oviposit and undergo preimaginal development not only in FW, but also coastal brackish water (BW) collections of up to 15 g/L salt, e.g. in fishing boats, beach debris and coastal wells [6][7][8][9][10][11]. The ability of both Aedes vectors to develop in coastal BW has been confirmed in other countries [11], including the USA [12,13].…”

“…in fishing boats, beach debris and coastal wells [6][7][8][9][10][11]. The ability of both Aedes vectors to develop in coastal BW has been confirmed in other countries [11], including the USA [12,13]. FW, BW and saline water are respectively defined as containing <0.5, 0.5 -30 and >30 g/L salt [6,14].…”

“…albopictus larvae in the Jaffna peninsula are more salinity-tolerant than the corresponding FW-derived larvae from mainland Sri Lanka [6], because of the absence of a barrier to gene flow in Ae. aegypti within the small (1100 km 2 ) Jaffna peninsula and the peninsula's relative geographical isolation [11]. Altered cuticle protein composition, increased transcription of genes concerned with cuticle synthesis and cuticle thickening were prominent changes in fourth instar (L4) larvae of BW-adapted Ae.…”

“…Altered cuticle protein composition, increased transcription of genes concerned with cuticle synthesis and cuticle thickening were prominent changes in fourth instar (L4) larvae of BW-adapted Ae. aegypti [11,15]. Importantly, the changes in BW Ae.…”

“…Importantly, the changes in BW Ae. aegypti L4 were accompanied by reduced susceptibility to temephos [11], which is the principal larvicide used worldwide for controlling Aedes vectors [2][3][4].…”