Fitness Costs of the Glutathione S-Transferase Epsilon 2 (L119F-GSTe2) Mediated Metabolic Resistance to Insecticides in the Major African Malaria Vector Anopheles Funestus

Abstract

Metabolic resistance to insecticides threatens malaria control. However, little is known about its fitness cost in field populations of malaria vectors, thus limiting the design of suitable resistance management strategies. Here, we assessed the association between the glutathione S-transferase GSTe2-mediated metabolic resistance and life-traits of natural populations of Anopheles funestus. A total of 1200 indoor resting blood-fed female An. funestus (F0) were collected in Mibellon, Cameroon (2016/2017), and allowed to lay eggs individually. Genotyping of F1 mosquitoes for the L119F-GSTE2 mutation revealed that L/L119-homozygote susceptible (SS) mosquitoes significantly laid more eggs than heterozygotes L119F-RS (odds ratio (OR) = 2.06; p < 0.0001) and homozygote resistant 119F/F-RR (OR = 2.93; p < 0.0001). L/L119-SS susceptible mosquitoes also showed the higher ability for oviposition than 119F/F-RR resistant (OR = 2.68; p = 0.0002) indicating a reduced fecundity in resistant mosquitoes. Furthermore, L119F-RS larvae developed faster (nine days) than L119F-RR and L119F-SS (11 days) (X2 = 11.052; degree of freedom (df) = 4; p = 0.02) suggesting a heterozygote advantage effect for larval development. Interestingly, L/L119-SS developed faster than 119F/F-RR (OR = 5.3; p < 0.0001) revealing an increased developmental time in resistant mosquitoes. However, genotyping and sequencing revealed that L119F-RR mosquitoes exhibited a higher adult longevity compared to RS (OR > 2.2; p < 0.05) and SS (OR > 2.1; p < 0.05) with an increased frequency of GSTe2-resistant haplotypes in mosquitoes of D30 after adult emergence. Additionally, comparison of the expression of GSTe2 revealed a significantly increased expression from D1-D30 after emergence of adults (Anova test (F) = 8; df= 3; p = 0.008). The negative association between GSTe2 and some life traits of An. funestus could facilitate new resistance management strategies. However, the increased longevity of GSTe2-resistant mosquitoes suggests that an increase in resistance could exacerbate malaria transmission.

An Experimental Hut Evaluation of PBO-Based and Pyrethroid-Only Nets against the Malaria Vector Anopheles funestus Reveals a Loss of Bed Nets Efficacy Associated with GSTe2 Metabolic Resistance

“…The L119F-GSTe2 mutation was genotyped to assess how the glutathione S-transferase gene, GSTe2, impacts the performance of the bed nets. An allele specific PCR [27,28] was used to detect the three genotypes of the L119F-GSTe2 mutation (homozygote resistant:RR, heterozygote resistant: RS and homozygote susceptible: SS). The PCR was carried out using 10 mM of each primer and 1 µL of gDNA as template in 15 µL reaction containing 10× Kapa Taq buffer A, 0.2 mM dNTPs, 1.5 mM MgCl2, 1 U Kapa Taq (Kapa Biosystems, Wilmington, MA, USA).…”

“…This suggests that L119F-GSTe2 mutation likely contributes to an increased malaria transmission as every additional bite increases the chance of sporozoite to be passed to the populations. This is particularly a concern as 119F-RR resistant mosquitoes have also been shown to live longer [27,28] and to have a greater vectorial capacity to transmit Plasmodium [12]. However, it is noticeable that the impact of L119F-GSTe2 on blood feeding ability is mainly seen for Olyset Plus and Olyset LLINs impregnated with permethrin but present an opposite effect for PermaNet 3.0 and 2.0 both impregnated with deltamethrin.…”

Influence of GST- and P450-based metabolic resistance to pyrethroids on blood feeding in the major African malaria vectorAnopheles funestus

“…However, as already discussed above, we cannot exclude that the absence of influence observed for L119F-Gste2 gene might also be related to the low number of L119F-RR mosquitoes used in the present study. This latter hypothesis seems moreover reinforced by results of previous studies showing L119F-GSTe2 mutation [23] and CYP6P9a -R resistance gene [37] affecting An. funestus fecundity in the same way.…”

“…The L119F-GSTe2 mutation was genotyping using gDNA extracted from carcasses of field-collected strain and following allele specific PCR diagnostic assay previously described [23]. The primers sequences are given in table S1.…”

“…funestus mosquito, one study reported that a GST-based metabolic resistance caused by a leucine to phenylalanine amino acid change at codon 119 in the glutathione S-transferase epsilon 2 (L119F-GSTe2) [22], has a detrimental impact on An. funestus fitness as field mosquitoes exhibited a reduced fecundity and slower larval development but an increased adult longevity [23]. On the other hand, a new DNA-based assay was recently designed for cytochrome P45O-mediated resistance (the CYP6P9a-R in An.…”