1. INTRODUCTION
According to World Health Organization (WHO), vector control strategies
led to major reductions in malaria cases in many areas around the world
(WHO 2018). The scale-up of two principal tools, long-lasting
insecticidal nets (LLINs) and to a lesser extent indoor residual
spraying (IRS), have contributed up to 33 % reduction in malaria deaths
in Africa, the most affected continent, during the last decade
(Hemingway 2014).
For impregnating LLINs, the WHO currently recommends six pyrethroids and
for IRS, twelve insecticides, belonging to four classes of insecticides
(pyrethroids, organophosphates, carbamates and organochlorines) were
selected. Unfortunately, malaria vectors are developing resistance to
insecticides used in these tools, mainly to pyrethroids. Resistance to
this insecticide class is now widespread in Anopheles gambiaes.l. populations across sub-Saharan Africa (Dabiré et al. 2009, Ranson
et al. 2011). Mutations in para -type voltage-gated sodium channel
gene (Hemingway and Ranson 2000) providing high levels of
cross-resistance to pyrethroids and DDT that share the voltage-gated
sodium channel as a target site in mosquitoes that is known to be the
main mechanism resistance.
In West Africa, pyrethroid resistance in Anopheles mosquitoes is
mainly attributed to mutation in the sodium channel target site, the
L1014F kdr (Dabiré et al. 2009) while another L1014S mutation
originated from Kenya known as kdr -East (Ranson et al. 2000), was
recently detected in the same region, in An. arabiensispopulations from Benin (Djègbè et al. 2011) and in An. gambiae
s.s and An. coluzzii from Burkina Faso (Namountougou et al.
2013) as well as in An. gambiae s.s from Togo, West Africa
(Djègbè et al. 2018).
Insecticide resistance in malaria vector populations in Burkina Faso has
been reported as early as in the 1960s, when An. funestus andAn. gambiae s.l. (thereafter, An. gambiae s.s ) populations
showed reduced mortality to dieldrin and DDT (Coz et al. 1968, Hamon et
al. 1968). After, other studies have confirmed that resistance to DDT is
still prevailing at a high level in An. gambiae s.l populations
from Burkina Faso, where cross-resistance to pyrethroids due to thekdr L1014F mutation was also increasingly reported (Diabaté et
al. 2002, Diabate et al. 2004, Dabiré et al. 2009). Moreover,
cross-resistance to organophosphates and carbamates due toace -1R G119S was also detected, although at a
moderate frequency (Weill et al. 2003, Djogbénou et al. 2008, Dabiré et
al. 2009). Finally, in the humid savannas regions of South-West Burkina
Faso, a complex context of multiple resistance is established inAn. gambiae s.l. populations (Dabiré et al. 2008) with the
concomitant presence of kdr L1014F andace -1R mutation genes. This particularly
alarming situation constitutes a major impendence to the success of
current vector control strategies.
The use of the same chemicals (organophosphates and pyrethroids) in both
agriculture and public health could lead to a more rapid development of
resistance to these compounds (Gnankiné et al. 2013). It is known that
the trend towards insecticide resistance in malaria vectors is partly
linked to the current use of these chemicals for crop protection
(Diabaté et al. 2002, Gnankiné et al. 2013, Hien et al. 2017, Chabi et
al. 2018). According to Akogbéto et al. (2006), residues from
insecticide applied on crops can contaminate mosquito-breeding sites,
resulting in promoting insecticide resistance selection among mosquito
larvae .
Indeed, the population of Africa has more than doubled over the past 30
years, increasing the demand for food and intensifying agricultural
production to achieve food security (NEPAD 2013). According to the New
Partnership for Africa’s Development (NEPAD), 530 million of the total
African population (around 48 %) depend on agriculture activities and
this population expected to reach 580 million in 2020 (NEPAD 2013).
Agrochemical use has increased dramatically in recent years and has
resulted in an important reduction in crop losses (NEPAD 2013). At the
same time, the African continent has experienced the massive deployment
of long-lasting insecticidal nets (LLINs), the most widespread
intervention tool against malaria vector, and to a lesser extent indoor
residual spraying (IRS). In fine, the massive use of insecticides in
both agriculture and public health could establish a double pressure of
resistance selection in mosquito vectors. Cotton production remains a
crop that requires an important use of insecticides belonging to
Pyrethroids (PY) and Organophosphates (OP). Up to now, three cotton
pests management strategies have been adopted in some African countries,
particularly South Africa and Burkina Faso: i) conventional based on
systematic use of insecticides belonging to Pyrethroids,
Organophosphates and neonicotinoids classes, ii) organic when no
chemicals are used and iii) transgenic Bt-cotton (Bacillus
thuringiensis ) when OP and PY are not used in fields, except
neonicotinoids (Gnankine et al. 2018). Transgenic cotton (Btcotton) has been adopted as new agricultural practice that aimed at
reducing the insecticides amount and their frequency of applications but
also at increasing yields (Gnankine et al. 2018). Since 2016,Bt-cotton cultivation has suspended by the government of Burkina
Faso due to the poor quality of cotton fiber.
With respect to the insecticide resistance increase in diseases vectors,
WHO launched the Global Plan for Insecticide Resistance Management in
malaria vectors (GPIRM) in 2012 (WHO 2012). GPIRM comprises of five
activities (described as five ‘pillars’) spanning in the short, medium
and long term, aimed at controlling insecticide resistance to ensure the
continued effectiveness of current and future vector control tools to
prevent malaria transmission, morbidity and mortality (WHO 2012).
The current study aimed at assessing the impact of the three cotton
pest’s management strategies in different ecological settings;
conventional, organic and transgenic cotton growing areas on insecticide
susceptibility in the main malaria vector in Burkina Faso, West Africa.