**1. Introduction**

Malaria remains a vector-borne disease of major public health significance globally [1]. It is estimated that about 198 million annual cases of malaria and a related 584,000 deaths occur worldwide [2]. Insecticide-based vector control in the context of integrated vector management (IVM) has a long-standing, proven record of preventing, reducing, and eliminating vectorborne diseases [3]. However, its continued efficacy is threatened by the selection of insecticide resistance in disease vectors coupled with the lack of sustainable financial resources [4],

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scarcity of requisite skills, and minimal or lack of collaboration between health and other relevant sectors to effectively monitor and manage it [3]. Evidence of insecticide resistance operationally undermining malaria vector control is mounting and is resulting in policy changes [5]. Monitoring and management of resistant disease vectors is essential to limit the selection and spread of insecticide resistance and to maintain the effectiveness of vector control [6]. Nevertheless, substantial challenges for implementation exist at country level. Thus, countries are encouraged to implement pre-emptive insecticide resistance management (IRM) strategies against malaria vectors according to the Global Plan for IRM (GPIRM) [7]. While IVM and IRM are the recommended approaches for combating vector-borne diseases and preventing the spread of resistance respectively, operational experience for both strategies is limited to relatively few countries. However, IVM provides a potential platform that could be exploited for enhanced national strategic IRM planning and deployment. This chapter reviews the distribution, mechanisms, and resistance management strategies in malaria vectors including the challenges experienced in operational settings. A framework of policies and strategies to facilitate the implementation of the GPIRM using the IVM platform is also presented and accentuates coordinated response among stakeholders and political commit‐ ment for effective policy execution within the context of national health systems.

#### **2. Literature search strategy**

Information sources for this review included all available data and accessible archived documentary records on malaria vectors and insecticide resistance. Structured literature searches of published, peer-reviewed sources using online scientific bibliographic databases were utilised to gather pertinent data. This was conducted via systematic literature search of Library catalogues and online electronic databases, particularly PubMed [8], the WHO Library Database [9], Google Scholar [10], the African Journals Online, the Armed Forces Pest Man‐ agement Board [11], and the research for life databases (AGORA, ARDi, HINARI, and OARE) were used to search for relevant literature. All digital electronic database searches for peerreviewed, published work used a combination of key search terms: 1) *Anopheles* malaria vectors complex and one of the following terms; 2) insecticide resistance; 3) resistance mechanisms; 4) resistance management; 5) impact of resistance; 6) malaria vector control; and 7) malaria epidemiology. Reference sections of all relevant articles were also reviewed to identify more literature. Additional non-peer reviewed literature were examined for information related to the subject. Articles that report biochemical and molecular tools for resistance monitoring were also retrieved. The inclusion criteria considered all manuscripts and publications in English language that report on selection of insecticide resistance in malaria vectors, causes and mechanisms of resistance, vector resistance and the epidemiology of malaria, integrated vector management (IVM), resistance patterns, and the impact in malaria vectors.

### **3. Classification and distribution of malaria vectors**

Mosquitoes belong to the family Culicidae in the order Diptera, class Insecta, phylum Arthropoda [12]. Culicidae is divided into three subfamilies Anophelinae, Culicinae, and

Toxorhynchitinae, and comprises approximately 3,450 recognised species of mosquitoes in 38 genera. The 34 genera are in the subfamily Culicinae, 3 in Anophelinae, and only 1 in Toxorhynchitinae [13]. Malaria vectors belong to the genera *Anopheles* (Cellia) Myzomyia and their global distribution has been recognised in six zoo-geographical regions: Palaearc‐ tic, Oriental, Australasian, Afro-tropical, Neoarctic, and Neotropical regions [14, 15]. Globally, about 465 species have been described in the genus *Anopheles* with seven subgenera that vary in species composition, i.e., *Anopheles* (182 species), *Baimaia* (one species), *Cellia* (220 species), *Kerteszia* (12 species), *Lophopodomyia* (six species), *Nyssorhyn‐ chus* (39 species), and *Stethomyia* (five species) [16]. However, the species able to transmit parasites that cause human malaria only belong to the subgenera, *Anopheles*, *Cellia*, *Kerteszia*, and *Nyssorhynchus* [17]. Only about 80 species are capable of transmitting malaria, 70 species are vectors of malaria under natural conditions and about 45 are of major significance [13]. The distribution of major vectors of malaria is determined mainly by temperature and the capacity of the air to desiccate the insect [18].

The global distribution of principal vectors of malaria is associated with 12 epidemiological zones of malaria: North America (*An. freeborni* and the *An. quadrimaculatus*), Central America (*An. albimanus, An. Aquasalis, An. pseudopunctipennis, An. argyritarsis*, and *An. darlingi,*), South America (*An. darlingi, An. albitarsis, An. Aquasalis, An. marajoara, An. nuneztovari*, and *An. pseudopunctipennis*), Afro-tropical (*Anopheles gambiae* Giles 1902 and *Anopheles arabiensis* Patton in the *An. gambiae* complex, and *Anopheles funestus* s.s. Giles 1900 in the *An. funestus* complex [19, 20] with *An. merus, An. melas, An. moucheti, An. pharoensis*, and *An. nili* implicated in transmission in localised areas [21, 22]), North Eurasian (*An. atroparvus*), Mediterranean (*An. atroparvus, An. labranchiae, An. messeae, An. sacharovi, An. sergentii*, and *An. superpictus*), Afro-Arabian (*An. arabiensis, An. pharoensis*, and *An. sergenti*), Indo-Iranian (*An. culicifacies* and *An. fluviatilis*), Indo-Chinese Hills (*An. dirus, An. fluviatilis,* and *An. minimus*), Malaysian (*An. campestris, An. donaldi, An. letifer, An. nigerrimus, An. aconitis, An. balabacencis, An. dirus, An. flavirostris, An. leucosphyrus, An. ludlowea, An. maculates, An. minimus, An. subpictus,* and *An. sundaicus*), Chinese (*An. barbirostris, An. lesteri, An. sinensis, An. aconitus, An. annularis, An. balabacensis, An. culicifacies, An. dirus, An. farauti, An. flavirostris, An. fluviatilis, An. koliensis, An. leucosphyrus, An. maculates, An. minimus, An. punctulatus, An. stephensi, An. subpictus,* and *An. sundaicus*), and Australasian (*An. farauti, An. punctulatus s.s.,* and *An. koliensis*) [15, 23]. Notably, malaria vector bionomics and their ecological variations have implications for their control.
