Exploring integrated strategies to control oviposition and larval development in mosquitoes in Northern Tanzania

CHAPTER 1 1.0. GENERAL INTRODUCTIONBesides services, ecosystems can also provide disservices (von Dhren and Haase, 2015).A common disservice is the emergence of mosquitoes from freshwater habitats.Larval and pupal stages of the life cycle of members of the dipteran family Culicidae (mosquitoes), develop in aquatic habitats (WHO, 2003).After emergence as adults, mosquitoes not only are a nuisance but in many (sub)tropical and Mediterranean regions they also play a key role in the transmission of diseases to both humans and animals (Becker et al., 2010).Malaria, dengue, lymphatic filariasis, chikungunya, zika and yellow fever are among the diseases transmitted by vector mosquitoes in humans (Lee et al., 2018;Tolle, 2009).Morbidity and mortality caused by mosquito borne diseases are far greater than those caused by other vector borne diseases (Tolle, 2009).For this reason, mosquitoes have been put forward as the most dangerous animals to humankind (Becker et al., 2010).For example, every year more than 337 million people become ill and more than 669,000 people die from mosquitoborne diseases worldwide (WHO, 2020).Mosquitoes are found throughout the world, except in permanently frozen areas.Their larvae can colonize a wide range of aquatic habitats including temporary and permanent, highly polluted as well as clean, large, or small, stagnant, or flowing water.Even the smallest accumulations such as water-filled buckets, coconut shells, flower vases, old unused tires, bromeliads, hoofprints or leaf axils and tree cavities can act as suitable larval habitat (Chadee et al. 1998, Kahamba et al. 2020, Kitching., 2014). Mosquito life cycle and biologyMosquitoes have four life stages in their lifetime namely, adult, egg, larval, and pupal stages.Unlike female mosquitoes, male mosquitoes do not bite and therefore do not transmit pathogens of diseases (WHO, 2003).Soon after eclosion adult female mosquitoes mate, and they do this once in their lifetime.Mated female mosquitoes thereafter find a blood meal by biting animals or humans which is important to complete egg development (Becker et al., 2010).After sucking blood, mosquitoes rest for two to three days before oviposition to digest the ingested blood but also for egg development.Usually, they rest on different places inside and outside houses such as on walls, under furnitures, on clothes hanging in the house, on plants, in trees, on the ground, or in other cool dark places (WHO, 2003).All mosquitoes need aquatic habitats for their development (Becker et al., 2010).After blood meal mosquitoes such as those in the genus Anopheles and Culex find suitable aquatic habitats to lay eggs.Oviposition sites vary from small hoofprints and rain pools to streams, swamps, canals, rivers, ponds, lakes, rice fields, Other mosquito borne diseasesDengue disease is caused by the dengue virus (arbovirus) from the genus Flavivirus (family Flaviviridae) which is transmitted by female mosquitoes of the species Aedes aegypti and Aedes albopictus (Hertz et al., 2012).Although dengue is endemic to more than 100 countries in the world, the South-East Asian region (i.e., Bangladesh, India, Bhutan, Thailand, Sri Lanka, Korea, Nepal, Indonesia, etc.) and the Western Pacific region (i.e., China, Mongolia, Papua New Guinea, New Zealand, etc.) are most affected (WHO, 2017b).The fact that majority of dengue cases are asymptomatic, and many are misclassified ensures that the number of actual global dengue cases is underreported (WHO, 2017b).About 2.38 million cases and 1,032 deaths were reported by the World Health Organization (WHO) in the Americas (i.e., USA, Canada, Venezuela, Cuba, Mexico, Chile, etc.) in 2016, while the Western Pacific region reported more than 375,000 cases (WHO, 2017b).Despite its global importance, the extent of dengue burden in Africa remains unknown due to lack of data, and the same is true for the burden in terms of yellow fever, chikungunya, filariasis and zika cases (Weetman et al., 2018).However, Burkina Faso, a country in the WHO Africa region, reported 1,061 dengue cases in 2016 (WHO, 2017b).Aedes aegypti, A. albopictus and Culex quinquefasciatus are also main vectors of the chikungunya virus, an arbovirus from the genus Alphavirus (family Togaviridae) (Hertz et al., 2012).Chikungunya cases are unusual and normally occur in outbreaks which have been reported in 60 countries in Africa, Asia, the Americas and Europe and the number of those infected is variable.The disease is characterized by fever and pain in the joints as symptoms (WHO, 2017c).Mosquitoes also transmit parasitic nematodes which cause lymphatic filariasis.The disease is well established in tropical and subtropical areas where it is endemic to 72 countries including those in Africa, Asia, the Indian subcontinent, the western Pacific Islands, Latin America, and the Caribbean (WHO, 2022).About 90% of the estimated 120 million people living with filarial pathogens are infected by the nematode worm Wuchereria bancrofti.Brugia malayi and Brugia timori also cause infection particularly in Asia (WHO, 2022).Although lymphatic filariasis is transmitted by various mosquito genera such as Culex, Anopheles, Aedes and Mansonia, the mosquito C. quinquefasciatus is the principal vector (Fox et al., 2013).One third of people infected with the disease live in India, one third in Africa and the remainder in South-East Asia, the Pacific, and the Americas (Becker et al., 2010).It is noteworthy that C. quinquefasciatus is a member of C. pipiens species complex which is a group of sibling morphospecies.The species complex comprises of C. pipiens, C. quinquefasciatus, Culex australicus, and Culex globocoxitus.Fig. 3 shows the modelled current global geographical ranges of habitat suitability for A. aegypti and A. albopictus mosquitoes, which also shows the current global distribution ranges of 2003 to 2005

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