Agriculture is the primary economic activity within sub-Saharan Africa (SSA) (Berg, Blankespoor & Selod, 2018). In the East Africa region over 70 % of the population depends on agriculture (Roger et al., 2013; Shimeles, Verdier-chouchane & Boly, 2018). Over the last 30 year’s agriculture production in Africa has equalled that of South America, however, it is still below that of Asia (Loebenstein, 2010; Roger et al., 2013). One of the significant reasons associated with the lag in agricultural production in particular within SSA are insect vectors and associated viruses (Kreuze & Valkonen, 2017). Viral diseases when left uncontrolled account for production losses of between 30-100% (Mangeni et al., 2014; Worrall et al., 2015; Mwaipopo et al., 2018). In SSA insect vectors of agricultural importance include; aphids (Kinyanjui et al. 2016; Wamonje et al. 2017); whitefly (Bemisia tabaci and Trialeurodes vaporariorum) (Tajebe et al., 2014; Legg et al., 2014; Wainaina et al., 2017; Mugerwa et al. 2018), mealy bugs (Zeddies et al., 2001; Fermont et al. 2009; Yonow, Kriticos and Ota, 2017). Economic losses within smallholder farms, attributed to infestation by both the insect vectors viral diseases are estimated to be over 30 billion US dollars globally (Sastry & Zitter, 2014).
The insect vectors of interest are the whitefly: B. tabaci (Gennadius, Hemiptera: Aleyrodidae) and T. vaporariorum (Hemiptera: Aleyrodidae). Whiteflies are important agricultural pests with a global distribution (Anderson et al., 2004; Lapidot et al., 2014). Their agricultural importance is associated with damage caused during feeding on the plant phloem resulting in the production of honeydew (Colvin et al., 2006; Prijović et al., 2013; Eigenbrode, Bosque-Pérez & Davis, 2018). Honeydew serves both to reduce transpiration and as an inoculation point for saprophytic fungi, which grows over the leaf surface reducing photosynthesis (Colvin et al., 2006; Macfadyen et al., 2018). Secondly, they are associated with the transmission of over 600 viruses of which 100 are of significant agricultural importance (Jones 2003; Polston, De Barro, and Boykin, 2014; Lu et al., 2017). In SSA these viruses affect several important crops and in particular, cassava (Manihot esculenta Crantz) and sweet potato (Ipomea batata (L.)). Within this two crops, several whitefly-transmitted viruses have been reported which include; Cassava mosaic virus (CMV) (Legg, 1999; Naseem and Winter, 2016; Tairo et al., 2017) Cassava brown streak virus (CBSV) (Hillocks and Jennings, 2003; (Maruthi et al., 2005; Ndunguru et al., 2015; Alicai et al., 2016), Sweet potato chlorotic stunt virus (SPCSV), Sweet potato chlorotic fleck virus (SPCFV) (Ateka, et al., 2004; Tugume, et al., 2016; Mulabisana et al., 2018).
The agro-ecosystem within smallholder farms within the highlands of Kenya, are highly heterogeneous under mixed cropping system. Within the highlands of Kenya, maize (Zea May) is main crop and is intercropped with legumes such as common beans (Phaseolus vulgaris L.), cowpea (Vigna unguiculata (L.) Walp.), groundnuts (Arachis hypogaea L). Other crops found within this cropping system are, cassava, sweet potato and indigenous vegetables (Fig. 1). This form of cropping system is popular among smallholder farmers due to several advantages. Firstly, it reduces the risk of complete crop failure in cases of diseases or pest outbreaks. Secondly it maximizing the available land and manual labor (Mucheru-Muna et al., 2010).
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