In the present study, we demonstrated that the larval breeding habitats in the three sites vary distinctly with regard to their physico-chemical characteristics and microbial abundance.
Previous studies have demonstrated that the physico-chemical characteristics [30–32] of the larval breeding habitat determine the larval and pupal density, the size and number of emerged adults and the survival of both larvae and adult mosquitoes. Thus, the mosquitoes in the study sites could also differ in their fitness (e.g. size, longevity, fecundity) and capacity to support and transmit the malaria parasite [8, 10]. Previous studies have shown that different species of mosquitoes maintained and reared in low food environments had a reduced longevity, smaller body size and lower vectorial capacity [8, 9, 31, 33, 34]. Most mosquito life traits (fitness) are affected by environmental factors, and specifically the breeding habitat [8–10, 35, 36].
The present observation of an increased total number of emerged mosquitoes for the larvae that were reared in water collected from Asendabo is an indicator for a higher suitability of that larval habitat. For this site, two parameters that stand out include a high bacterial abundance and increased oxygenation. Previous studies have established that bacteria in the breeding habitat constitute the main food source for larvae enhancing larval growth and the productivity and survival of the adult mosquitoes [8, 9, 17]. Studies have also demonstrated that higher dissolved oxygen favours the development of Anopheles mosquitoes [37, 38].
In this study wing size of the adult female mosquitoes was measured because the wing size is also an indicator for the suitability of the larval breeding environment. Our data revealed there is a marked variation in the wing size between the mosquitoes originating from different breeding sites with the Asendabo site yielding mosquitoes with the largest wing compared to Jimma and Wolkite. A similar variation in the wing size among the mosquitoes grown in different larval habitats was reported earlier for Anopheles stephensi  and Anopheles darlingi [8, 39]. It was concluded that such variation in the wing size is closely linked to the nutrient availability in the habitat [8, 9].
Wing size is directly correlated with survival of adult female mosquitoes, i.e., the mosquitoes with longer wing showed a higher longevity than short winged mosquitoes [9, 12, 40, 41]. Comparison of the survival of the mosquitoes reared with water from the three sites in the present work was supported by the above observation. For instance, the mosquitoes reared in the water from the Asendabo site that had the longest wing displayed the longest survival.
Previously we have demonstrated that the depletion of some midgut gene proteins including the FN3D1, FN3D3 and GPRGr9 genes markedly shorten the longevity of female An. arabiensis . In the present study, we assessed whether the variation between breeding habitats may affect the gene silencing effect. Our survival data revealed that the effect of gene silencing was not affected by variation in the larval breeding site, i.e. for all the study sites the FN3D1 treated mosquitoes had a similarly reduced survival rate compared to the control LacZ group. Thus, the variation in breeding sites does not affect the gene silencing effect on reducing the longevity of An. arabiensis mosquitoes. Gene silencing induces mosquito mortality by disrupting the midgut homeostasis , which is evidenced also in the present work where a higher bacterial load was observed in the FN3D1 silenced mosquitoes as compared to the LacZ silenced mosquitoes.