3.1. Study area and hut construction
Ten circular huts were constructed in Edo Gojolla Kebele (the lowest political administrative population unit in Ethiopia), Adami Tulu Judo Kombollcha District, East Showa Zone, Oromia Regional State, Ethiopia, located at about 160 Kms from Addis Ababa, along the road to Hawassa. The huts, each having a sprayable surface of 12.56 m2 (2π X 2 m x 2 m), were constructed on land owned by local farmers interested to construct the huts (cost covered by the project) and later on to own the huts at the end of the trial. The huts were made of mud bricks and thatched roofs similar to the residential huts in the area. The interior of each hut wall was divided to four equal surfaces and each surface was plastered to have one of four surface types: rough (one layer of mud), smooth (two layers of mud), cow dung (cow dung over two layers of mud) and painted (a layer of paint over a layer of lime, applied to 2ndsmooth layer of mud). After construction was completed; the huts were locked and left to dry under natural environmental conditions.
3.2. Insecticide products evaluated
- Fludora® Fusion WP-SB56.25 is a new insecticide formulation for Indoor Residual Spraying. The formulation is a Wettable Powder in water soluble bags (WP-SB) available in 100g sachets. The product contains two active ingredients: 500 g/kg clothianidin + 62.5 g/kg deltamethrin. The application rate of the product is 200 mg clothianidin/sqm and 25 mg deltamethrin/sqm.
- Clothianidin WG70: containing 700g/kg clothianidin - applied at 200 mg/sqm
- FICAM WP80: containing 800 g/kg FICAM - applied at a rate of 400 mg/sqm.
3.3. Insecticide spraying
Nine huts were randomized into three experimental groups (each group having three huts) and the remaining tenth hut was left as an untreated control. The walls were checked for absence of insecticidal activity prior to spraying of the insecticides. A spraying operator having long time experience undertook the spraying on December 5, 2017 following Standard Operating Procedures and WHO manual [5, 11, 12]. One group of the experimental huts was sprayed with Fludora® Fusion WP-SB56.25, the second with FICAM WP80 and the third with Clothianidin WG70 following the instructions of the manufacturer (Bayer). The control hut was sprayed with equal volume of water. The walls were sprayed to attain dosages as per the manufacturer’s recommendation using the standard Hudson Xpert pump with 8002E nozzles with a volume of 10 L. One sachet containing a formulation of an insecticide was placed in the pump containing 10 L of water and was allowed to dissolve, followed by agitation of the pump to ensure adequate mixing. The pressure inside the pump was adjusted to 55 psi after which the products were applied via indoor residual spraying (IRS) with the maximum application rate amounting to 40 mL spray/m2. Calibration of the pumps was done prior to spraying to obtain uniform and good quality spraying for the target dose. Protective clothing, goggles and gloves were provided to the spray man for general safety. Sachets and waste water were disposed according to WHO guidelines [5, 12].The huts were kept free of animal and human contact until the end of the trial.
An insectary colony of An. arabiensis DebreZeit strain, susceptible to all insecticides and maintained at the Aklilu Lemma Institute of Pathobiology, Addis Ababa University was used for evaluation of the residual efficacy of Fludora® Fusion. WHO cone bioassays  were carried out a month after spraying and thereafter on monthly intervals for 12 months. On the day of the bioassays, the floor of the huts was wetted with water to create favorable room temperature and relative humidity conditions for the trial. Three cones were attached on each surface type at different heights by using small nails. Ten unfed, 2-4 days old, female mosquitoes were transferred to each cone using mouth aspirator (a separate aspirator was used for each insecticide/treatment) and exposed for 30 minutes. After 30 minutes of exposure, the mosquitoes were transferred to clean holding cages and then supplied with sugar solution by moistening a pad of cotton. Cages were kept in polythene bags with damp cotton inside to create favorable temperature (+ or – 25oC) and humidity (above 60%) for the survival of mosquitoes and placed in an insecticide free room. Knockdown was recorded at 60 minutes and mortality at 24 hours, 48 hours and 72 hours holding time post-exposure in order to cover delayed mortality effects as well.
Data was entered into Microsoft Excel spread sheets from which percentages of knockdown and mortality were determined and results interpreted according to WHO . As mortality in the control groups was above 5% no Abbott’s formula  based mortality correction was made. The Excel data was transferred to IBM SPSS Statistics 20 and fitted to generalized linear models statistics to compare mortality effects for Anopheles arabiensis mosquitoes 24 hours-post exposure to the insecticides, each insecticide on four different types and heights, and time since insecticides sprayed.
This study was reviewed and approved by the Institutional Review Board (IRB) of Aklilu Lemma Institute of Pathobiology, Addis Ababa University. Permission to conduct the study was obtained from local government officials in Adami Tulu Judo Kombollcha district. Huts were constructed on lands owned by local farmers after obtaining their consent. Consent was obtained from the farmers, owning the lands, after they had been clearly informed about the study objectives, methodology, anticipated benefits, and discomforts.