Population dynamics of early larval instars, late instars and pupae of Anopheles spp . in open field trials exposed to water-dispersible granule (WDG) of Bti . Arrows indicate the date of treatment. Trial period from December 26th 2012 to January 23rd 2013. White horizontal bars indicate no significant difference between treatment and control tubs, blue bars do (dark blue: α = 0,05; light blue α = 0,10). Days with precipitations are indicated and amount of rainfall is given in millimeters.