A water-free process for converting initially non-larvicidal evaporation suppressant powder into a larvicidal variant possessing utility both for abatement of use by mosquitoes of an open water catchment as a successful breeding site, and for conserving water by suppressing the evaporation of water from the same catchment. Lauryl alcohol is used as a blending agent to facilitate even distribution of mosquito-specific entomopathogens, eg., spores of Bacillus thuringiensis variety Israelensis or Bacillus sphaericus, into the initially non-larvicidal evaporation suppressant powder. Cetyl alcohol and/or stearyl alcohol are the preferred monolayer-formers upon which effective evaporation suppression relies. For a variant larvicidal powder that lacks an effective evaporation suppression property, the same preferred monolayer-formers may be omitted from a blend of mosquito-specific pathogens, lauryl alcohol, and hydrated lime or, alternatively, acidified gypsum.