 Another study concluded that insecticide use on cotton and corn during the years 1996 to 2005 fell by of active ingredient, roughly equal to the annual amount applied in the European Union.A Bt cotton study in six northern Chinese provinces from 1990 to 2010 concluded that it halved the use of pesticides and doubled the level of ladybirds, lacewings and spiders and extended environmental benefits to neighbouring crops of maize, peanuts and soybeans.Resistance evolves naturally after a population has been subjected to selection pressure via repeated use of a single pesticide.