class MyController < ActionController::Base
  before_filter :restrict_to_development, :only => [:user_report]

  def index
    ...
  end

  def user_report
    ...
  end

  protected
    # this method should be placed in ApplicationController
    def restrict_to_development
      head(:bad_request) unless RAILS_ENV == "development"
    end
end

class MyController < ActionController::Base

  if RAILS_ENV == "development"
    def index
      #...
    end
  end
end