Which formulation is characterized by being always used dry and having active ingredients in a carrier?

The correct choice is dust, which is characterized by being applied in a dry form. Dust formulations typically consist of active ingredients combined with a carrier, which helps to facilitate their application and effectiveness. When using dust, the particles can easily cling to surfaces, allowing for effective pest control. This method is particularly useful for targeting pests that hide in cracks, crevices, or other hard-to-reach areas where liquid applications may not penetrate.

In contrast, granules are also a solid formulation but are often larger in size and can be designed to dissolve or release the active ingredient slowly when moistened, which is different from the immediate application of dust. Powders, while similar, may not always imply a dry application as they can sometimes be mixed with water for use. Fumigants generally exist in gas form and are used for other applications like structural pest control or treating soil, making them unsuitable for comparison with dry formulations.

Thus, the characteristics of dust, including its dry application and the presence of a carrier with active ingredients, make it the correct answer.