What substance would be used to handle a pest problem involving adult insects specifically?

The correct answer is based on the specific target of the substance in managing pest problems. Adulticides are chemicals specifically formulated to target and kill adult insects. This makes them particularly effective for controlling populations of existing adult insects that may be causing issues, whether that be damage to crops, structures, or as vectors for diseases.

In contrast, acaricides are designed to deal with mites and ticks, which are technically arachnids rather than insects. Larvicides focus on targeting larvae, which are the immature life stages of insects, preventing them from maturing into adults. Lastly, insecticides is a broad category that encompasses a wide range of products intended to kill insects at various life stages, including adults, but the term does not specifically denote the targeted action that adulticides do. Thus, when specifically dealing with adult insects, adulticides are the appropriate choice due to their targeted formulation.