Which statement is true of dust pesticides?

The statement that some dusts can remain active against pests indefinitely is true, as certain dust formulations are designed to remain effective for extended periods without significant degradation. This long-lasting efficacy is due to their chemical composition and the mode of action; for example, dust pesticides may adhere to pests' bodies and continue to be effective as long as they remain undisturbed. When pests come into contact with these dusts, they can be exposed to the active ingredient over time, leading to prolonged pest control.

Other options have limitations. While some dusts can provide a physical barrier or may help with dehydration, these are not universal characteristics applicable to all dust pesticides. Dusts may offer a barrier effect, but they are primarily intended to facilitate contact with pests rather than to work solely by exclusion. Regarding the effectiveness of dusts in air ducts, while they can be used in such environments, their efficacy may be limited due to airflow and difficulty in achieving even distribution.