What are key characteristics of contact insecticides?

• A. Remain on leaf surfaces, break down from sunlight and washing, effective ~2-3 days depending on weather
• B. Are systemic and move through the plant
• C. Are absorbed by the soil and persist for weeks
• D. Are only effective indoors

Answer: (A)

Contact insecticides work by killing pests that touch the spray residue on the outside of the plant. They stay on leaf surfaces and do not move into or through the plant. Because they sit on the surface, they are continuously exposed to sunlight and rain, which break them down and wash them off. That makes their practical window of effectiveness short—about 2–3 days, though weather can shorten or extend this period.

This is why they’re described as surface-active and short-lived: their action depends on direct contact with the pest and on staying on the plant surface long enough to strike. They aren’t systemic, so they don’t move within the plant to reach pests hiding inside or in other plant tissues, and they aren’t primarily soil-absorbed with long-lasting persistence. They’re also commonly used outdoors on ornamentals and turf, not only indoors, so the indoors-only option isn’t accurate.