There are few insecticides labeled for indoor use, and topical sprays tend to work faster for pests like aphids and mites since they are intended to work on contact with the pest. Mealybugs can be more difficult to eradicate (especially if they have infested roots as well; not all species do), but using systemic insecticide (something the plant's roots absorb from soil and move into stems and leaves) isn't always an option if the plants needing treatment are food crops like vegetable seedlings. Hydroponic systems likely cannot make use of a systemic option since the roots are not in soil (potting mix).

You'll need to check the product label on any pesticide under consideration to verify it can be used indoors and how often it needs to be applied. (Horticultural oil and insecticidal soap, for instance, both tend to be applied every 1-2 weeks, but it can vary depending on the pest and the plant's tolerance. Labels will note if certain plant species are known to be sensitive to that spray.)

Buying and releasing ladybugs or another beneficial/predatory insect isn't usually practical for home indoor growing, both because they are sold in large quantities intended for covering large areas (like commercial greenhouses and conservatories), they may not survive well in indoor conditions (lower ambient humidity, often), they may not stay on the plants and could instead wander off to fly to windows and lamps, and their perishable nature requires rapid shipping that adds to their cost. Sometimes the species sold may also be non-native, and we don't want to release (more) non-native insects into the local ecosystem when the plants go outside.

For plants that can be placed under a faucet without the potting mix falling out of the container, the foliage can be sprayed with plain water in a sink or shower to knock off most of the aphids, mealybugs, and mites. A lower population is easier to keep under control using topical pesticides than one that is treated while they are still abundant.

Miri