Recently purchased 1500 ladybugs to take care of my petunias in the window boxes. Within a few hours they had all disappeared! I've found 4 of them! I'm being overrun with aphids. Why do you think they all disappeared?NE Ohio

The nurseries sell ladybugs every spring to release. Their instructions are to overhead water so the foliage is wet because the lady bugs will be thirsty after being stuck in a box all winter. Continue to provide a water source, like a shallow saucer with a paper towel in it.

Release them in the evening near the aphid infestation. If they find somehow your accommodations to be inadequate, they will fly away. Thirst seems to be the biggest reason they fly away immediately.

We've mail-ordered ladybugs twice. One shipment was held up over the weekend in a post office side-track, so that half of them were DOA and more died in the next two days. The other arrived on time, and still contained a lot of dead bugs and delayed casualties. The survivors of both contingents dispersed in the greenhouse and performed very poorly. It seems a wasteful and cruel practice, with very little to show for it.
Our local garden center sells nematodes.
Me, I collect praying mantises when I get the chance.

wind may have dispersed your Ladybugs - if there are aphids around they will find them

had a aphid invasion on my desert rose - maybe 100+ on a few plants - was about to spray my plants with insecticidal soap - but a single ladybug was perched on a leaf - held off spraying until next day

on the next day - aphids were gone

mature ladybugs will clean out an aphid invasion - so will the ladybug larvae