If you purchased a batch of ladybugs from your local garden store and they all died shortly after releasing them, it is most likely due to one of two reasons:
1.) You have recently sprayed with a pesticide that remains on your plants. Keep in mind, that many synthetic pesticides breakdown slowly and can persist in the environment for days, or even weeks. If you must spray, select natural pesticides — insecticidal soap — that are short-lived in the environment, or specific to the target pest. For example, Bacillus thuringiensis (Bt-k) will control caterpillars, such as cabbage worms and gypsy moths without harming their natural enemies.
2.) You received a batch of ladybugs that have been stored for too long. Unlike most beneficial insects, live ladybugs are gathered twice per year (late winter/ early June) and stored in custom refrigerators prior to shipment. The longer they are stored the weaker they become and the higher the mortality rate will be. Ladybugs that have been kept for too long will often appear healthy during release, but die shortly after.
Note: Unlike most garden centers and box stores, we “walk” our ladybugs prior to shipment to ensure that only healthy beetles are shipped out, but some loss is still expected.
Hope it helps!