Use immediately in most cases. One of the common sources of mortality in storage is desiccation. This can easily be avoided by placing the container of natural enemies in a plastic bag along with a wet sponge, and closing up the bag. These can be stored for up to 10 weeks, but need to be kept refrigerated and humid. This material is very stable and can be stored like an insecticide.
Natural enemies differ one from another in very important ways.
To use them successfully, you first must have a recommendation from a reliable source that a certain species is able to provide control of your pest in your crop. Second you must be sure that the supplier is selling you the species you want, not merely a related species. If is important that you verify that you are receiving what you order and that it is healthy. You should verify the number received by counting a small sample of the product and multiplying as needed to calculate the number per package. If you are not receiving full measure, contact your supplier for compensation or change suppliers.