Very interesting idea. We have sufficient volunteer ladybugs so we can’t help with your experiment. Have never seen an aphid in the field but we do see them on imported plants in the nursery. Outside, ladybugs reproduce at the base of young Ponderosa Pine trees, 6’ tall or less. When they hatch, the tree turns red and appears to be emitting smoke as they climb up the tree and fly away from the tips of the branches. An advantage of organic farming.
More relevent to your experiment, the overwhelming majority leave the property. Indeed, readings from 2 decades ago informed me that releasing ladybugs on one’s own property has little benefit as they tend to travel considerable distances before settling in. I have no experience with such things myself but that is certainly what we see from the natural swarms. Sounds like you have had different experiences when releasing small numbers. That could be the key difference. A crowded population may all depart while a sparce one may remain.
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