Maybe it just needs some time.
Simply because of their vast numbers and limited mobility, the many hundreds of larvae of the ladybug are much more efficient aphid killers than the winged adult. The adult phase is mainly designed to fly around and distribute the eggs for future offspring. Of course they probably stop for a snack every now and then.
"As a larva it will gorge on about 400 aphids..."
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Wooly aphids can be tough because they secrete a honeydew that results in a fungal growth that gives them additional protection. Keep in mind that most any insecticides you use will not target the pests specifically, but also the beneficials.
Regards,
Matt