This time of year we see insect pests throughout the garden. I have different tolerance levels for my vegetables than for the rest of the garden. Here on the lilies I may use a little insecticidal soap if there are hoards of bugs, or I may ignore a smattering of the pests. Beneficial ladybugs feed on whiteflies and aphids.
When you see an infestation of pests, consider whether the plant is weak and vulnerable to attack due to other conditions. I ask myself, are these lilies in too much shade, resulting in a loss of vigor, and therefore an easy target for pests? I should find time to move them to a sunnier location this fall.