They also emit a sticky substance on the leaves, and sometimes sooty mold will grow on this. But whatever your problem, your treatment must have worked. It is possible that the pests were attracted to plants weakened by overwatering. Verbena plants do like a soil that drains well and one that is allowed to dry some between waterings. Good drainage, good air circulation and the correct light exposure go a long way in ensuring plant health.
Healthy plants stand a better chance against insects and diseases.
And water needs, of course, vary among plants. During the worst of this summer's heat and drought, once a week was not enough in some areas of my garden. The best way to tell if you're watering adequately is to use your fingers to test soil moisture 6 inches down. An inch of water will moisten a clay or loam soil 6 inches down. If your deep watering moistens the soil to that depth, once a week may be enough.