Physonata Unipunctata Continued

I am enjoying an accidental picking of the last of one of my delphiniums. I purchased three 3" pots @.99 cents each last spring. This year's flowers were beautiful. However, the bind weed also thrives in that part of the yard. I pulled this part of the plant off as I was dead-heading and weeding around the delphiniums. Today I found two gallon pots of delphiniums in white and lavender on clearance for $2.97 each, so I sprang for them. The more, the merrier.

I believe I am winning the war against my physonata unipunctata, otherwise known as the one-spotted tortoise beetle, or bergamot beetle. I found only four crawling on the leaves. Below is a picture of a ravaged stalk, showing some of the damage. The damage is less visible in the second photo, but many of the leaves are eaten. There are some blossoms. I am hoping that I have curtailed the reproductive process a bit so that next year's plants will be healthier.

The presence of the larvae on new plantings makes me wonder. Were the eggs always present in the soil, waiting for the right host to come along? What would they have  fed on before the monarda, if they have always been around? How far might they have traveled to get to my plants? Did they come from the nursery in the form of eggs in the soil when I bought my plants? I saw an internet reference to the physonata unipuncta eggs in Minnesota soil in 1917, but not much else.