I was a city girl until a few years ago and although I liked observing nature with all the birds, insects, animals and plants, I never thought too much about moths. They were just night butterflies to me and that was it. Of course, I knew that butterflies grow from caterpillars, but it didn't occur to me that moths grow from caterpillars too and those caterpillars have to feed themselves with leaves before becoming moths. The only caterpillars I knew that ate leaves were those eating all the leaves on the trees around the block I was living in. I also knew about the silkworms which feed on mulberry leaves. That was actually all I knew about this part of nature. But all changed when I started living in the countryside. Everything in nature became clearer to me as I began to learn a lot about plants, birds, animals and, especially, insects. I learned about the various colors and shapes of the moths which come around the light bulb on the terrace on the summer nights. I also learned that I can find their caterpillars on my plants in the garden, feeding with their leaves, whether they are roses or zinnias or lilacs. But I would have never imagined that one of those moths' caterpillars were feeding on my geranium leaves and buds. Had I been more alert I should have known by now that those holes in my geranium's leaves and buds are made by specific caterpillars known as geraniums budworms or tobacco budworms.
This is the larvae of a small, nice, beige moth called Heliothis virescens or Helicoverpa virescens, which feeds especially on Nicotiana species. The budworms are one the most destructive pests of tobacco and cotton crops. Some of the common hosts are also petunias and geraniums, and occasionally, roses. The color of the larvae can differ from brown to green with yellow stripes. The coloration is determined by the type of plant the larvae are feeding with, but usually they are dark brown with yellow stripes. Their life cycle begins when the adult females lay single eggs on leaves or buds in late evening. Most of their activity takes place at dusk and stops at sunrise. Caterpillars become full grown in a month, then fall to the soil and pupate. Two generations of moths can grow during a season, then the larvae pupate during winter inside the soil and only very deep freeze can kill them. Two years ago I found this pupa covered with dirt which was stuck inside the frame of my greenhouse door. It seemed very much like a budworm pupae, but since all the sources I could find said that the tobacco worm pupate inside the soil, it might have been another worm's pupae. The geranium budworm pupate inside the ground, buried 4 to 6 inches deep inside a packed earthern cell which the catterpillar produces.
If these pests infest your containers, control is only achieved by changing the soil and sterilizing the pots before bringing the potted plants inside. Hand picking is also an option. Insecticides don't have much affect on them, but it can help. I have sprayed insecticide on all my infested geraniums, especially on their buds, and it worked for a while. Maybe regular spraying can help more. Prevention can be done by checking buds and leaves, to eliminate possible larvae.
Now I understand why my pansy geraniums never bloom like they used to: the budworms are eating their buds. I will have to pay more attention to them since they bloom in early spring, while they are still inside. But first, I'll change all the pots and soil, so there won't be any pupae left in there to eat my geraniums.
 - http://www.ext.colostate.edu/pubs/insect/05581.html
 - http://www.colostate.edu/Depts/CoopExt/4DMG/Pests/budworm.htm
 - http://www.weekendgardener.net/garden-pests/tobacco-budworm-050905.htm