Above photos by Joan Allen, University of Connecticut.
The tobacco budworm, Heliothis virescens, is found throughout the eastern U.S. (and in other places!). It does not overwinter in northern states so it’s usually seen late in the season after it moves northward, primarily on wind currents in the adult moth stage.
Eggs are laid singly on leaves of host plants. Favored hosts are tobacco and its relatives including geranium and another common name of this insect is the geranium budworm. There are many other occasional hosts including field crops, vegetables and ornamentals. The little hatchling shown in the photos was on a geranium leaf.
The egg was noticed while inspecting the leaf under a microscope and movement within it caught my eye. I noticed that the caterpillar was chewing its way out of the egg so I spent 5-10 minutes watching the whole process. Once emerged, the caterpillar moved its head back and forth then turned around and returned to consume the rest of the egg, a nutritious first meal. A bit of feeding may take place on leaves, leaving holes, but this is enroute to the flower buds where feeding causes damage that results in flowers with holes in the petals.
As the caterpillar progresses through five to six instars it develops white stripes down its sides and reaches a length of approximately 1 inch. The color can be quite variable and is influenced by the color of the food source as shown below!
The adult is a light brown moth with three darker transverse bands on the forewings. The hind wings are mostly off white with a darker band on the edges. Wingspan is 1.1-1.4 inches.
The best control measure in the home garden is to check for damage to buds and for caterpillars beginning in late summer and remove any that are found by hand.