I would like to add three things to the previous responses.
1). After sanding either cork or balsa, "prime" the body with Gesso before painting. This is a white, water-based material that is brushed onto canvas to produce a flat surface for oil paints. It is available wherever artist supplies are sold.
2). Balsa bodies can be made more durable by coating the body, after painting, with 2-Ton (30 min) epoxy. Mix the epoxy and thin to the desired consistency with plain old rubbing alcohol, and paint on. I usually mix at a ratio of one part mixed epoxy to 1/2 part alcohol, but I may mix 1 part mixed epoxy with an equal part of alcohol. This makes a very thin mix. (Forget the "Old Wives Tale" that the water in the rubbing alcohol will turn the mix white: ABSOLUTELY NOT TRUE!)
3). Instead of a vertical face, slanting the face up and back will produce a diving bug, a la Charlie Cypert's Pencil Popper,which is a very effective "bug". A slope of about 15 degrees works quite well. This also works quite well for solid-body foam minnow patters; no, not "crease" minnows.