Following are a series of 4 photographs depicting various aspects of rice borers. The first photograph shows a rice stalk with the typical orangish lesion on the leaf sheath where a borer entered the plant. The eggs hatch and very small (about 1/16th inch long) borers move behind the leaf sheath where they begin to feed and eventually bore into the stem. This is the only time foliar insecticides are effective on them. Once they have bored into the stem we cannot get to them. Dermacor seed treatment is labeled and effective against borers.
The next photograph is of a mid-instar sugarcane borer, the borer that has become the most common borer in rice over the past several years. It is distinguished from the rice stalk borer and Mexican rice borer by the dark head capsule and dots on its back. This one was about an inch long.
The third photograph is a closeup of the throacic region of a rice stalk borer. Above the second and third legs there are two dots. They are the base of a hair (seta) like the others on the body, but because I shot the photograph head on you cannot see the hairs. This was taken with a camera so I know they are visible with a good hand lens. This is the definitive distinguishing characteristic to separate the rice stalk borer from the Mexican rice borer. The rice stalk borer has two setae above each leg while the Mexican rice borer will have only one above each leg.
The borer in the bottom photograph is a very young rice stalk borer that could easily be mistaken for a Mexican rice borer. Normally the head capsule of the rice stalk borer is dark. This one may have recently molted and the head is still very light colored. The lines on its back are fairly continuous in contrast to the Mexican rice borer which has lines resembling a series of dashes.