Soybean Stem Borer
Egg - The yellow egg is elongate, narrowed at both sides, and about 1.5 mm long.
Larva - There are four larval instars varying in length from 1.5 to 15 mm. The larval body is spindle-shaped, creamy white, legless and appears corrugated. Color plate.
Pupa - The pupa, about 15 mm long, is yellowish when first formed but later turns dark brown.
Host Plants - Known hosts of the soybean stem borer include cocklebur, ragweed, several other weeds, and soybeans.
Damage - There is some evidence that a small yield decrease may result from larval feeding within the plant; however, most damage occurs when the immature borer cuts the plant stem from the inside. The insect-induced lodging is most severe on early-planted soybeans, especially in fields where soybeans were grown the previous season and where soybeans are not harvested soon after maturity.
Life History - This pest overwinters in North Carolina as mature larvae within tunnels in the stubble of soybeans, ragweed, cocklebur, and other weeds. Pupation occurs in late spring, and adults (beetles) emerge in early summer. About 5 days later, the beetles mate. Within 10 to 14 days, the females lay eggs in cavities along leaf petioles which have been chewed out by the beetles. When the eggs hatch, the larvae tunnel through petioles into the stem and feed on pith tissues until cold weather begins. Only one larva will mature in each soybean stem. This is apparently the result of cannibalism.
