Soybean stem borer

Dectes spinosus is a species of beetle belonging to the order Coleoptera and the family Cerambycidae. This insect is a significant pest in soybean production, recognized primarily for the damage caused by its larvae, which burrow into the stems and remain protected from most surface-applied pesticides for the duration of their development.

While soybean is the primary host crop, the pest can also thrive on several wild plant species, including common ragweed and cocklebur. This wide range of hosts creates challenges for pest management, as these weeds act as reservoirs for the beetle throughout the season, facilitating its persistence within agricultural landscapes.

The biology and lifecycle of the pest are typically completed in one generation per year. Adult beetles emerge during the summer months, coinciding with the flowering stages of soybeans. They feed on leaf petioles and stem tissues, after which females lay eggs. The larvae hatch and bore into the pith of the stem, feeding internally as they develop.

The damage caused by this pest is primarily physiological and structural. By feeding on the internal pith, larvae disrupt nutrient and water transport, often leading to reduced yield. Furthermore, late-season larval activity involves girdling the stem from the inside at the soil level, which causes plants to lodge or fall over, making mechanical harvesting extremely difficult.

Effective control measures require an integrated approach. Cultural practices such as crop rotation, removing host weeds from field borders, and early harvesting can significantly reduce infestation levels. While chemical control targeting adult beetles is possible, it must be timed precisely with the adult emergence window to prevent egg-laying before the larvae move into the stems.