The dectes stem borer, Dectes texanus LeConte, is a longhorned beetle native to the High Plains and southeastern United States. Its wild host plants are mostly annual weeds such as ragweed, Ambrosia spp., and cocklebur, Xanthium strumarium L., although other plants also may be attacked. Cultivated sunflowers have always been a preferred host plant, and it emerged as a pest of soybeans shortly after the expansion of soybean cultivation in the 1960s. It now infests commercial soybeans in at least 12 states and cultivated sunflowers throughout the High Plains, except for the most northern regions.
Adult beetles are gray to bluish-gray and 3/8 to 3/4 inches (1.0 to 2.0 cm) long (Figure 1). Antennae have dark, transverse bands and are longer than the body. Adult beetles are active during the day but secretive, spending much of the time hiding under leaves within the plant canopy. Sometimes they may be seen flying and running around on plant surfaces. When approached, beetles either take flight or fall to the ground, feigning death.