Sunflowers as a trap crop for reducing soybean losses to the stalk borer Dectes texanus (Coleoptera: Cerambycidae)

Larvae of Dectes texanus LeConte cause significant losses to soybean production in the American High Plains by girdling the stalks of mature plants at their base, causing them to lodge. The authors demonstrated that cultivated sunflowers can reduce rates of D. texanus infestation in adjacent soybean fields because adult females prefer sunflower over soybean for feeding and oviposition. Since females do not avoid ovipositing in plants already containing their own eggs or those of conspecific females, sunflower plants can accumulate multiple eggs, and subsequent larval combat typically results in the survival of only one. In west central Kansas, planting one half of a center pivot irrigated field to sunflower in 2004 significantly reduced infestation of soybean plants in the other half of the field within 200 m of the crop border. Beyond 200 m from the sunflowers, the rate of soybean infestation increased significantly. Planting sunflowers in the non-irrigated corners of a center pivot irrigated soybean field in 2005 reduced D. texanus infestation of soybeans by 65% compared with a control field without adjacent sunflowers. Surrounding a 0.33 ha soybean field with six rows of sunflowers in 2006 reduced soybean infestation to < 5% of plants, compared with 96% of sunflower plants. These results reveal that sunflowers can reduce D. texanus infestation in adjacent soybeans by acting as an 'ovipositional sink'. Further research is warranted to determine the optimum crop area proportions and spatial configurations that will maximize the efficacy of a sunflower trap crop to reduce soybean losses due to D. texanus-induced lodging.