Proposed Economic Threshold for Diceraeus melacanthus (Dallas) in Maize Under an Early Intercrop Cultivation System.

Abstract

The Antecipe® system, in which maize is sown between soybean rows while soybean plants are still in the reproductive stage, reduces the production cycle of the soybean-maize crop system and, consequently, mitigate climatic risk for second-crop maize. However, the coexistence of both crops can intensify the 'green bridge,' favoring outbreaks of Diceraeus melacanthus. Thus, this study evaluated the host preference of D. melacanthus and the damage caused by different population densities to support management strategies in this system. The preference test was conducted in the greenhouse using cages (1.5 × 0.5 m) containing senescing soybean and maize at the VE stage, infested with ten adult D. melacanthus. Evaluations were carried out over three consecutive days at three times per day. The field experiment followed a completely randomized design with four stink bug densities (0, 1, 2, and 4 insects/m) in 6 × 4 m cages. When maize reached the VE stage, insects were introduced, and damage was assessed. Preference tests indicated a predominance of stink bugs on soybean, especially during the warmest periods of the day, whereas their activity on maize was higher in the early morning. In the field experiment, maize plants exposed to 2 and 4 stink bugs/m showed the highest damage levels, and yield reduction was observed at the density of 4 stink bugs/m; however, with 2 stink bugs/m, yield was statistically equal to both 1 and 4 stink bugs/m (intermediate yield), which could be a turning point from plant tolerance to plant compensation in the damage curve. Therefore, we propose that 2 stink bugs/m should be adopted as a more conservative (yet preliminary) economic threshold (ET) for maize cultivated in this system. Such ET must now be validated in farm conditions, under different climatic conditions (different regions), with different maize varieties.