Impact of Amaranthus spp. weed presence on the population abundance of Spodoptera cosmioides (Lepidoptera: Noctuidae) in genetically engineered soybean crops

Abstract

The introduction of herbicide-resistant and Bt crops has led to significant disruption in weed and insect pest communities. Using pheromone-baited traps, we assessed the impact of varying levels of Amaranthus infestation on the population abundance of S. cosmioides in both Bt and non-Bt soybeans. Additionally, we monitored the abundance of S. cosmioides and other leaf-chewing larvae in these soybeans employing the vertical beat sheet method. There was no difference in the number of S. cosmioides adults captured by pheromone-baited traps in Bt and non-Bt soybeans. Traps placed in plots with high Amaranthus levels captured 68.3% more S. cosmioides males than those with low Amaranthus presence. Similarly, a higher number of S. cosmioides larvae were recorded in soybean plots with high Amaranthus levels. In Bt soybean, the larvae of S. cosmioides were the most abundant Lepidoptera, although its populations were surpassed in the second crop season by R. nu. In non-Bt soybean, C. includens was the dominant species throughout both crop seasons, and its larval abundance was unaffected by Amaranthus infestation levels. The presence of green bridges may facilitate the colonization of S. cosmioides in soybean crops, as adults and larvae were more abundant in soybeans with high levels of Amaranthus infestation. Moreover, the influence of other key species such as C. includens negatively affected the abundance of S. cosmioides in non-Bt soybean. A combined approach of constant monitoring and management of difficult-to-control weeds is crucial for managing polyphagous pests.