Cut off Behavior of Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae) in Soybean (Glycine max (L.) Merrill) Seedlings

Abstract

In addition to destroying the leaves, stems, pods, and grains of soybean (Glycine max), Spodoptera frugiperda larvae may also have the cut off behavior in the seedlings close to the ground, harming the establishment of the soybean crop. Therefore, this study aimed to evaluate the consequences of the fall armyworm attack by adopting the cut off behavior, which has been similarly documented for black cutworm (Agrotis ipsilon) in newly emerged soybean plants. The treatments were five levels of infestation with 0, 5, 10, 20 and 40 larvae per m 2 . Three variables were assessed: (1) stand (relationship between attacked and initial number of plants), (2) types and amounts of injured structures, such as hypocotyl (embryonic shoot), and the cotyledons (seed leaves), and (3) level of defoliation. The variables were collected every 24 hours until the pupal stage. Additionally, the final stand of the seedlings was quantified, with the highest injury intensity observed in the plots that contained the highest number of larvae. In the second experiment, the dynamics of movement and attacks of plants by S. frugiperda larvae at the following times of the day: 07:00, HIGHLIGHTS• Spodoptera frugiperda has a cut off behavior on soybean seedlings.• Soybean injury occurs as a density-dependent response.• From the third instar there is an increasing feeding behavior of the larvae.• Seedlings with more advanced stages present injuries only on the leaves.