Deltamethrin-Mediated Effects on Locomotion, Respiration, Feeding, and Histological Changes in the Midgut of Spodoptera frugiperda Caterpillars

Abstract

Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is the main pest of maize crops, and effective methods for pest management are needed. The insecticidal efficacy of deltamethrin was evaluated against S. frugiperda for toxicity, survival, locomotion, anti-feeding, and histological changes in the midgut. Concentration-mortality bioassays confirmed that deltamethrin (LC₅₀ = 3.58 mg mL^-1) is toxic to S. frugiperda caterpillars. The survival rate was 99.7% in caterpillars not exposed to deltamethrin, decreasing to 50.3% in caterpillars exposed to LC₅₀, and 0.1% in caterpillars treated with LC₉₀. Spodoptera frugiperda demonstrated reduced mobility on deltamethrin-treated surfaces. Deltamethrin promoted a low respiration rate of S. frugiperda for up to 3 h after insecticide exposure, displaying immobilization and inhibiting food consumption. Deltamethrin induces histological alterations (e.g., disorganization of the striated border, cytoplasm vacuolization, and cell fragmentation) in the midgut, damaging the digestive cells and peritrophic matrix, affecting digestion and nutrient absorption.

Keywords: anti-feeding effect; histopathology; repellency; respiration rate; survival; toxicity.

Figure 1

Survival curves of Spodoptera frugiperda caterpillars exposed to different lethal concentrations of deltamethrin, subjected to survival analyses using the Kaplan–Meier estimator log-rank test (χ² = 64.55, df = 4, p < 0.001).

Figure 2

Behavior response of Spodoptera frugiperda caterpillars caused by deltamethrin. (A) Representative tracks showing the walking activity of S. frugiperda over a 10-min period on filter paper arenas half-impregnated with deltamethrin (upper half of each arena). Red tracks indicate high walking velocity; green tracks indicate low (initial) velocity. (B) Resting time and distance walked of S. frugiperda subjected to deltamethrin (control, LC₅₀, and LC₉₀ estimated values) for 10 min. Treatments (mean ± SEM) differ at p < 0.05 (Tukey’s mean separation test).

Figure 3

Respiration rate of Spodoptera frugiperda caterpillars exposed to deltamethrin (control, LC₅₀, and LC₉₀ estimated values) for 3 h. Treatments (mean ± SEM) differ at p < 0.05 (Tukey’s mean separation test).

Figure 4

Anti-feeding effect caused by deltamethrin on Spodoptera frugiperda caterpillar. (A) Leaf section (20 × 20 mm) treated with distilled water and insecticide submitted to color binarization (black and blue) with identification and quantification of area consumed. (B) Leaf area consumed by S. frugiperda exposed to deltamethrin (control, LC₅₀, and LC₉₀ estimated values). Treatments (mean ± SEM) differ at p < 0.05 (Tukey’s mean separation test).

Figure 5

Light micrographs of the midgut of Spodoptera frugiperda caterpillars 3, 6, 12, and 24 h after exposure to deltamethrin. (A–E) Apical portion of digestive cells showing sequential effects with increase in vacuolization. (F–J) Basal portion of digestive cells showing sequential effects with increase in vacuolization. (K–O) Details showing sequential effects in the peritrophic matrix. Epithelium (Ep), lumen (L), peritrophic matrix (►), cell protrusion (*). Control (A,F,K).