Toxicological, Biochemical and Histological Studies on the Fall Armyworm, Spodoptera frugiperda Treated with Five Insecticides

Saleh, H.A., S.F. Abd El-Rahman, M.A. Batt and H.R.K. Ali. 2024. Toxicological, Biochemical and Histological Studies on the Fall Armyworm, Spodoptera frugiperda Treated with Five Insecticides. Arab Journal of Plant Protection, 42(4): 489-496. https://doi.org/10.22268/AJPP-001280 Fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) is one of the most important, invasive, and destructive pests. It was reported for the first time on maize plants in 2019 in upper Egypt. A bioassay was conducted to evaluate the toxicity of 5 insecticides (Protecto 9.4% WP, Pesover 90% SP, Punkron 20% EC, Uphold 36% SC and Full 48% EC) against 2nd and 4th instar larvae of this pest under laboratory conditions. All tested insecticides were more efficient against the 2nd instar larvae than the 4th instars. Punkron was the most efficient pesticide against the 2nd instar larvae, with LC50=0.0039 g/L, whereas Uphold showed higher toxicity than the other insecticides against the 4th instar larvae (LC50=0.0524 g/L) 5 days after treatment. The effect of the tested insecticides on the activities of acetylcholine esterase (AChE), carboxylesterase (CE), glutathione S-transferase (GST) and Alpha & beta esterase enzymes was determined. All tested insecticides induced the activity of AChE and CE in the 4th instar larvae. On the other hand, the insecticides decreased GST activity, while increased the activity of Alpha & beta esterase enzymes in the same instar larvae, except for the insecticide Full (Chlorpyrifos). All insecticides induced histological alterations (e.g., structure of the muscle layers, disorganization in the epithelial cells, and cell fragmentation) in the midgut, damaging the digestive cells and peritrophic matrix, affecting digestion and nutrient absorption. The tested insecticides in this study may play a prominent role in the integrated management program of the fall armyworm. Keywords: Spodoptera frugiperda, insecticides, bioassay, biochemical activity, histology