Sublethal concentrations of anthelmintic drugs (albendazole and levanide) induce insecticidal effects and midgut ultrastructural changes in Spodoptera frugiperda (Lepidoptera: Noctuidae)

Abstract

The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae) is a globally serious pest of maize and various cultivated plants. Rapid resistance development in certain pest populations underscores the urgent need for new, effective insecticides. The present study aimed to investigate the insecticidal potential of two anthelmintic drugs (albendazole and levanide) as alternative safer tools against this destructive lepidopteran pest. The toxicity and survival response of FAW larvae to both drugs were evaluated. Subsequently, the histopathological and ultrastructural effects of the drugs’ sublethal concentration (LC₂₅) on the midgut of third-instar larvae after 48 h of treatment were studied. The larval survival percentage of control group was 100 %, whereas the LC₅₀/48 h of albendazole and levanide treatment caused the survival percentage to drop to 51 % and 45 %, respectively. Furthermore, the sublethal concentration (LC₂₅) of the drugs reduced the survival of larvae by dramatically disrupting the S. frugiperda midgut’s ultrastructure and hindering insect development. Interestingly, both drugs at LC₂₅/48 h damaged the peritrophic matrix releasing cell apical protrusions and apocrine secretions into the midgut lumen and breaking down microtubules leading to cellular hypertrophy. The study also found deterioration in mitochondrial structure. The most noticeable changes were an irregular nuclear envelope and nucleus with condensed chromatin and increased autophagy and apoptosis. Comparatively, the difference in cytotoxicity between drugs depended on their mode of action. The present findings confirm that both anthelmintic drugs even at sublethal concentrations have significant insecticidal potentials and might be an alternative, safer environmental tool in managing FAW larvae.