Assessing Toxicity and Some Biochemical Alterations for Nano-formulation of Emamectin Benzoate in Spodoptera littoralis

Abstract

Emamectin benzoate (EMB) is a commonly used insecticide against Spodoptera littoralis, but its EC formulations are intolerance to light and temperature. This study aimed to develop and characterize a nano-emulsion of EMB (nano-EMB), assess the toxicity and biological effects of EMB and nano-EMB on S. littoralis, and investigate their interaction with certain enzymes. The results demonstrated the stability of nano-EMB with no phase separation during freeze-melt cycles, shaking and centrifugation.
Characterization of nano- EMB using Transmission Electron Microscopy (TEM) revealed spherical droplets with size (39.0 -72.0 nm), and a zeta potential of 38.5 mV. The toxicity tests showed that, nano- EMB was 13 times more toxic to the 4th instar larvae of S. littoralis than EMB, with LC50 = 0.0014 and 0.0183 mg/l, respectively. The sub-lethal exposure to both EMB and nano-EMB affected the
development of S. littoralis and significantly decreased adult emergence, fecundity, fertility, and longevity despite increased adult deformation; the highest effect was recorded in the larvae treated with LC50 of nano-EMB. Additionally, EMB caused a significant decline in acetylcholinesterase activity, which was low in larvae treated with LC25 or LC50 (0.029 and 0.032 μM/mg/min, respectively),
compared with that treated with LC25 or LC50 of nano-EMB (0.038 and 0.037 μM/mg/min, respectively) While no significant changes were observed in α-esterase activity. Conversely, nano-EMB at LC50 significantly increased β-esterase activity (7.11 μM/mg/min) compared with the other treatments. The findings here suggest that nano-EMB could serve in integrated pest management programs, offering lower application rates and improved pest control efficacy.