Ultrasonic Exposure as a Potential Non-chemical Approach for Managing the Cotton Leafworm, Spodoptera littoralis (Boisduval): Developmental, Reproductive, and Digestive Physiological Responses

Abstract

The cotton leafworm, Spodoptera littoralis (Boisduval), is a major agricultural pest causing substantial economic losses in many crops. The present study evaluated the biological and physiological effects of ultrasound exposure on second- and fourth-instar larvae of S. littoralis under laboratory conditions. Developmental parameters, survival, reproductive performance, and digestive enzyme activities were assessed to determine the susceptibility of different larval stages to ultrasound treatment. Ultrasound exposure significantly affected the development and fitness of S. littoralis. In second-instar larvae, larval and pupal durations increased significantly, while pupation success, adult emergence, egg hatchability, and fecundity decreased to 65.0%, 40.0%, 48.5%, and 52.1% of the control, respectively. Malformation incidence increased markedly to 36.8%. In fourth-instar larvae, pupal duration was also prolonged, whereas larval duration was shortened. Pupation success, adult emergence, egg hatchability, and fecundity were reduced to 80.0%, 48.0%, 61.2%, and 68.4% of the control, respectively, accompanied by a malformation rate of 22.5%. Comparative analysis indicated that second-instar larvae were more susceptible to ultrasound treatment than fourth-instar larvae. No significant effect on sex ratio was detected in either larval stage. Biochemical analyses revealed significant inhibition of digestive enzyme activities following ultrasound exposure. Amylase, invertase, trehalase, and lipase activities were reduced by 40.5%, 34.5%, 45.0%, and 29.6%, respectively, compared with untreated controls. These reductions suggest impairment of nutrient digestion and metabolic efficiency, which may contribute to the observed developmental and reproductive disruptions. Overall, ultrasound treatment exerted pronounced adverse effects on growth, survival, reproduction, and digestive physiology of S. littoralis, particularly in early larval instars. These findings highlight the potential of ultrasound technology as an environmentally friendly component of integrated pest management programs targeting this economically important pest.