Morphological and biochemical effects of insect growth regulators; Diflubenzuron and chromafenozide on the cotton leaf worm Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae)

Abstract

he Egyptian cotton leafworm Spodoptera littoralis (Boisduval, 1833) is considered one of the most destructive agricultural lepidopterous pests in subtropical and tropical regions. It is a polyphagous insect and it is known to destroy more than 29 plant hosts from other crops and vegetables and 100 different species of plants. Insect growth regulators (IGRs) have been considered as the possible alternative agents of synthetic insecticides for controlling S. littoralis pest. In the present study, two IGRs were chosen; the chitin synthesis inhibitors, diflubenzuron (Dimilin®) and the ecdysone agonist, chromafenozide (Virtu®). The present study evaluated and assessed the expected side effects of the two IGRs, Dimilin® and Virtu® on the susceptibility, biological, biochemical, histological, and ultrastructural changes of the target organs, ovarioles and larval corpora allata of S. littoralis. The study determined the median lethal concentration (LC50) of these IGRs, and then applied the LC50(1.3 & 3 ppm Dimilin®) and (0.1 & 0.1 ppm Virtu®) to the S. littoralis 2nd and 4th instar larvae, respectively. Then, the study recorded any morphological features, biological effects, quantitative and qualitative analysis of larval haemolymph and tissue homogenate to estimate some biochemical parameters (protein, carbohydrates and lipids as well as ADH, AO α-Est and β-Est), histopathological as well as ultrastructural abnormalities to the ovarioles and larval corpora allata.