Histopathological effects of Diflubenzuron and Chromafenozide (IGRs) on egg development in the cotton leafworm Spodoptera littoralis (Boisd) (Lepidoptera, Noctuidae)

Abstract

The present study was undertaken to investigate the possible pathogenic impacts of the LC50 of the two insect growth regulators: the chitin synthesis inhibitor, Dimilin® (Diflubenzuron), and the ecdysone agonist, Virtu® (Chromafenozide) on the ovarian tissue of adult female Spodoptera littoralis. Therefore, the LC50 (1.3 & 3 ppm of Dimilin® and 0.1 ppm of Virtu®) were applied to the 2nd and 4th larval instars, respectively. The meroistic polytrophic ovariole of S. littoralis is divided into a terminal filament, a germarium and a vitellarium; the germarium contains the oogonia and the follicular cells that surround the oocytes to form the ovarian follicles in the vitellarium. The ovarian follicles of treated F1 females with Dimilin® exhibited vacuolization, stuffing of follicular sheath, loss of vitellin and degeneration of many cell components of follicular epithelium and oocytes. These obvious signs of damage were increased when using 4th larval instars treatment than the 2nd.Also, damage was pronounced in the ovarioles of the Virtu® treated F1 females. Ovariole growth was stunted and vitellogenesis and chorion formation were inhibited. So, this work shows the high potency and efficacy of the two IGRs on developed ova of S. littoralis.