Ultra-structural and physico-chemical characterization of eggs and egg hairs (setae) of the new invasive pest, fall armyworm, Spodoptera frugiperda (J. E. Smith) in India: A first report.

Abstract

In this study, we report first time in India on the morphology, ultra-architectural pattern of the chorion in the egg and egg hair (setae). Further, physico-chemical characterizations of egg hairs (setae) were studied in the new invasive pest, fall armyworm, Spodoptera frugiperda. The egg is dome shaped with flattened base and curves upward to a broadly rounded point at the apex. HR-SEM micrographs revealed the surface ultrastructure of eggs chorion and shows structural elements of a marked rosette of petals surround the micropyle followed by micropylar rosette region around the micropyle plate. There was a small single micropylar opening along with 9 micropylar rosette cells and 13 micropylar rosette zones present near to the micropylar pit. In the egg the first order ribs were absent, but around 58-60 numbers of second order ribs were present. All the ventral and lateral cells of the eggs are connected by 19-22 cross striae and not forming a grid pattern, but joints with the longitudinal ribs at several of angles and totally 1,277-1,495 convex cells present at the egg's surface. The physico-chemical characteristics of egg hairs were studied using Fourier transform infrared (FT-IR) and thermogravimetric analysis (TGA) analysis. TGA results show that three weight losses occurred at 142, 418, and 880°C, respectively. FT-IR confirms the presence of amides, sulfoxide, and nitro compounds in egg hairs (setae).