MID-INFRARED SPECTROSCOPIC PROFILING OF HEMOLYMPH ACROSS LARVAL INSTARS IN FALL ARMYWORM, SPODOPTERA FRUGIPERDA (SMITH, 1797) (LEPIDOPTERA: NOCTUIDAE)

Abstract

The circulatory system in insects serves an essential role in coordinating physiological processes, particularly homeostasis, defense, heat transfer and gaseous exchange. Hemolymph acts as functional analogue to vertebrate blood and lymph. The present study employed Attenuated Total Reflectance–Fourier Transform Infrared (ATR FTIR) spectroscopy to characterize hemolymph biochemical composition of fall armyworm (Spodoptera frugiperda) larvae across third, fourth, and fifth instars. Hemolymph samples collected from thoracic region were analyzed in mid-infrared region (4000-400 cm-1). Changes in corresponding wavenumber along with functional groups and molecular vibrations revealed instar-specific variations in crucial biomolecules comprising carbohydrates, proteins, lipids and nucleic acids. The single bond region (3700–3300 cm⁻¹) corresponds to progressive elevation in hydroxyl and amide A bands, indicating accelerating hydration and protein concentration during larval development. The double bond region (1750–1500 cm⁻¹) exhibited distinct carbonyl (C=O) and amide I and II peaks, reflecting increased lipid deposition and protein synthesis for subsequent utilization in later stages (pupal and adult development). Carbohydrate and phospholipid signals in the fingerprint region (1500–600 cm⁻¹) reflect biochemical complexity associated with larval growth and development. These distinct age-related spectral patterns demonstrate compositional shifts across each developmental instar, establishing ATR-FTIR spectroscopy as a rapid, non-damaging, reagent-free tool capable of identifying age-specific changes in biochemical complexities for precise assessment in S. frugiperda larvae.