Effect of critical temperatures on mortality and cuticle composition of Plodia interpunctella larvae: Insights from GC–MS analysis and SEM imaging

The Indian meal moth, Plodia interpunctella Hübner (Lep.: Pyralidae), is a significant global pest of stored products, particularly in temperate regions. This study investigated the impact of various temperatures (25, 50, 55, and 60 °C) over different durations (5, 10, 15 and 20 min) on the mortality and cuticle layer of third instar P. interpunctella larvae. Hexane solvent separated the cuticle layer of 3rd instar larvae treated at critical temperatures; Bis (trimethylsilyl) acetamide and Trimethylsilyl chloride were added for derivatization before injection into the GC–MS. Additionally, SEM imaging was used to observe the epicuticle surface of treated larvae under critical temperatures. The findings showed a direct relationship between increasing temperatures and the mortality rate of 3rd instar larvae, with complete mortality occurring in 20 min at 50 °C, in 15 min at 55 °C, and in just 10 min at 60 °C. Moreover, with an increase in temperature and exposure time, the weight of the larvae decreased significantly. GC–MS analysis unveiled that the waxy layer contained sixteen fatty acids within P. interpunctella cuticles; it was observed that as temperatures increased, there was a significant reduction in fatty acid levels. SEM imaging also revealed that rising temperatures led to a dramatic decrease in cohesion within the epicuticle layer; altering its physical and chemical structure caused dehydration, ultimately leading to death. These results suggest that utilizing critical temperatures for short durations can effectively control P. interpunctella populations.