Oral Exposure to Cordyceps javanica Reduces Survival and Pupation of Spodoptera frugiperda and Alters Enzyme Activities and Immune-Gene Expression

Abstract

Simple Summary Spodoptera frugiperda (J.E. Smith, 1797), as a polyphagous leaf-feeding pest, poses a significant threat to economically important crops. Current research on the use of entomopathogenic fungi for the control of S. frugiperda has primarily focused on Beauveria bassiana (Bals.-Criv.) Vuill. 1912, Metarhizium anisopliae (Metschn.) Sorokin 1883, Metarhizium rileyi (Farl.) Kepler, S.A. Rehner & Humber 2014, and Cordyceps fumosorosea (Wize) Kepler, B. Shrestha & Spatafora 2017. However, research on how S. frugiperda responds to entomopathogenic fungal infections is still scarce, and only B. bassiana has been studied in this context. In light of this, the present study investigated the effect of Cordyceps javanica (Bally) Kepler, B. Shrestha & Spatafora 2017, a fungus with great biocontrol potential, on S. frugiperda, as well as the underlying mechanisms by which S. frugiperda responds to C. javanica infection. The results showed that feeding on C. javanica significantly reduced both the survival rate and the pupation rate of S. frugiperda. The immersion treatment had no significant effect on the survival, pupation rate, or female ratio of S. frugiperda. The C. javanica treatment continuously activated protective enzymes (immersion: SOD, POD, CAT; feeding: CAT) and detoxification enzymes (immersion: CarE; feeding: CarE, GST), but suppressed SOD and POD under feeding. Immune genes under immersion showed initial down- then up-regulation. Under feeding, gloverin followed this pattern, whereas attacin A and PGRP-LB were persistently down-regulated, and lebocin 4 showed the opposite trend (up then down). These findings provide a reference for the future control of S. frugiperda using C. javanica.