Pathogenicity of Purpureocillium lilacinum and Clonostachys rosea Against Fall Armyworm (Spodoptera frugiperda) Under Laboratory Conditions

Background: Fall armyworm, Spodoptera frugiperda (J.E. Smith) threatens staple crops across Africa. Integrating entomopathogenic fungi into Integrated Pest Management (IPM) offers a sustainable alternative to sole reliance on insecticides. This study quantified the pathogenicity of Purpureocillium lilacinum and Clonostachys rosea against S. frugiperda under controlled conditions. Methods: Second-fifth instar larvae and eggs were exposed to 1×107, 1×108, and 1×109 conidia mL-1 of each fungus; sterile water served as control. Mortality was recorded over 3-9 days after treatment (DAT); feeding reduction was measured gravimetrically. Larval mortality was analyzed with GLMs/GLMMs (binomial-probit); feeding reduction by ANOVA/Tukey; LD50 and LT50 were estimated from dose-response models. Results: Mortality increased with dose and time, and decreased with larval stage. Peak larval mortality reached ~44% for P.lilacinum and ~49% for C. rosea at 1×109 conidia mL-1 by 9 DAT. Egg mortality was concentration?dependent (up to 82% and 88% for P. lilacinum and C. rosea, respectively, at 1×109 conidia mL-1). Feeding reduction reached 60-74% in early instars at the highest dose. Early instars were consistently more susceptible than late instars. Model outputs indicated significant effects of concentration and time; interaction concentration×time was significant, whereas fungal species×concentration was not. Our findings supported the initial hypothesis. Mortality and feeding reduction increased with higher fungal concentrations and longer exposure times, and younger instars were consistently more susceptible than older instars. While both P. lilacinum and C. rosea were pathogenic, differences between species were minor compared to the effects of dose and instar stage. These outcomes validated the formulated hypotheses, and reinforce the potential of these native fungi as candidates for IPM. Conclusions: Native P. lilacinum and C. rosea display dose-, stage-, and time-dependent pathogenicity and feeding suppression against S. frugiperda. These species are promising candidates for IPM; field validation and formulation optimization are the next steps.