Effectiveness of Entomopathogenic Fungi on Immature Stages and Feeding Performance of Fall Armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) Larvae

Maize is a major staple crop in China, and the sustainable productivity of this primary crop has been recently threatened by fall armyworm (FAW), , invasion. The five fungal isolates, sp. BM-3 and SE-2-1, SE-10, CTD-24, and ZK-5 were assessed for their efficacy in causing mortality against first to sixth instar eggs and neonate larvae seven days post-treatment, and their effects on the feeding performance of sixth instar larvae at 48 h post-treatment at three concentrations (1 × 10 , 1 × 10 , and 1 × 10 conidia mL ) were also assessed. The six instar larvae were not susceptible to the five tested fungal isolates. However, ZK-5 caused the highest egg mortality of 40, 70, and 85.6% at 1 × 10 , 1 × 10 , and 1 × 10 conidia mL , respectively, followed by CTD-24 (30.6, 50, and 75.6%) and SE-10 (25.6, 40, and 55.6%). In addition, ZK-5 caused the highest neonate mortality of 54.3% at 1 × 10 conidia mL . ZK-5 and CTD-24 caused cumulative mortality, including 93.3 and 83.3% mortality of eggs and neonates, respectively, at 1 × 10 conidia mL . Furthermore, ZK-5 reduced the feeding efficacy of first to third instar larvae by 66.7 to 78.6%, while CTD-24 and SE-10 reduced larval feeding by 48.3 to 57.1% at 1 × 10 conidia mL . However, these fungal isolates were less potent in reducing the feeding activity of fourth to sixth instar larvae (>46% with at 48 h post-treatment). The tested fungal isolates could play an essential role as microbial biopesticides in suppressing the population in China after further investigations on their efficacy are obtained in the field.