Evaluation of key parameters for developing a Metarhizium rileyi‐based biopesticide against Spodoptera frugiperda (Lepidoptera: Noctuidae) in maize: laboratory, greenhouse, and field trials

Abstract

BACKGROUND: The entomopathogenic fungus Metarhizium rileyi is known to cause natural infections in some caterpillars. In this multiyear study, we carried out laboratory, greenhouse and three field trials with the aim of developing a sustainable option for control of the fall armyworm (FAW) in maize. Association of M. rileyi with Spodoptera frugiperda baculovirus (SfMNPV) and delivery strategies were also investigated. RESULTS: The selected isolate (CG381) was effective in the laboratory at a low concentration (~4 × 10 3 conidia cm −2 ), killing >95% of FAW larvae within 8 days. In the greenhouse assay, applications of conidia suspended in water or as dry powder in maize whorls (~6.3 × 10 6 conidia per plant) produced similar larval mortalities (88%-96%). In the field trials, conventional spraying of unformulated conidia (0.6 and 1.2 × 10 12 conidia ha −1 ) caused low larval mortalities (27-31%). Simultaneous application of either unformulated or oil-based formulations of M. rileyi conidia and S. frugiperda baculovirus (SfMNPV) to plant rows caused larval mortalities comparable with each of the pathogens applied alone. However, when a formulation containing both pathogens was sprayed directly into the whorls, the overall mortality of S. frugiperda larvae due to pathogens (mostly to M. rileyi infections) reached ~59%, twofold higher than the other treatments with conventional spraying, whereas in the control, the overall mortality was only 1%. CONCLUSION: Optimizing exposure of S. frugiperda larvae to an inoculum of virulent entomopathogens through directed applications to maize whorls is critical to produce satisfactory mortality levels and is promising for integrated pest management.

Pathogenicity of Beauveria bassiana PfBb and Immune Responses of a Non-Target Host, Spodoptera frugiperda (Lepidoptera: Noctuidae)

“…Alternatively, a large number of studies have shown that B. bassiana is pathogenic to S. frugiperda [ 35 , 36 ], and that B. bassiana could be compatible with natural enemies to improve the control effect [ 37 ]. Therefore, entomopathogenic fungi could be prime substitutes for insecticides [ 38 , 39 ]. However, most entomopathogenic isolates show high mortality only to young larvae but low pathogenicity to old larvae [ 40 ].…”

Potential Impact of Chemical Fungicides on the Efficacy of Metarhizium rileyi and the Occurrence of Pandora gammae on Caterpillars in Soybean Crops

“…The OD formulation had some advantages, such as increasing the rate of the infection process and reducing the time to kill the host (lower ST 50 ), despite no significant difference in the reduction in survival time relative to that observed for unformulated conidia. The advantages of oil-based formulations in enhancing the infectivity of the selected strains of M. rileyi [9,19,20,23] and reducing damage to plants [22] have been reported in other studies. Emulsifiable oils facilitate biopesticide manipulation by the end user as an alternative to formulate highly hydrophobic dry conidia of M. rileyi.…”

“…Simple formulations may protect conidia from abiotic stressors, as previously reported for species in the Metarhizium anisopliae complex [15][16][17], including the negative effects of some chemical fungicides [18]. For the fungus M. rileyi, only experimental low-cost formulations have been tested under laboratory conditions [19][20][21], greenhouse [22], and field conditions [9,23]. However, information on how these formulations may protect M. rileyi conidia from the negative effects of the chemical fungicides used in soybean crops is unavailable.…”

Identification of entomopathogenic fungus Metarhizium rileyi infested in fall armyworm in the cornfield of Korea, and evaluation of its virulence

“…The virulence of M. rileyi depends on the host insect species, developmental stage, fungal strain, spore concentration, and experimental conditions (Dutta et al, 2014; Faria et al, 2022; Montecalvo et al, 2022; Shylesha et al, 2018; Zhou et al, 2020). Bosa et al (2004) evaluated the susceptibility of FAW to 10 strains of M. rileyi , finding that the mortality ranged from 73% to 100%.…”

“…The virulence of M. rileyi was evaluated as described by Faria et al (2022) with some modifications. Fourth‐instar larvae of FAW ( n = 6/replication) were inoculated by spraying with M. rileyi conidial suspension (1 × 10 7 /ml) prepared in distilled water with a surfactant (Tween‐80, 0.05% v/v).…”