Virulence of Beauveria sp. and Metarhizium sp. fungi towards Fall armyworm (Spodoptera frugiperda)

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Abstract
Since 2016, the fall armyworm (Spodoptera frugiperda, J.E. Smith) has spread from the Americas to invade many regions of the world, including Australia in early 2020. The development of effective pest management strategies for S. frugiperda is a high priority for crop protection. In the invasive range, the degree to which endemic biological control agents can constrain S. frugiperda remains sparsely investigated. This study examines 11 isolates of fungi including six Beauveria isolates and five Metarhizium isolates from Oceania for their potential as S. frugiperda biocontrol. Two Beauveria isolates (B-0571, B-1311) exhibited high virulence toward S. frugiperda caterpillars and adults. The overall mortalities over seven days in 3rd and 6th instar caterpillars and moths (respectively) for B-0571 was 82.81 ± 5.75, 61.46 ± 6.83, and 93.75 ± 3.61, and for B-1311 was 73.72 ± 2.51, 71.88 ± 5.41, and 97.92 ± 2.08%. The majority of deaths in the caterpillars occurred within the first 24 hours (3rd instar control 0.74 ± 0.33%, B-0571 73.96 ± 7.85 and B-1311 62.08 ± 3.67%; 6th instar control 0%, B-0571 66.67 ± 11.02% and B-1311 62.5 ± 9.55%). Infection from both isolates fully prevented reproduction in surviving S. frugiperda females. The two isolates, however, cause a significantly lower mortality in a native noctuidae species: Helicoverpa armigera (3rd instar B-0571 44.79 ± 4.54% and B-1311 19.80 ± 7.51%). The discovery of two fungal isolates with high virulence to S. frugiperda caterpillars and adults opens new avenues for the development of biological control tools for this invasive moth pest. Such tools may also provide additional options for control of native pest lepidoptera, and reduce selection pressure for resistance to Bt and synthetic insecticides.

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