Virulence of the fungal pathogen, Aspergillus oryzae XJ-1 in adult locusts (Orthoptera: Acrididae) in both laboratory and field trials.

Abstract

Locusts and grasshoppers are pests of many agricultural crops, and their frequent outbreaks worldwide threaten food security. Microbial control agents are currently used to suppress the early (nymphal) stages of pests, but they are often less effective against adults, which are primarily responsible for locust plagues. The fungal pathogen Aspergillus oryzae XJ-1 has high pathogenicity in locust nymphs. To assess its potential for controlling locust adults, we evaluated the virulence of A. oryzae XJ-1 (i.e., locust Aspergillus, LAsp) in locust adults using laboratory, field-cage experiments, and a field trial. The lethal concentration of LAsp in adult Locusta migratoria was 3.58±0.09×105 conidia/ml 15 days after inoculation in the laboratory. A field-cage experiment showed that the mortalities of adult L. migratoria were 92.0±4.6% and 90.1±3.2% 15 days after inoculation with 3×105 and 3×103 conidia/m2 of LAsp, respectively. A large-scale field trial of 666.6 ha was conducted, in which a LAsp water suspension was applied at a concentration of 2×108 conidia/ml in 15 L/ha by aerial spraying via drones. The densities of mixed populations of L. migratoria and Epacromius spp. were significantly reduced by 85.4±7.9%-94.9±5.1%. In addition, the infection rates of surviving locusts collected from the treated plots were 79.6% and 78.3% on the 17th and 31st day after treatment, respectively. These results indicate that A. oryzae XJ-1 is highly virulent in adult locusts and that it has high potential for the control of locusts.