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Horizontal transmission of Paranosema locustae (Microsporidia) in grasshopper populations via predatory natural enemies.

BACKGROUND
Paranosema locustae Canning, 1953 (Microsporidia) provides effective control of grasshoppers. Horizontal transmission of P. locustae is known to occur, and evidence for the mechanism of this transmission via predatory natural enemies has been found. We conducted a 3-year laboratory and field study to assess the potential impact of feces from both grasshoppers Locusta migratoria L. and their natural enemies on the persistence of P. locustae.


RESULTS
We found that P. locustae persisted among grasshopper populations in treated areas and in adjacent untreated areas for up to 2 years, and the density of grasshoppers decreased in both areas. We showed that healthy grasshoppers could be infected by eating food contaminated by feces from their natural enemies. Grasshopper predators retained a large number of spores acquired from eating grasshoppers infected with P. locustae. Spores in the feces of the main natural enemy, the beetle Pterostichus gebleri Dejean 1828, in the treated area showed clear viability.


CONCLUSION
These results demonstrate that predatory natural enemies are important vectors for this microsporidian disease, and suggest that sustainable transmission and continuing population suppression might be achieved by horizontal transmission via natural enemies, which should be maximized to increase the effectiveness of P. locustae. © 2018 Society of Chemical Industry.