Long-term patterns of occurrence of Nosema locustae and Perezia dichroplusae (Microsporidia) in grasshoppers (Orthoptera: Acrididae) of the Pampas, Argentina

The long-term (through the years) occurrence of the two known microsporidia parasitizing grasshoppers of the subfamily Melanoplinae in the Pampas of Argentina (vertically transmitted, native Perezia dichroplusae and horizontally transmitted, introduced Nosema locustae) was monitored at 13 localities from 1995 to 2003. Nosema locustae occurred at nine localities, and R dichroplusae at five. There was almost no overlap of occurrence, and mixed infections Were not registered. The presence and prevalences (1% to 6.1%) of R dichroplusae were relatively stable over the years in all localities while N. locustae alternated years of presence and absence, and prevalences fluctuated markedly from 1.8% up to 41%. On four instances, each at a different locality, unusually high prevalences (epizootics) of N. locustae were recorded. Natural epizootics of such magnitudes are not known for N. locustae in other regions of the world.