Analysis of the 2015–2025 upsurges of the South American Locust, Schistocerca cancellata: Evidence of a regional migratory circuit between Argentina and Paraguay/Bolivia

After an absence of almost 60 years, a major upsurge of the South American locust, Schistocerca cancellata , occurred in Argentina and neighboring countries from 2015 to 2020, with a further upsurge during 2024 and 2025. We analyzed locust occurrence records from Argentina, Paraguay, and Bolivia, together with temperature and rainfall data, to examine the sequence of breeding and migration during these periods. The results show repeated alternation of locust activity between Argentina and Paraguay/Bolivia, consistent with a regional migratory circuit. Detailed seasonal analyses indicate that upsurges were sustained by several generations of breeding within seasons, including asynchronous or multi-cohort development under variable rainfall conditions. While historical outbreaks originated mainly in traditional outbreak areas, specifically in the provinces of Catamarca and La Rioja in northwest Argentina, breeding now occurs over a much larger area extending from the traditional outbreak areas northwards into Paraguay and Bolivia and is likely associated with extensive clearing of the forests of the Grand Chaco. These findings indicate that the population dynamics of S. cancellata have changed, with implications for monitoring and control strategies, which must now operate on a broader regional scale.