Environmental factors associated to breeding areas of the South American locust Schistocerca cancellata on a regional scale

Abstract

Locusts are globally recognized as major pest threats. In the first half of the 20th century, the South American locust caused great economic losses. After the implementation of preventive management, large-scale upsurges ceased. In 2015, resurgence of S. cancellata led to swarms affecting northern Argentina, Paraguay, and Bolivia, prompting control agencies to address an almost forgotten problem. After six decades without a major locust outbreak, there were limited and outdated studies on this species. This study aims to identify key environmental factors associated with the spatial distribution of S. cancellata oviposition sites. We focus on explanatory variables that represent physical and chemical properties of soil and vegetation cover. To understand the relationships between each potential explanatory variable and the presence-absence of S. cancellata oviposition sites, we first performed regression analyses applying a linear and quadratic structure for each explanatory variable. Then, we performed comparisons of logistic regression models in a multi-model inference framework, where CAIC and weights of evidence were analysed. Our results show that the South American locusts chose to lay their eggs in areas with a low proportion of natural forest and flooded grasslands and a high proportion of non-vegetated areas, where the soils are flat, with neutral pH, and low salinity. We also determined that an increase in the proportion of cultivated areas is associated with an increase in the probability of breeding presence of this species. The locust's habitat falls within the Dry Chaco, a global deforestation hotspot, evidencing a rapid replacing of forests for plantations. Since both the diminish of forest and the increase in cultivated areas are associated with an increase in oviposition sites, we consider that breeding areas will likely increase. The results found herein can be used to map the potential breeding habitats to help preventive management against the South American locust.