Exploring the dismantlement of indigenous pest management in the Andes

Andean potato weevils (Premnotrypes spp.) are considered the most serious pest of potatoes in the Andean region, where they are native. Some traditional farming systems are known to maintain their populations bellow damage levels, but the mechanisms behind this suppression remain poorly understood. Relying on participatory observations, extensive interviews with farmers, archival reviews and GIS technology, I characterized a regional “natural experiment” where the intensification of a traditional farming system across 16 farming communities in Bolivia was followed by aggressive upsurges of Andean potato weevils. The response of weevils to intensification appeared to be best explained by the loss of cultural controls inherent to the traditional farming system, which created physical barriers to weevil dispersal into potato fields (i.e. improved connectivity hypothesis). By transferring potato fields to a distant location each year, the traditional system putatively isolated foraging weevils, which can only disperse by walking, through the combined influence of distance (mean=1.27 Km), and natural streams (mean=1.2 streams). A subsequent observational study of 4 farming communities in Peru tested this hypothesis with a random sample of 140 farmer’s fields. A statistical model explaining weevil infestations in these fields supported the improved connectivity hypothesis. In addition, the model predicted weevils also respond negatively to the spatial aggregation of potato fields, another key feature of the traditional farming systems in the central Andes. These results highlight the importance of landscape structure in the sustainable management of Andean potato weevils.