Native Herbivore Becomes Key Pest After Dismantlement of a Traditional Farming System

Abstract

Agricultural intensification is thought to disrupt the ability of ecosystems to provide pest control services. The mechanisms often held responsible are a reduction in natural enemies (natural enemies hypothesis), an increase in the scale of cultivation (resource concentration hypothesis), and a relaxation of host plant defenses (defense relaxation hypothesis). In addition, climate change could be a hidden cause behind modern pest population changes. Relying on participatory observations, extensive interviews with farmers, archival reviews, and GIS technology, I document a regional “natural experiment” where agricultural intensification across 16 traditional farming communities in Bolivia was followed by aggressive attacks of an endemic potato herbivore, the Andean potato weevil ( Premnotrypes spp.). I characterize the specific changes involved and speculate on their potential contributions to weevil upsurges within the context of the resource concentration, natural enemies, defense relaxation, and climate change hypotheses. The evidence presented points to an additional explanation for this abrupt shift in pest status: agricultural intensification dismantled cultural controls inherent to the traditional farming system that inhibited weevil dispersal into potato fields. Based on this evidence, I submit the improved connectivity hypothesis as an additional explanation for Andean potato weevil upsurges in the study region.