Agricultural intensification is thought to disrupt the ability of ecosystems to provide pest control services, but the mechanisms remain poorly characterized. This research characterizes the response of Andean potato weevils ( Premnotrypes spp.) to the intensification of potato agriculture in the Andes. I present a case study where Andean potato weevils became pests across 16 adjacent farming communities in Bolivia only after farmers abandoned their traditional rotation system, known as the sectoral fallow system. My observations led me to hypothesize that weevil populations responded positively to changes to the agricultural landscape that brought foraging individuals in closer and uninterrupted proximity to potato fields (i.e. improved connectivity hypothesis). By transferring potato fields to a distant location each year, the sectoral fallow system appeared to isolate foraging weevils, which can only disperse by walking, through the combined influence of distance and natural streams. In a subsequent study of 4 farming communities in the Peruvian Andes, I tested the improved connectivity hypothesis with a random sample of 140 potato fields. Quantitative evidence supported this hypothesis. In addition, the study revealed that weevils responded negatively to the aggregation of potato fields. This led to the inference that sectoral fallow systems also suppressed weevils by demanding farmers to aggregate their potato fields in only one sector of the collectively-managed farmscape each year. Finally, through a series of statistical models predicting weevil infestations in 138 of the previously-mentioned fields, I found that predictors estimating weevil isolation and potato aggregation in the area neighboring a focal field were substantially more important than predictors characterizing the field’s ecology and management. The latter predictors included the number insecticide treatments, the choice of potato cultivar and 27 others that Andean agronomists considered important. These results highlight the importance of landscape structure in explaining the abundance of Andean potato weevils. This research is one of very few studies fully characterizing a change in pest status in response to agricultural intensification, and one of the first to link the status change to changes in landscape structure.
|Advisor:||Rosenheim, Jay A.|
|Commitee:||Karban, Richard, Zalom, Frank G.|
|School:||University of California, Davis|
|School Location:||United States -- California|
|Source:||DAI-B 71/03, Dissertation Abstracts International|
|Keywords:||Agricultural intensification, Andean agriculture, Andean potato weevil, Ecosystem services, Indigenous knowledge, Pest management, Premnotrypes|
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