Pest variability is poorly understood – California Agriculture News Today

Daniel Paredes, UC Davis ecologist: Understanding Pest Variability Key to Managing Pest Outbreaks

Recently published research led by UC Davis ecologist Daniel Paredes suggests that pest abundance is less variable in diverse landscapes composed of multiple crop types and patches of natural habitat.

“As a result, pest outbreaks are less likely in diverse landscapes,” said Paredes, who analyzed a 13-year-old government database of diverse landscapes encompassing more than 1,300 olive groves and vineyards in Spain. The database documented pests and pesticide applications.

The article, “The causes and consequences of pest population variability in agricultural landscapes,” appears in the journal Ecological Society of America, Ecological applications. Co-authors are Jay Rosenheim, UC Davis Distinguished Professor of the Department of Entomology and Nematology, and Daniel Karp, Associate Professor, Department of Wildlife, Fish, and Conservation Biology. The research is online at

Variability of pests: an understudied but critical subject
Although population variability is often studied in natural systems, the need for long-term data on pest populations collected from many farms has largely prevented researchers from studying pest variability in agricultural systems, said Paredes, postdoctoral fellow at the Karp laboratory.

“However, understanding the variability of agriculture is key to understanding when pest outbreaks are likely to occur,” Paredes said. “Farmers are really risk averse, with the fear of very rare but serious pest outbreaks driving their decisions. But huge data sets are needed to understand when outbreaks are likely to occur and better inform management.

“We found that more variable pest populations are more likely to degrade crop quality and induce catastrophic damage,” Paredes said. “For example, the likelihood of olive flies consuming more than 20 percent of olive crops doubled when comparing the most volatile populations to the least volatile populations.”

What makes a pest population variable?
After showing that greater variability in pest populations is more likely to cause problems for farmers, the researchers then set out to find out what farmers could do to manage the variability.

A key factor that emerged was the type of landscape in which crops were grown, particularly whether the landscape was dominated by large fields of a single or more diverse crop variety. Pest populations were both more abundant and more variable in monocultures.

However, while landscape type influenced both the size and variability of pest populations, this was not always the case for other variables. “This research shows that the factors that promote high overall average pest density are not necessarily the same factors that promote high variability in pest density,” Rosenheim said. “So average densities, which researchers have been studying for decades and decades, are only part of the story. Variations in density, and especially unpredictable severe outbreaks, must be studied separately.

The take home message?

“In Spain, planting multiple crops and maintaining natural habitats would help suppress pests stably and prevent epidemics,” said Paredes, a native of Spain and holder of a PhD in environmental science (2014). from the University of Granada. “Diversifying agriculture can be a win-win situation for conservation and farmers.”

“Therefore, we encourage agricultural actors to increase the complexity of the landscapes surrounding their farms by conserving/restoring natural habitat and/or diversifying crops,” the researchers write in their abstract.

Harnessing other large datasets like this will be key to understanding whether diverse landscapes also help mitigate pest variability and outbreaks in other regions, they said.

This project was funded by the National Science Foundation with funds from the Belmont Forum via the European Biodiversity Partnership: BiodivERsA. It was also supported by the USDA’s National Institute of Food and Agriculture.