Print PageSecondary pest outbreaks occur when the use of a pesticide to reduce densities of an unwanted target pest species triggers subsequent outbreaks of other pest species. Although secondary pest outbreaks are thought to be familiar in agriculture, their rigorous documentation is made difficult by the challenges of performing randomized experiments at suitable scales. Here, we use an ecoinformatics approach to quantify the frequency and monetary cost of secondary pest outbreaks elicited by broad-spectrum insecticides to control the plant bug Lygus hesperus in cotton. We gathered data that detail pest-control practices for cotton grown in California's San Joaquin Valley, USA. Our analysis uses innovative statistical methods that define causal effects via potential outcomes, and that provide formal methods to estimate causal effects from non-experimental data. This talk will combine a discussion of the secondary pest outbreaks triggered by early-season insecticide treatment for Lygus with an introduction to the theory underlying causal inference statistics.
Results/Conclusions
We find that, in fields that received an early-season, broad-spectrum insecticide treatment for Lygus, 20% (s.e. 4%) of late-season pesticide costs were attributable to secondary pest outbreaks elicited by early-season insecticide application for Lygus. Individual herbivore species responded in rough proportion to their overall occurrence as late-season pests. In 2010 US dollars, secondary pest outbreaks cost farmers an additional US$6.0 (s.e. US$1.3) per acre in management costs. To the extent that secondary pest outbreaks may be driven by eliminating pests' natural enemies, these figures place a lower bound on the monetary value of ecosystem services provided by native communities of arthropod predators and parasitoids in this agricultural system. Our analysis also demonstrates statistical methods that can be used to draw rigorous inferences about causality from data collected outside an experimental framework.
