Many studies have considered the relationship between landscape-scale habitat complexity and ecosystem services provided to agriculture, but trends with respect to pest control are not readily apparent. Here we conduct a formal meta-analysis of 41 studies investigating the effect of landscape complexity on insects in agricultural systems in order to elucidate general patterns in the response of pest control to habitat surrounding the farm. Of these, 34 studies examined natural enemy response and 17 examined herbivore response for a total of 151 responses. Through this meta-analysis, we explored the effects of different metrics of landscape complexity on insect abundance, diversity, and predation or parasitism, and how these responses vary for specialists and generalists and at different scales.
Results/Conclusions
Natural enemies show a clearly significant response to landscape. There is a larger effect of landscape complexity on natural enemy diversity and predation or parasitism than on enemy abundance or herbivore diversity, and the effect on herbivore abundance is not significant. Generalist enemies have a stronger response to landscape complexity than specialists, but this pattern is reversed for herbivores. Larger scales appear to be associated with stronger natural enemy response, though this depends on how landscape complexity was defined and the methods used to characterize it. Despite positive effects on natural enemies, consistent suppression of pests has not been detected in complex landscapes, at least over the short timescales of these ecological studies. Nevertheless, landscape complexity rarely exacerbates pest problems. Future studies should be explicit in their measurement of landscape complexity and include both natural enemies and herbivores to better address the question of landscape's effect on pest control.
