Pesticides are good at killing pests, but they also massacre a lot of other things. In recent years conservation has come forward as an idea to control pests naturally. The idea is relatively straightforward. Crops are an all-you-can-eat buffet for pests. The pests should be an all-you-can-eat buffet for predators, but often they need more from an environment than food. Keeping non-crop habitats close to crops gives them somewhere to shelter, and keeps them close when they forage for food. As a result, conservation should be a win-win strategy. Nature avoids being slaughtered by pesticides, and farmers save money on defending their crops.
A new study published in PNAS by Daniel Karp and 135 colleagues says this is often the case. But not always. The problem was that local geography played a significant role in whether or not conservation worked as pest control.
Writing in PNAS, Karp and colleagues say: “By compiling and systematically analyzing the largest pest-control database of its kind to date, we have demonstrated that landscape composition alone can explain variation in the abundance and activity of natural enemies and crop pests. Critically, however, we found remarkable variability in how pests and enemies respond to different landscape metrics, preventing the prediction of pest-control responses by simple empirical models constructed from independent datasets. Ultimately, these results suggest that natural habitat conservation cannot be considered a panacea.”
In some cases, they found that pests also benefitted from increased shelter around the crops.
The authors also found that models of pest abundance were better at predicting reality for some parts of the world than others. They note: “[E]xplanatory power varied geographically. For example, models from Nearctic and Palearctic realms generally explained more variation in pest abundance and activity than models from other areas. This difference may result from latitudinal variation in data quality. Fewer regional land-use maps exist in data-poor tropical areas, and informal inspection of the global land-use map suggested that land-cover classifications were often inaccurate in tropical landscapes.”
They conclude that conservation-based approaches to crop control need close attention to the local landscape that they are being applied in. As well as making sure farmers are getting the benefits they’re looking for, the recording of data can increase the accuracy of the models and make them more useful elsewhere.
Karp, D. S., Chaplin-Kramer, R., Meehan, T. D., Martin, E. A., DeClerck, F., Grab, H., … Martínez-Salinas, A. (2018). Crop pests and predators exhibit inconsistent responses to surrounding landscape composition. Proceedings of the National Academy of Sciences, 201800042. https://doi.org/10.1073/pnas.1800042115