SPATIAL AND TEMPORAL CONTEXT-DEPENDENCE IN THE PUSH-PULL SYSTEM
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Ecological intensification is a set of practices and principles aimed at managing biodiversity to maintain or enhance crop yields while reducing negative environmental impacts of conventional agriculture. One of the most successful examples of ecological intensification is the push-pull system developed by the International Centre of Insect Physiology and Ecology (ICIPE) for cereal crops in Africa. First developed in the 1990s, the push-pull system utilizes two companion crops alongside a cereal grain (most often maize) to reduce pressure from insect pests and parasitic weeds, enhance soil quality, and dramatically improve yield. While the push-pull system provides significant benefits to growers, its impacts also vary for reasons that are not well-understood. Working closely with our collaborators at ICIPE, SLU, and Lund University, we examined different drivers that could influence the effectiveness of the push-pull system. We found that push-pull fields which had been established for longer had stronger pest suppression and higher yield. Interestingly, the pest suppression benefits showed some evidence of spilling over to neighboring control fields, meaning that the longer a push-pull field was established, the lower the pressure on its neighboring control field as well. We also found that push-pull was resilient across weather and landscape gradients. While push-pull’s effect was slightly weaker in certain conditions (including in landscapes with a high percentage of surrounding agriculture), push-pull fields always outperformed control fields by significant margins. Finally, we found that biological control services in push-pull fields could vary with both time within the growing season and surrounding landscape context. Early in the growing season push-pull fields had higher levels of pest egg predation than control fields, but later in the season this pattern reversed on farms surrounded by more natural area. Overall, we find that even where push-pulls benefits may vary, they are robust across time, landscape context, and weather context, and are likely to remain so in the future. More broadly, we consider our results encouraging for ecological intensification in general, showing that ecologically intensified systems may be robust over extended timespans, across a range of environmental conditions, and against novel invasive pests.
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Van Nouhuys, Saskya