The push–pull intercrop Desmodium does not repel, but intercepts and kills pests
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Curated by eLife
eLife assessment
This valuable study addresses both commonly accepted and alternative hypotheses for the mechanism by which an intercrop supports pest control in push-pull agriculture, a promising and broadly recognized approach for sustainable intensification. The findings address a widely recognized gap in data on the mechanism underlying push-pull systems and thus can be important for work on pest control in agroecology as well as plant-herbivore interactions more generally. The support of claims is solid, combining observations of several different mechanistic aspects in an uncommonly broad range of relevant environments with clear reasoning regarding experimental design, but also using some non-standard approaches that are not as well explained, complicating comparisons to the current state of the art.
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Abstract
Over two decades ago, an intercropping strategy was developed that received critical acclaim for synergizing food security with ecosystem resilience in smallholder farming. The push–pull strategy reportedly suppresses lepidopteran pests in maize through a combination of a repellent intercrop (push), commonly Desmodium spp., and an attractive, border crop (pull). Key in the system is the intercrop’s constitutive release of volatile terpenoids that repel herbivores. However, the earlier described volatile terpenoids were not detectable in the headspace of Desmodium , and only minimally upon herbivory. This was independent of soil type, microbiome composition, and whether collections were made in the laboratory or in the field. Furthermore, in oviposition choice tests in a wind tunnel, maize with or without an odor background of Desmodium was equally attractive for the invasive pest Spodoptera frugiperda . In search of an alternative mechanism, we found that neonate larvae strongly preferred Desmodium over maize. However, their development stagnated and no larva survived. In addition, older larvae were frequently seen impaled and immobilized by the dense network of silica-fortified, non-glandular trichomes. Thus, our data suggest that Desmodium may act through intercepting and decimating dispersing larval offspring rather than adult deterrence. As a hallmark of sustainable pest control, maize –Desmodium push–pull intercropping has inspired countless efforts to emulate stimulo-deterrent diversion in other cropping systems. However, detailed knowledge of the actual mechanisms is required to rationally improve the strategy, and translate the concept to other cropping systems.
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eLife assessment
This valuable study addresses both commonly accepted and alternative hypotheses for the mechanism by which an intercrop supports pest control in push-pull agriculture, a promising and broadly recognized approach for sustainable intensification. The findings address a widely recognized gap in data on the mechanism underlying push-pull systems and thus can be important for work on pest control in agroecology as well as plant-herbivore interactions more generally. The support of claims is solid, combining observations of several different mechanistic aspects in an uncommonly broad range of relevant environments with clear reasoning regarding experimental design, but also using some non-standard approaches that are not as well explained, complicating comparisons to the current state of the art.
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Reviewer #2 (Public Review):
This MS reveals that plants that have long been said to push are not, in fact, doing so, but are trapping and killing pests, thereby reducing pest outbreaks. The volatiles data of Desmodium are stable and useful. And the method of showing volatiles data is great.
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Reviewer #3 (Public Review):
This study succeeds to highlight and address important gaps in our understanding of plant-insect interactions mediating pest control in a widely known agro-ecological system for sustainable intensification, push-pull agriculture. In particular, the authors present a large amount of data on plant volatile emission, thought to be critical for the functioning of these systems, in reasonable and relevant contexts, as well as on other traits of the plants in the system relevant for pest control. These data come from plants grown both in controlled and field environments, which is unusual. The arguments on mechanism are further supported by insect behavioral assays, which seem to be thoughtfully designed, but also use some non-standard approaches that could be better explained. While most or all of the authors' …
Reviewer #3 (Public Review):
This study succeeds to highlight and address important gaps in our understanding of plant-insect interactions mediating pest control in a widely known agro-ecological system for sustainable intensification, push-pull agriculture. In particular, the authors present a large amount of data on plant volatile emission, thought to be critical for the functioning of these systems, in reasonable and relevant contexts, as well as on other traits of the plants in the system relevant for pest control. These data come from plants grown both in controlled and field environments, which is unusual. The arguments on mechanism are further supported by insect behavioral assays, which seem to be thoughtfully designed, but also use some non-standard approaches that could be better explained. While most or all of the authors' results pre-date some relevant recent publications in this field, they do incorporate comparisons to current literature in order to better place their findings in the current state of the art.
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