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Crop production depends partly on interactions among plants, herbivores, and natural enemies. A 2026 synthesis published in Science Advances examined these relationships using 149 field studies spanning 27 countries and five continents. The researchers asked how increasing plant species richness relates to organisms across three trophic levels, and whether these relationships differ among ecosystems.
The three trophic levels examined were plants, the invertebrate herbivores that feed on them, and the invertebrate natural enemies that prey on or parasitize those herbivores. Changes in one trophic group can affect the others. By comparing croplands, grasslands, and forests, the study examined whether higher plant diversity was associated with patterns consistent with top-down control or bottom-up effects. The cropland findings support evaluating diversification as part of pest management, rather than assuming that adding plant species will always suppress pests.
The synthesis combined 149 field studies that differed in species composition, climate, and methods. It included organic and nonorganic croplands, grasslands, and forests, allowing the authors to compare responses across ecosystems and climatic regions. The dataset combined experiments that manipulated plant species richness with observational studies of existing diversity differences.
The authors compared lower with higher plant species richness. They examined gradients of plant richness and tracked what happened to each trophic level as diversity rose. These analyses tested whether the observed relationships were consistent with proposed trophic pathways. However, the synthesis did not directly demonstrate the causal mechanisms underlying those relationships.
Figure 1. Geographic distribution of the studies, plant species richness, and sampling coverage across ecosystems and climatic regions. (Wan, et al., 2026)
In croplands, the results were consistent with stronger top-down control. Higher plant diversity was associated with improved natural enemy performance and reduced herbivore performance. Natural enemies included both predators and parasitoids. Their performance was assessed using measures such as abundance, diversity, predation, and parasitism, while herbivore performance included abundance, feeding damage, and diversity. These combined measures should not be interpreted as organism counts alone.
Top-down pest control occurs when natural enemies suppress herbivores. The authors discuss habitat complexity, alternative food resources, and chemical cues as possible explanations for the benefits of plant diversity to natural enemies. They also consider whether concentrated host resources in monocultures favor specialist herbivores. The synthesis did not establish which mechanism explained the response in every crop system or compare the costs and effectiveness of diversification with insecticides. For researchers considering biological approaches, biocontrol products represent a related area to explore, with suitability assessed for the target pest and experimental conditions.
Grasslands and forests showed patterns more consistent with bottom-up effects, in which plant resources support herbivores and, in turn, their natural enemies. This does not mean that plants necessarily become more resistant to herbivores. Greater resource availability can also support increased herbivore performance. In the comparison between lower and higher plant diversity, the increase in combined plant performance was statistically significant in grasslands, but not in either cropland category or forests.
Resource complementarity among plant species is one explanation discussed by the authors for increased plant productivity. However, the study did not show that bottom-up and top-down pathways universally reinforce each other within the same system. Plant performance included growth, reproduction, and quality, rather than a general measure of tolerance to attack. Services such as plant traits identification can support the characterization of plant material for follow-up research, but determining which traits influence trophic responses requires additional experiments.
The team applied piecewise structural equation modeling to examine direct and indirect statistical relationships among plant diversity and the performance of the three trophic groups. Cropland patterns were consistent with top-down effects, whereas grassland and forest patterns were more consistent with bottom-up effects. The models did not show that both pathways strengthened together in every ecosystem, and not every individual relationship was statistically significant.
The authors explicitly caution that these patterns represent correlations rather than conclusive evidence of causal trophic cascades. Experiments combining plant diversity manipulations with direct measurements of predation, parasitism, and herbivory would help test the proposed mechanisms. The analysis also did not establish greater temporal stability of the entire community. Separately, plant resistance identification may help evaluate cultivar responses to herbivores in follow-up studies; resistance should not be treated as equivalent to bottom-up resource effects.
The cropland findings support evaluating diversification within integrated pest management. They do not establish an optimal planting mixture, a year-round habitat prescription, or a guaranteed reduction in chemical inputs. Existing management also matters: the cropland studies used pest-suppression practices, and these practices were applied consistently within each study's comparison of plant diversity treatments.
Managers can act at several scales. However, this synthesis did not determine which combination of field and landscape interventions works best. Intercropping is relevant to plant species richness, while mixtures of cultivars within a single species represent a different form of diversity. Follow-up work involving plant breeding could evaluate cultivar performance in selected planting systems, while analytical services could support measurements chosen for the experimental design. These are potential research applications, rather than outcomes demonstrated by the synthesis.
The study's cross-ecosystem scope—cropland, grassland, and forest—allowed the authors to identify differences in trophic responses. Its results should not be interpreted as evidence that plant diversity produces the same pest-control benefits in every ecosystem. Pollination, soil health, and carbon retention were not the response variables used to establish the reported trophic patterns.
For crop research, a useful next step is to measure plant performance, herbivore abundance and damage, and natural enemy responses together under defined management conditions. Depending on the project, plant physiology analysis and high-throughput phenotyping may support the plant measurements. This is a proposed application of the findings, rather than a protocol validated by the synthesis. Reductions in insecticide use, fertilizer requirements, or production costs would need to be measured directly before being claimed.
Across 149 field studies, plant diversity was associated with different trophic responses in croplands, grasslands, and forests. Cropland results were consistent with stronger top-down control, while grasslands and forests showed patterns more consistent with bottom-up effects. The findings support further tests of diversification within crop pest management, while emphasizing the importance of ecosystem type, existing management practices, and the distinction between statistical associations and demonstrated mechanisms.
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