Plant chemical diversity and its frequency have distinct but complementary effects on insect foraging

Variability in plant traits such as nutrients and defences can challenge insect herbivores searching for a host plant. Cultivar mixtures are designed to harness this variability to reduce herbivore damage in agroecosystems but have had mixed success. We examine how the spatial frequency of plant trait variability-a fundamental but rarely examined feature of variability-influences insect foraging and survival. We released a generalist herbivore into monocultures of two chemically distinct tomato varieties or dicultures of the two varieties with two spatial frequencies of chemical diversity and tracked herbivore movement and feeding damage. We found the pattern of herbivore feeding damage was more spatially concentrated in both diculture treatments than in either monoculture, indicating that the presence of chemical diversity, regardless of its spatial frequency, influences herbivore foraging. In contrast, total amount of feeding damage was reduced by 25% in dicultures where genotypes were grouped compared to monocultures or dicultures with alternating genotypes, which had similar levels of damage. Similarly, herbivore survival in the low-frequency diculture was nearly half the survival in the high-frequency diculture or monocultures. Synthesis and applications. Whereas previous work investigates how the amount of chemical diversity in a plant population influences insect ecology, our results indicate that local spatial distribution of diversity is equally important. A key implication of this work is the potential to design cultivar mixtures spatially, at the movement scale of target organisms, to create more effective pest management landscapes and promote sustainable agriculture.

Automated summary

The variability in plant traits affects insect herbivores' foraging and survival. The presence of chemical diversity influences herbivore foraging behavior, while grouped cultivar mixtures reduce feeding damage and improve herbivore survival. The findings suggest the potential to spatially design cultivar mixtures at the movement scale of target organisms to promote sustainable agriculture.