Background/Question/Methods
Plant genetic diversity often has important effects on arthropod communities. However, the mechanisms behind these effects are poorly understood because little research has linked genetic diversity with phenotypic diversity. Manipulations of plant chemical traits are lacking because plants vary in many traits and identifying the specific chemical functional trait has been difficult. Our objective was to examine the degree to which intraspecific phytochemical trait diversity influences the oviposition preference of a specialist moth. We hypothesized that chemical beta-diversity—differences in phenotypes among plants in a patch—would make it difficult for moths to select a quality host, causing decreased oviposition on preferred host plants.
We tested this hypothesis using an emerging model system for understanding how plant chemical diversity contributes to female oviposition preference in tomato host plants. We partitioned the different classes of compounds (e.g. acylsugars and terpenes) into measures of chemical dissimilarity in comparison to a focal tomato cultivar using a set of tomato genotypes created by introgressing cultivated tomato with a wild relative (Solanum pennelllii). Using a series of field and wind tunnel experiments, we manipulated tomato plants containing low (e.g. chemically similar) or high beta (e.g. chemically dissimilar) chemical diversity to examine whether the oviposition preference of females of the tomato hornworm, Manduca sexta, changes depending on the neighboring plant.
Results/Conclusions
We found that moths in the wind tunnel took longer to approach their first plant when neighbors were chemically dissimilar. Moths had a higher tendency to switch between plants if they were more chemically dissimilar. Finally, moths had a higher preference for one tomato plant variety if they were chemically different. These results suggest that chemical diversity among plants within a patch makes host selection more difficult. We corroborated the wind tunnel results in the field by surveying the M. sexta eggs on focal plants in monocultures or polycultures. Manduca sexta laid more eggs on the focal tomato cultivar over other varieties having higher concentrations of acylsugars and lower levels of sesquiterpenes. Understanding the role of plant chemical traits in the effects of plant diversity on arthropod ecology could provide insight into suppressing insect damage and slow their resistance by increasing the use of polycultures in agriculture.