SummaryHerbivore-induced plant volatiles (HIPVs) mediate critical ecological functions, but no studies have quantitatively synthesized data published on HIPVs to evaluate broad patterns. We tested three hypotheses that use eco-evolutionary theory to predict volatile induction: feeding guild (chewing arthropods > sap feeders), diet breadth (specialist herbivores > generalists), and selection history (domesticated plants < wild species).To test these hypotheses, we extracted data from 236 experiments that report volatiles produced by herbivore-damaged and undamaged plants. These data were subjected to metaanalysis, including effects on total volatiles and major biochemical classes.Overall, we found that chewers induced more volatiles than sap feeders, for both total volatiles and most volatile classes (e.g. green leaf volatiles, monoterpenes). Although specialist herbivores induced more total volatiles than generalists, this was inconsistent across chemical classes. Contrary to our expectation, domesticated species induced stronger volatile responses than wild species, even when controlling for plant taxonomy.Surprisingly, this is the first quantitative synthesis of published studies on HIPVs. Our analysis provides support for perceptions in the published literature (chewers > sap feeders), while challenging other commonly held notions (wild > crop). Despite the large number of experiments, we identified several gaps in the existing literature that should guide future investigations.

No abstract

No abstract

Synthetic plant volatile lures attract natural enemies, but may have non-target effects due to the multifunctional nature of volatile signals. For example, methyl salicylate (MeSA) is used to attract predators, yet also serves as a signaling hormone involved in plant pathogen defense. We investigated the consequences of deploying MeSA lures to attract predators for tomato (Solanum lycopersicum) defense against herbivores. To understand the spatial distribution of the lure's effect, we exposed tomatoes in the field to MeSA along a linear distance gradient and induced defenses by simulating feeding by hornworm caterpillars in a fully crossed factorial design (+/- MeSA, +/- herbivory). Subsequently, we analyzed activity of several defensive proteins (protease inhibitors, polyphenol oxidase, peroxidase), development of hornworm larvae (Manduca sexta), growth of fungal pathogens (Cladosporium and Alternaria), and attractiveness to herbivores and predators. Overall, MeSA-exposed plants were more resistant to both insects and pathogens. Secondary pathogen infection was reduced by 25% in MeSA exposed plants, possibly due to elevated polyphenol oxidase activity. Interestingly, we found that lures affected plant pathogen defenses equivalently across all distances (up to 4 m away) indicating that horizontal diffusion of a synthetic volatile may be greater than previously assumed. While thrips avoided colonizing hornworm- damaged tomato plants, this induced resistance was not observed upon pre-exposure to MeSA, suggesting that MeSA suppresses the repellant effect induced by herbivory. Thus, using MeSA lures in biological control may inadvertently protect crops from pathogens, but has mixed effects on plant resistance to insect herbivores.

Neonicotinoids from insecticidal seed coatings can contaminate soil in treated fields and adjacent areas, posing a potential risk to nontarget organisms and ecological function. To determine if cover crops can mitigate neonicotinoid contamination in treated and adjacent areas, we measured neonicotinoid concentrations for three years in no-till corn-soybean rotations, planted with or without neonicotinoid seed coatings, and with or without small grain cover crops. Although neonicotinoids were detected in cover crops, high early season dissipation provided little opportunity for winter-planted cover crops to absorb significant neonicotinoid residues; small grain cover crops failed to mitigated neonicotinoid contamination in either treated or untreated plots. As the majority of neonicotinoids from seed coatings dissipated shortly after planting, residues did not accumulate in soil, but persisted at concentrations below 5 ppb. Persistent residues could be attributed to historic neonicotinoid use and recent, nearby neonicotinoid use. Tracking neonicotinoid concentrations over time revealed a large amount of local interplot movement of neonicotinoids; in untreated plots, contamination was higher when plots were less isolated from treated plots.