Tracing the history of plant traits under domestication in cranberries: potential consequences on anti-herbivore defences

Genotypic Variation and Potential Mechanisms of Resistance against Multiple Insect Herbivores in Cranberries

Plant genotypes often exhibit varying resistance levels to herbivores. However, the impact of this genotypic variation on resistance against multiple herbivores remains poorly understood, especially in crops undergoing recent process of domestication. To address this gap, we studied the magnitude and mechanism of resistance in 12 cranberry (Vaccinium macrocarpon) genotypes to three leaf-chewing herbivores - Sparganothis fruitworm (Sparganothis sulfureana), spotted fireworm (Choristoneura parallela), and spongy moth (Lymantria dispar) - along a domestication gradient (native 'wild' genotypes, 'early hybrid' genotypes, and 'modern hybrid' genotypes). Like cranberries, S. sulfureana and C. parallela are native to the United Sates, while L. dispar is an invasive pest. We measured the survival and growth of larvae on each genotype, as well as variation in plant performance (height and biomass) and leaf defensive chemical traits (C/N ratio, total phenolics, total proanthocyanidins, and flavonols levels) in these genotypes to elucidate potential resistance mechanisms. We found differences in C. parallela and L. dispar larval performance across genotypes, with larvae performing better on the modern hybrid genotypes, while S. sulfureana showed no differences. Morphological and chemical traits varied among genotypes, with total phenolics being the only trait correlated with C. parallela and L. dispar larval performance. Notably, the wild genotypes 'McFarlin' and 'Potter' had higher total phenolics and were more resistant to both herbivores than the modern hybrids 'Demoranville' and 'Mullica Queen.' This research contributes to a comprehensive understanding of the impact of crop domestication on multiple insect herbivores, offering insights for future breeding efforts to enhance host-plant resistance against agricultural pests.

Domestication and the evolution of crops: variable syndromes, complex genetic architectures, and ecological entanglements

Domestication can be considered a specialized mutualism in which a domesticator exerts control over the reproduction or propagation (fitness) of a domesticated species to gain resources or services. The evolution of crops by human-associated selection provides a powerful set of models to study recent evolutionary adaptations and their genetic bases. Moreover, the domestication and dispersal of crops such as rice, maize, and wheat during the Holocene transformed human social and political organization by serving as the key mechanism by which human societies fed themselves. Here we review major themes and identify emerging questions in three fundamental areas of crop domestication research: domestication phenotypes and syndromes, genetic architecture underlying crop evolution, and the ecology of domestication. Current insights on the domestication syndrome in crops largely come from research on cereal crops such as rice and maize, and recent work indicates distinct domestication phenotypes can arise from different domestication histories. While early studies on the genetics of domestication often identified single large-effect loci underlying major domestication traits, emerging evidence supports polygenic bases for many canonical traits such as shattering and plant architecture. Adaptation in human-constructed environments also influenced ecological traits in domesticates such as resource acquisition rates and interactions with other organisms such as root mycorrhizal fungi and pollinators. Understanding the ecological context of domestication will be key to developing resource-efficient crops and implementing more sustainable land management and cultivation practices.

Plant Variety, Mycorrhization, and Herbivory Influence Induced Volatile Emissions and Plant Growth Characteristics in Tomato

Plants produce a range of volatile organic compounds (VOCs) that mediate vital ecological interactions between herbivorous insects, their natural enemies, plants, and soil dwelling organisms including arbuscular mycorrhizal fungi (AMF). The composition, quantity, and quality of the emitted VOCs can vary and is influenced by numerous factors such as plant species, variety (cultivar), plant developmental stage, root colonization by soil microbes, as well as the insect developmental stage, and level of specialization of the attacking herbivore. Understanding factors shaping VOC emissions is important and can be leveraged to enhance plant health and pest resistance. In this greenhouse study, we evaluated the influence of plant variety, mycorrhizal colonization, herbivory, and their interactions on the composition of emitted volatiles in tomato plants (Solanum lycopersicum L.). Four tomato varieties from two breeding histories (two heirlooms and two hybrids), were used. Tomato plants were inoculated with a commercial inoculum blend consisting of four species of AMF. Plants were also subjected to herbivory by Manduca sexta (Lepidoptera: Sphingidae L.) five weeks after transplanting. Headspace volatiles were collected from inoculated and non-inoculated plants with and without herbivores using solid phase-microextraction. Volatile profiles consisted of 21 different volatiles in detectable quantities. These included monoterpenes, sesquiterpenes, and alkane hydrocarbons. We documented a strong plant variety effect on VOC emissions. AMF colonization and herbivory suppressed VOC emissions. Plant biomass was improved by colonization of AMF. Our results show that mycorrhization, herbivory and plant variety can alter tomato plant VOC emissions and further shape volatile-mediated insect and plant interactions.

Metabolic consequences of various fruit-based diets in a generalist insect species

Most phytophagous insect species exhibit a limited diet breadth and specialize on a few or a single host plant. In contrast, some species display a remarkably large diet breadth, with host plants spanning several families and many species. It is unclear, however, whether this phylogenetic generalism is supported by a generic metabolic use of common host chemical compounds ('metabolic generalism') or alternatively by distinct uses of diet-specific compounds ('multi-host metabolic specialism')? Here, we simultaneously investigated the metabolomes of fruit diets and of individuals of a generalist phytophagous species, Drosophila suzukii, that developed on them. The direct comparison of metabolomes of diets and consumers enabled us to disentangle the metabolic fate of common and rarer dietary compounds. We showed that the consumption of biochemically dissimilar diets resulted in a canalized, generic response from generalist individuals, consistent with the metabolic generalism hypothesis. We also showed that many diet-specific metabolites, such as those related to the particular color, odor, or taste of diets, were not metabolized, and rather accumulated in consumer individuals, even when probably detrimental to fitness. As a result, while individuals were mostly similar across diets, the detection of their particular diet was straightforward. Our study thus supports the view that dietary generalism may emerge from a passive, opportunistic use of various resources, contrary to more widespread views of an active role of adaptation in this process. Such a passive stance towards dietary chemicals, probably costly in the short term, might favor the later evolution of new diet specializations.

Consequences of squash (Cucurbita argyrosperma) domestication for plant defence and herbivore interactions

MAIN CONCLUSION

Cucurbita argyrosperma domestication affected plant defence by downregulating the cucurbitacin synthesis-associated genes. However, tissue-specific suppression of defences made the cultivars less attractive to co-evolved herbivores Diabrotica balteata and Acalymma spp. Plant domestication reduces the levels of defensive compounds, increasing susceptibility to insects. In squash, the reduction of cucurbitacins has independently occurred several times during domestication. The mechanisms underlying these changes and their consequences for insect herbivores remain unknown. We investigated how Cucurbita argyrosperma domestication has affected plant chemical defence and the interactions with two herbivores, the generalist Diabrotica balteata and the specialist Acalymma spp. Cucurbitacin levels and associated genes in roots and cotyledons in three wild and four domesticated varieties were analysed. Domesticated varieties contained virtually no cucurbitacins in roots and very low amounts in cotyledons. Contrastingly, cucurbitacin synthesis-associated genes were highly expressed in the roots of wild populations. Larvae of both insects strongly preferred to feed on the roots of wild squash, negatively affecting the generalist's performance but not that of the specialist. Our findings illustrate that domestication results in tissue-specific suppression of chemical defence, making cultivars less attractive to co-evolved herbivores. In the case of squash, this may be driven by the unique role of cucurbitacins in stimulating feeding in chrysomelid beetles.

Herbivory Damage Increased VOCs in Wild Relatives of Murtilla Plants Compared to Their First Offspring

Murtilla (Ugni molinae) is a shrub native to Chile that has undergone an incipient domestication process aimed at increasing its productivity. The reduction in intrinsic chemical defenses due to the domestication process has resulted in a decrease in the plant's ability to defend itself against mechanical or insect damage. In response to this damage, plants release volatile organic compounds (VOCs) as a means of defense. To understand how domestication has impacted the production of VOCs in the first offspring of murtilla, we hypothesized that their levels would be reduced due to the induction of mechanical and herbivore damage. To test this hypothesis, we collected VOCs from four offspring ecotypes and three wild relatives of murtilla. We induced mechanical and herbivore damage in the plants and then enclosed them in a glass chamber, where we captured the VOCs. We identified 12 compounds using GC-MS. Our results showed that wild relative ecotypes had a higher VOC release rate of 624.6 µg/cm²/day. Herbivore damage was the treatment that produced the highest release of VOCs, with 439.3 µg/cm²/day in wild relatives. These findings suggest that herbivory triggers defenses through the emission of VOCs, and that domestication has influenced the production of these compounds in murtilla. Overall, this study contributes to bridging the gap in the incipient domestication history of murtilla and highlights the importance of considering the impact of domestication on a plant's chemical defenses.

The effects of plant domestication on the foraging and performance of parasitoids

Domestication-related changes in the chemical traits of crop plants affect parasitoid foraging success, development, and survival. For example, herbivore-induced changes in the production of volatiles by domesticated plants can enhance or reduce parasitoid attraction. While the trade-off between nutrient content and chemical defense in cultivated plants can increase the suitability of hosts for parasitoids, their increased health and size can positively affect their immune response against parasitoids. Overall, plant domestication is expected to significantly affect their relationship with parasitoids due to altered plant morphology, physical characteristics, chemical defenses, and new plant associations. This review highlights the need for research on the effects of plant domestication on host-parasitoid interactions in the interest of better controlling insect pests.

Plant genetic relatedness and volatile-mediated signalling between Solanum tuberosum plants in response to herbivory by Spodoptera exigua

It has been proposed that plant-plant signalling via herbivore-induced volatile organic compounds (VOCs) should be stronger between closely related than unrelated plants. However, empirical tests remain limited and few studies have provided detailed assessments of induced changes in VOCs emissions across plant genotypes to explain genetic relatedness effects. In this study, we tested whether airborne signalling in response to herbivory between Solanum tuberosum (potato) plants was contingent on plant genetic relatedness, and further investigated genotypic variation in VOCs potentially underlying signalling and its contingency on relatedness. We carried out a greenhouse experiment using 15 S. tuberosum varieties placing pairs of plants in plastic cages, i.e. an emitter and a receiver, where both plants were of the same genotype or different genotype thereby testing for self-recognition, an elemental form genetic relatedness effects. Then, for half of the cages within each level of relatedness the emitter plant was damaged by Spodoptera exigua larvae whereas for the other half the emitter was not damaged. Three days later, we placed S. exigua larvae on receivers to test for emitter VOC effects on leaf consumption and larval weight gain (i.e. induced resistance). In addition, we used a second group of plants subjected to the same induction treatment with the same S. tuberosum varieties to test for herbivore-induced changes in VOC emissions and variation in VOC emissions among these plant genotypes. We found that herbivory drove changes in VOC composition but not total emissions, and also observed quantitative and qualitative variation in constitutive and induced VOC emissions among varieties. Results from the bioassay showed that the amount of leaf area consumed and larval weight gain on receiver plants exposed to damaged emitters were significantly lower compared to mean values on receivers exposed to control emitters. However, and despite genotypic variation in induced VOCs, this signalling effect was not contingent on plant genetic relatedness. These findings provide evidence of VOCs-mediated signalling between S. tuberosum plants in response to S. exigua damage, but no evidence of self-recognition effects in signalling contingent on variation in VOC emissions among S. tuberosum varieties.

Root volatile profiles and herbivore preference are mediated by maize domestication, geographic spread, and modern breeding

Domestication affected the abundances and diversity of maize root volatiles more than northward spread and modern breeding, and herbivore preference for roots was correlated with volatile diversity and herbivore resistance. Studies show that herbivore defenses in crops are mediated by domestication, spread, and breeding, among other human-driven processes. They also show that those processes affected chemical communication between crop plants and herbivores. We hypothesized that (i) preference of the herbivore (Diabrotica virgifera virgifera) larvae for embryonic roots of maize (Zea mays mays) would increase and (ii) root volatile diversity would decrease with the crop's domestication, northward spread to present-day USA, and modern breeding. We used Balsas teosinte (Zea mays parviglumis), Mexican and USA landrace maizes, and US inbred maize lines to test these hypotheses. We found that herbivore preference and volatile diversity increased with maize domestication and northward spread but decreased with modern breeding. Additionally, we found that the abundances of single volatiles did not consistently increase or decrease with maize domestication, spread, and breeding; rather, volatiles grouped per their abundances were differentially affected by those processes, and domestication had the greatest effects. Altogether, our results suggested that: the herbivore's preference for maize roots is correlated with volatile diversity and herbivore resistance; changes in abundances of individual volatiles are evident at the level of volatile groups; and maize domestication, but not spread and breeding, affected the abundances of some green leaf volatiles and sesquiterpenes/sesquiterpenoids. In part, we discussed our results in the context of herbivore defense evolution when resources for plant growth and defense vary across environments. We suggested that variability in relative abundance of volatiles may be associated with their local, functional relevance across wild and agricultural environments.

Wild potato ancestors as potential sources of resistance to the aphid Myzus persicae

BACKGROUND

Plant resistance to insects can be reduced by crop domestication which means their wild ancestors could provide novel sources of resistance. Thus, crossing wild ancestors with domesticated crops can potentially enhance their resistance against insects. However, a prerequisite for this is identification of sources of resistance. Here, we investigated the response of three wild potato (Solanum stoloniferum Schltdl.) accessions and cultivated potato (Solanum tuberosum) to aphid (Myzus persicae Sulzer) herbivory.

RESULTS

Results revealed that there was a significant reduction in aphid survival and reproduction on wild potato accessions (CGN18333, CGN22718, CGN23072) compared to cultivated (Desiree) potato plants. A similar trend was observed in olfactometer bioassay; the wild accessions had a repellent effect on adult aphids. In contrast, among the tested wild potato accessions, the parasitoid Diaeretiella rapae (M'Intosh) was significantly attracted to volatiles from CGN18333. Volatile analysis showed that wild accessions emitted significantly more volatiles compared to cultivated potato. Principal component analysis (PCA) of volatile data revealed that the volatile profiles of wild and cultivated potato are dissimilar. β-Bisabolene, (E)-β-farnesene, trans-α-bergamotene, d-limonene, (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT), and p-cymen-7-ol were the main volatiles contributing to the emitted blends, suggesting possible involvement in the behavioural response of both M. persicae and D. rapae.

CONCLUSION

Our findings show that the tested wild accessions have the potential to be used to breed aphid-resistant potatoes. This opens new opportunities to reduce the aphid damage and to enhance the recruitment of natural enemies. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Selection for seed size has uneven effects on specialized metabolite abundance in oat (Avena sativa L.)

Plant breeding strategies to optimize metabolite profiles are necessary to develop health-promoting food crops. In oats (Avena sativa L.), seed metabolites are of interest for their antioxidant properties, yet have not been a direct target of selection in breeding. In a diverse oat germplasm panel spanning a century of breeding, we investigated the degree of variation of these specialized metabolites and how it has been molded by selection for other traits, like yield components. We also ask if these patterns of variation persist in modern breeding pools. Integrating genomic, transcriptomic, metabolomic, and phenotypic analyses for three types of seed specialized metabolites—avenanthramides, avenacins, and avenacosides—we found reduced heritable genetic variation in modern germplasm compared with diverse germplasm, in part due to increased seed size associated with more intensive breeding. Specifically, we found that abundance of avenanthramides increases with seed size, but additional variation is attributable to expression of biosynthetic enzymes. In contrast, avenacoside abundance decreases with seed size and plant breeding intensity. In addition, these different specialized metabolites do not share large-effect loci. Overall, we show that increased seed size associated with intensive plant breeding has uneven effects on the oat seed metabolome, but variation also exists independently of seed size to use in plant breeding. This work broadly contributes to our understanding of how plant breeding has influenced plant traits and tradeoffs between traits (like growth and defense) and the genetic bases of these shifts.

The effect of squash domestication on a belowground tritrophic interaction

The domestication of plants has commonly resulted in the loss of plant defense metabolites, with important consequences for the plants' interactions with herbivores and their natural enemies. Squash domestication started 10'000 years ago and has led to the loss of cucurbitacins, which are highly toxic triterpenes. The banded cucumber beetle (Diabrotica balteata), a generalist herbivore, is adapted to feed on plants from the Cucurbitaceae and is known to sequester cucurbitacins, supposedly for its own defense. However, the evidence for this is inconclusive. In this study we tested the impact of squash domestication on the chemical protection of D. balteata larvae against a predatory rove beetle (Dalotia coriaria). We found that cucurbitacins do not defend the larvae against this common soil dwelling predator. In fact, D. balteata larvae were less attacked when they fed on cucurbitacin-free roots of domesticated varieties compared to high-cucurbitacin roots of wild plants. This study appears to be the first to look at the consequences of plant domestication on belowground tritrophic interactions. Our results challenge the generalized assumption that sequestered cucurbitacins protect this herbivore against natural enemies, and instead reveals an opposite effect that may be due to a tradeoff between coping with cucurbitacins and avoiding predation.

Molecular ecology of plant volatiles in interactions with insect herbivores

Plant-derived volatile organic compounds (VOCs) play pivotal roles in interactions with insect herbivores. Individual VOCs can be directly toxic or deterrent, serve as signal molecules to attract natural enemies, and/or be perceived by distal plant tissues as a priming signal to prepare for expected herbivory. Environmental conditions, as well as the specific plant-insect interaction being investigated, strongly influence the observed functions of VOC blends. The complexity of plant-insect chemical communication via VOCs is further enriched by the sophisticated molecular perception mechanisms of insects, which can respond to one or more VOCs and thereby influence insect behavior in a manner that has yet to be fully elucidated. Despite numerous gaps in the current understanding of VOC-mediated plant-insect interactions, successful pest management strategies such as push-pull systems, synthetic odorant traps, and crop cultivars with modified VOC profiles have been developed to supplement chemical pesticide applications and enable more sustainable agricultural practices. Future studies in this field would benefit from examining the responses of both plants and insects in the same experiment to gain a more complete view of these interactive systems. Furthermore, a molecular evolutionary study of key genetic elements of the ecological interaction phenotypes could provide new insights into VOC-mediated plant communication with insect herbivores.

Resistance and Not Plant Fruit Traits Determine Root-Associated Bacterial Community Composition along a Domestication Gradient in Tomato

Soil bacterial communities are involved in multiple ecosystem services, key in determining plant productivity. Crop domestication and intensive agricultural practices often disrupt species interactions with unknown consequences for rhizosphere microbiomes. This study evaluates whether variation in plant traits along a domestication gradient determines the composition of root-associated bacterial communities; and whether these changes are related to targeted plant traits (e.g., fruit traits) or are side effects of less-often-targeted traits (e.g., resistance) during crop breeding. For this purpose, 18 tomato varieties (wild and modern species) differing in fruit and resistance traits were grown in a field experiment, and their root-associated bacterial communities were characterised. Root-associated bacterial community composition was influenced by plant resistance traits and genotype relatedness. When only considering domesticated tomatoes, the effect of resistance on bacterial OTU composition increases, while the effect due to phylogenetic relatedness decreases. Furthermore, bacterial diversity positively correlated with plant resistance traits. These results suggest that resistance traits not selected during domestication are related to the capacity of tomato varieties to associate with different bacterial groups. Taken together, these results evidence the relationship between plant traits and bacterial communities, pointing out the potential of breeding to affect plant microbiomes.

Effects of elevated ozone on the emission of volatile isoprenoids from flowers and leaves of rose (Rosa sp.) varieties

Tropospheric ozone (O₃) affects isoprenoid emissions, and floral emissions in particular, which may result in potential impacts on the interactions of plants with other organisms. The effects of ozone (O₃) on isoprenoid emissions have been investigated for many years, while knowledge on O₃ effects on floral emissions is still scarce and the relevant mechanism has not been clarified so far. We investigated the effects of O₃ on floral and foliar isoprenoid emissions (mainly isoprene, monoterpenes and sesquiterpenes) and their synthase substrates from three rose varieties (CH, Rosa chinensis Jacq. var. chinensis; SA, R. hybrida 'Saiun'; MO, R. hybrida 'Monica Bellucci') at different exposure durations. Results indicated that the O₃-induced stimulation after short-term exposure (35 days after the beginning of O₃ exposure) was significant only for sesquiterpene emissions from flowers, while long-term O₃ exposure (90 days after the beginning of O₃ exposure) significantly decreased both foliar and floral monoterpene and sesquiterpene emissions. In addition, the observed decline of emissions under long-term O₃ exposure resulted from the limitation of synthase substrates, and the responses of emissions and substrates varied among varieties, with the greatest variation in the O₃-sensitive variety. These findings provide important insights on plant isoprenoid emissions and species selection for landscaping, especially in areas with high O₃ concentration.

Influence of wild, local and cultivated tobacco varieties on the oviposition preference and offspring performance of Spodoptera litura

The influences of different plants on herbivores have recently attracted research interest; however, little is known regarding the effects of wild, local and cultivated varieties of the same plant from the same origin on herbivores. This study aimed to examine the effects of different tobacco varieties from the same origin on the oviposition preference and offspring performance of Spodoptera litura. We selected two wild ('Bishan wild tobacco' and 'Badan wild tobacco'), two local ('Liangqiao sun-cured tobacco' and 'Shuangguan sun-cured tobacco') and two cultivated ('Xiangyan No. 5' and 'Cunsanpi') tobacco varieties from Hunan Province, China. We found that female S. litura varied in oviposition preferences across the tobacco varieties. They preferred to lay eggs on the cultivated varieties, followed by the local varieties, with the wild varieties being the least preferred. Furthermore, different tobacco varieties significantly influenced the life history parameters of S. litura. Survival rate, pupal weight, emergence rate and adult dry weight decreased in the following order: cultivated varieties > local varieties > wild varieties. Conversely, the pupal stage and development period decreased in the following order: wild varieties > local varieties > cultivated varieties. Therefore, we conclude that wild tobacco varieties have higher resistance to S. litura than cultivated and local varieties, reflecting the evolutionary advantages of wild tobacco varieties.

Maize biochemistry in response to root herbivory was mediated by domestication, spread, and breeding

With domestication, northward spread, and breeding, maize defence against root-herbivores relied on induced defences, decreasing levels of phytohormones involved in resistance, and increasing levels of a phytohormone involved in tolerance. We addressed whether a suite of maize (Zea mays mays) phytohormones and metabolites involved in herbivore defence were mediated by three successive processes: domestication, spread to North America, and modern breeding. With those processes, and following theoretical predictions, we expected to find: a change in defence strategy from reliance on induced defences to reliance on constitutive defences; decreasing levels of phytohormones involved in herbivore resistance, and; increasing levels of a phytohormone involved in herbivore tolerance. We tested those predictions by comparing phytohormone levels in seedlings exposed to root herbivory by Diabrotica virgifera virgifera among four plant types encompassing those processes: the maize ancestor Balsas teosinte (Zea mays parviglumis), Mexican maize landraces, USA maize landraces, and USA inbred maize cultivars. With domestication, maize transitioned from reliance on induced defences in teosinte to reliance on constitutive defences in maize, as predicted. One subset of metabolites putatively involved in herbivory defence (13-oxylipins) was suppressed with domestication, as predicted, though another was enhanced (9-oxylipins), and both were variably affected by spread and breeding. A phytohormone (indole-3-acetic acid) involved in tolerance was enhanced with domestication, and with spread and breeding, as predicted. These changes are consistent with documented changes in herbivory resistance and tolerance, and occurred coincidentally with cultivation in increasingly resource-rich environments, i.e., from wild to highly enriched agricultural environments. We concluded that herbivore defence evolution in crops may be mediated by processes spanning thousands of generations, e.g., domestication and spread, as well as by processes spanning tens of generations, e.g., breeding and agricultural intensification.

Application of Plant Defense Elicitors Fails to Enhance Herbivore Resistance or Mitigate Phytoplasma Infection in Cranberries

Synthetic elicitors of the salicylic acid (SA) and jasmonic acid (JA) plant defense pathways can be used to increase crop protection against herbivores and pathogens. In this study, we tested the hypothesis that elicitors of plant defenses interact with pathogen infection to influence crop resistance against vector and nonvector herbivores. To do so, we employed a trophic system comprising of cranberries (Vaccinium macrocarpon), the phytoplasma that causes false blossom disease, and two herbivores-the blunt-nosed leafhopper (Limotettix vaccinii), the vector of false blossom disease, and the nonvector gypsy moth (Lymantria dispar). We tested four commercial elicitors, including three that activate mainly SA-related plant defenses (Actigard, LifeGard, and Regalia) and one activator of JA-related defenses (Blush). A greenhouse experiment in which phytoplasma-infected and uninfected plants received repeated exposure to elicitors revealed that both phytoplasma infection and elicitor treatment individually improved L. vaccinii and L. dispar mass compared to uninfected, untreated controls; however, SA-based elicitor treatments reduced L. vaccinii mass on infected plants. Regalia also improved L. vaccinii survival. Phytoplasma infection reduced plant size and mass, increased levels of nitrogen (N) and SA, and lowered carbon/nitrogen (C/N) ratios compared to uninfected plants, irrespective of elicitor treatment. Although none of our elicitor treatments influenced transcript levels of a phytoplasma-specific marker gene, all of them increased N and reduced C/N levels; the three SA activators also reduced JA levels. Taken together, our findings reveal positive effects of both phytoplasma infection and elicitor treatment on the performance of L. vaccinii and L. dispar in cranberries, likely via enhancement of plant nutrition and changes in phytohormone profiles, specifically increases in SA levels and corresponding decreases in levels of JA. Thus, we found no evidence that the tested elicitors of plant defenses increase resistance to insect herbivores or reduce disease incidence in cranberries.

Intentional and unintentional selection during plant domestication: herbivore damage, plant defensive traits and nutritional quality of fruit and seed crops

Greater susceptibility to herbivory can arise as an effect of crop domestication. One proposed explanation is that defenses decreased intentionally or unintentionally during the domestication process, but evidence for this remains elusive. An alternative but nonexclusive explanation is presumed selection for higher nutritional quality. We used a metaanalytical approach to examine susceptibility to herbivores in fruit and seed crops and their wild relatives. Our analyses provide novel insights into the mechanisms of increased susceptibility by evaluating whether it can be attributed to either a reduction in herbivore defensive traits, including direct/indirect and constitutive/inducible defenses, or an increase in the nutritional content of crops. The results confirm higher herbivory and lower levels of all types of defenses in crops compared to wild relatives, although indirect defenses were more affected than direct ones. Contrary to expectations, nutritional quality was lower in crops than in wild relatives, which may enhance biomass loss to herbivores if they increase consumption to meet nutritional requirements. Our findings represent an important advance in our understanding of how changes in defensive and nutritional traits following domestication could influence, in combination or individually, crop susceptibility to herbivore attacks.

Domestication of Plants of Ugni molinae Turcz (Myrtaceae) Interferes in the Biology of Chilesia rudis (Lepidoptera: Erebidae) Larvae

In terms of the domestication process in murtilla, studies have found changes in the concentration of phenolic compounds, with reduction of chemical defense of plants, depending on the change in the feeding behavior of insects. Thus, we hypothesized that the domestication of Ugni molinae decreases the content of phenolic compounds and modifies the feeding preference of Chilesia rudis larvae. Leaves of three parental ecotypes and four cultivated ecotypes were used in preference experiments to evaluate the mass gain and leaves consumption of larvae. Phenolic extracts from leaves of U. molinae were analyzed by HPLC. Identified compounds were incorporated in an artificial diet to assess their effect on mass gain, consumption, and survival of the larvae. The presence of phenolic compounds in bodies and feces was also evaluated. In terms of choice assays, larvae preferred parental ecotypes. Regarding compounds, vanillin was the most varied between the ecotypes in leaves. However, plant domestication did not show a reduction in phenolic compound concentration of the ecotypes studied. Furthermore, there was no clear relation between phenolic compounds and the performance of C. rudis larvae. Whether this was because of sequestration of some compounds by larvae is unknown. Finally, results of this study could also suggest that studied phenolic compounds have no role in the C. rudis larvae resistance in this stage of murtilla domestication process.

Resource allocation strategies among vegetative growth, sexual reproduction, asexual reproduction and defense during growing season of Aconitum kusnezoffii Reichb

Natural plants must actively allocate their limited resources for survival and reproduction. Although vegetative growth, sexual reproduction, asexual reproduction and defense are all basic processes in the life cycle of plants, the strategies used to allocate resources between these processes are poorly understood. These processes are conspicuous in naturally grown Aconitum kusnezoffii Reichb., which makes it a suitable study subject. Here, the morphology, dry matter, total organic carbon, total nitrogen and aconitum alkaloid levels of shoot, principal root (PR) and lateral roots were measured throughout the growing season. Then, transcriptome and metabolite content analyses were performed. We found that vegetative growth began first. After vegetative growth ceased, sexual development began. Flower organ development was accompanied by increased photosynthesis and the PR consumed temporarily stored resources after flower formation. Asexual propagule development initiated earlier than sexual reproduction and kept accumulating resources after that. Development was slow before flower formation, mainly manifesting as increasing length; then, after flower formation it accelerated via enhanced material transport and accumulation. Defense compounds were maintained at low levels before flowering. In particular, the turnover of defense compounds was enhanced before and after flower bud emergence, providing resources for other processes. After flower formation, defense compounds were accumulated. The pattern found herein provides a vivid example for further studies on resource allocation strategies. The exciting finding that the PR, as a more direct storage site for photosynthate, is a buffer unit for resources, and that defense compounds can be reused for other processes, suggests a need to explore potential mechanisms.

Life History and Damage by Systena frontalis F. (Coleoptera: Chrysomelidae) on Vaccinium macrocarpon Ait

Pest management of emerging pests can be challenging because very little fundamental knowledge is available to inform management strategies. One such pest, the red-headed flea beetle Systena frontalis (Fabricius) (Coleoptera: Chrysomelidae), is increasingly being identified as a pest of concern in cranberries Vaccinium macrocarpon Aiton (Ericales: Ericaceae). To improve our understanding of this pest and to develop more targeted management programs, we conducted field and laboratory studies to characterize the development, seasonal emergence patterns, and density-dependent plant injury. We found that significantly more flea beetle eggs hatched when exposed to sustained cold treatment between 0 and 5°C for 15 wk than at warmer temperatures, and for shorter and longer cold-period durations. The adults emerged sporadically over the summer, were patchily distributed, fed on both fruit and foliage, and preferentially fed on new plant growth. Using soil cores, we found eggs and larvae located relatively deep (>30 cm) in the soil. These patterns indicate that S. frontalis likely overwinters as eggs, and that targeting the larval stage may be the most effective management approach. Despite the cryptic nature of the larvae, continuing to improve our understanding of this life stage will be critical to optimizing control strategies.

The Effects of Ozone on Herbivore-Induced Volatile Emissions of Cultivated and Wild Brassica Rapa

Since preindustrial times, concentrations of tropospheric ozone, a phytotoxic pollutant, have risen in the Northern Hemisphere. Selective breeding has intentionally modified crop plant traits to improve yield but may have altered plant defenses against abiotic and biotic stresses. This study aims to determine if cultivated and wild plants respond differently to herbivory under elevated ozone. We studied the volatile emissions of four cultivated Brassica rapa ssp. oleifera varieties and one wild population after exposure to ozone or Plutella xylostella larval feeding either individually or together. Ozone modulated the volatiles emitted in response to herbivory by all plant varieties to different extents. We did not observe a clear difference in the effects of ozone on wild and cultivated plants, but cultivated plants had higher volatile emission rates in response to herbivory and ozone had either no effect or increased the herbivore-induced response. Larvae tended to feed more on elevated ozone-treated plants; however, we could not link the increase of feeding to the change in volatile emissions. Our study complements recent studies reporting that selective breeding might not have weakened chemical defenses to biotic and abiotic stresses of cultivated plants.

Herbivory and anti-herbivore defences in wild and cultivated Cnidoscolus aconitifolius: disentangling domestication and environmental effects

Phenotypic changes in plants during domestication may disrupt plant-herbivore interactions. Because wild and cultivated plants have different habitats and some anti-herbivore defences exhibit some plasticity, their defences may be also influenced by the environment. Our goal was to assess the effects of domestication and the environment on herbivory and some anti-herbivore defences in chaya (Cnidoscolus aconitifolius) in its centre of domestication. Herbivores, herbivory, and direct and indirect anti-herbivore defences were assessed in wild and cultivated plants. The same variables were measured in the field and in a common garden to assess environmental effects. Our results show that domestication increased herbivory and herbivore abundance, but reduced direct and some indirect defences (ants). The environment also affected the herbivore guild (herbivore abundance and richness) and some direct and indirect defences (trichome number and ants). There was also an interaction effect of domestication and the environment on the number of trichomes. We conclude that domestication and the environment influence herbivory and anti-herbivore defences in an additive and interactive manner in chaya.

Shoot Characterization of Isoprene and Ocimene-Emitting Transgenic Arabidopsis Plants under Contrasting Environmental Conditions

Isoprenoids are among the most abundant biogenic volatile compounds (VOCs) emitted by plants, and mediate both biotic and abiotic stress responses. Here, we provide for the first time a comparative analysis of transgenic Arabidopsis lines constitutively emitting isoprene and ocimene. Transgenic lines and Columbia-0 (Col-0) Arabidopsis were characterized under optimal, water stress, and heat stress conditions. Under optimal conditions, the projected leaf area (PLA), relative growth rate, and final dry weight were generally higher in transgenics than Col-0. These traits were associated to a larger photosynthetic capacity and CO2 assimilation rate at saturating light. Isoprene and ocimene emitters displayed a moderately higher stress tolerance than Col-0, showing higher PLA and gas-exchange traits throughout the experiments. Contrasting behaviors were recorded for the two overexpressors under water stress, with isoprene emitters showing earlier stomatal closure (conservative behavior) than ocimene emitters (non-conservative behavior), which might suggest different induced strategies for water conservation and stress adaptation. Our work indicates that (i) isoprene and ocimene emitters resulted in enhanced PLA and biomass under optimal and control conditions and that (ii) a moderate stress tolerance is induced when isoprene and ocimene are constitutively emitted in Arabidopsis, thus providing evidence of their role as a potential preferable trait for crop improvement.

Identification of Key Aroma Compounds in Cranberry Juices as Influenced by Vinification

This study aimed to identify the key aroma-active volatiles in cranberry wines through three vinification methods (White, Red and Thermo) using GC-MS/O to identify the important aroma compounds. A total of 70 compounds were detected, with 67 in wines and 61 in juices. The esters was the most diversified class, while alcohols and acids were the most abundant, especially 3-methylbutanol, methylbutyric acid, and benzoic acid. The volatile profiles of cranberry wines are distinctive from their source juices. Most alcohols, esters, and acids are fermentation-derived, while terpenes, phenols, aldehydes and ketones are varietal. The Red vinification retained the most varietal volatiles from the must, while the White and Thermo vinifications produced more volatiles during fermentation. Thermovinification reduced the yield of benzoic acid and its derivatives after fermentation. Olfactory analysis identified 47 aroma-active compounds, among which 41 were considered as the major aroma contributors (ethyl benzoate had the highest modified detection frequency).

Balancing Disturbance and Conservation in Agroecosystems to Improve Biological Control

Disturbances associated with agricultural intensification reduce our ability to achieve sustainable crop production. These disturbances stem from crop-management tactics and can leave crop fields more vulnerable to insect outbreaks, in part because natural-enemy communities often tend to be more susceptible to disturbance than herbivorous pests. Recent research has explored practices that conserve natural-enemy communities and reduce pest outbreaks, revealing that different components of agroecosystems can influence natural-enemy populations. In this review, we consider a range of disturbances that influence pest control provided by natural enemies and how conservation practices can mitigate or counteract disturbance. We use four case studies to illustrate how conservation and disturbance mitigation increase the potential for biological control and provide co-benefits for the broader agroecosystem. To facilitate the adoption of conservation practices that improve top-down control across significant areas of the landscape, these practices will need to provide multifunctional benefits, but should be implemented with natural enemies explicitly in mind.

A Return to the Wild: Root Exudates and Food Security

Challenges to food security under conditions of global change are forcing us to increase global crop production. Focussing on belowground plant traits, especially root exudation, has great promise to meet this challenge. Root exudation is the release of a vast array of compounds into the soil. These exudates are involved in many biotic and abiotic interactions. Wild relatives of crops provide a large potential source of information and genetic material and have desirable traits that could be incorporated into modern breeding programs. However, root exudates are currently underexploited. Here, we highlight how the traits of root exudates of crop wild relatives could be used to improve agricultural output and reduce environmental impacts, particularly by decreasing our dependence on pesticides and fertilisers.

Resistance and Tolerance to Root Herbivory in Maize Were Mediated by Domestication, Spread, and Breeding

Plants may defend against herbivory and disease through various means. Plant defensive strategies against herbivores include resistance and tolerance, which may have metabolic costs that affect plant growth and reproduction. Thus, expression of these strategies may be mediated by a variety of factors, such as resource availability, herbivory pressure, and plant genetic variation, among others. Additionally, artificial selection by farmers and systematic breeding by scientists may mediate the expression of resistance and tolerance in crop plants. In this study, we tested whether maize defense against Western corn rootworm (WCR) was mediated by the crop's domestication, spread, and modern breeding. We expected to find a trend of decreasing resistance to WCR with maize domestication, spread, and breeding, and a trend of increasing tolerance with decreasing resistance. To test our expectations, we compared resistance and tolerance among four Zea plants spanning those processes: Balsas teosinte, Mexican landrace maize, US landrace maize, and US inbred maize. We measured the performance of WCR larvae as a proxy for plant resistance, and plant growth as affected by WCR feeding as a proxy for plant tolerance. Our results showed that domestication and spread decreased maize resistance to WCR, as expected, whereas breeding increased maize resistance to WCR, contrary to expected. Our results also showed that maize resistance and tolerance to WCR are negatively correlated, as expected. We discussed our findings in relation to ecological-evolutionary hypotheses seeking to explain defense strategy evolution in the contexts of plant resistance-productivity trade-offs, plant tolerance-resistance trade-offs, and varying resource availability vis-à-vis plant physiological stress and herbivory pressure. Finally, we suggested that defense strategy evolution in maize, from domestication to the present, is predicted by those ecological-evolutionary hypotheses.

Balance between nitrogen use efficiency and cadmium tolerance in Brassica napus and Arabidopsis thaliana

The transmembrane transport of NO₃^- and Cd²⁺ into plant cell vacuoles relies on the energy from their tonoplast proton pumps, V-ATPase and V-PPase. If the activity of these pumps is reduced, it results in less NO₃^- and Cd²⁺ being transported into the vacuoles, which contributes to better nitrogen use efficiency (NUE) and lower Cd²⁺ tolerance in plants. The physiological mechanisms that regulate the balance between NUE and Cd²⁺ tolerance remain unknown. In our study, two Brassica napus genotypes with differential NUEs, xiangyou 15 and 814, and Atclca-2 mutant and AtCAX4 over-expression line (AtCAX4-OE) of Arabidopsis thaliana, were used to investigate Cd²⁺ stress responses. We found that the Brassica napus genotype, with higher NUE, was more sensitive to Cd²⁺ stress. The AtCAX4-OE mutant, with higher Cd²⁺ vacuolar sequestration capacity (VSC), limited NO₃^- sequestration into root vacuoles and promoted NUE. Atclca-2 mutants, with decreased NO₃^- VSC, enhanced Cd²⁺ sequestration into root vacuoles and conferred greater Cd²⁺ tolerance than the WT. This may be due to the competition between Cd²⁺ andNO₃^- in the vacuoles for the energy provided by V-ATPase and V-PPase. Regulating the balance between Cd²⁺ and NO₃^- vacuolar accumulation by inhibiting the activity of CLCa transporter and increasing the activity of CAX4 transporter will simultaneously enhance both the NUE and Cd²⁺ tolerance of Brassica napus, essential for improving its Cd²⁺ phytoremediation potential.

Resource allocation trade-offs and the loss of chemical defences during apple domestication

BACKGROUND AND AIMS

Most crops have been dramatically altered from their wild ancestors with the primary goal of increasing harvestable yield. A long-held hypothesis is that increased allocation to yield has reduced plant investment in defence and resulted in crops that are highly susceptible to pests. However, clear demonstrations of these trade-offs have been elusive due to the many selective pressures that occur concurrently during crop domestication.

METHODS

To provide a robust test of whether increased allocation to yield can alter plant investment in defence, this study examined fruit chemical defence traits and herbivore resistance across 52 wild and 56 domesticated genotypes of apples that vary >26-fold in fruit size. Ninety-six phenolic metabolites were quantified in apple skin, pulp and seeds, and resistance to the codling moth was assessed with a series of bioassays.

KEY RESULTS

The results show that wild apples have higher total phenolic concentrations and a higher diversity of metabolites than domesticated apples in skin, pulp and seeds. A negative phenotypic relationship between fruit size and phenolics indicates that this pattern is driven in part by allocation-based trade-offs between yield and defence. There were no clear differences in codling moth performance between wild and domesticated apples and no overall effects of total phenolic concentration on codling moth performance, but the results did show that codling moth resistance was increased in apples with higher phenolic diversity. The concentrations of a few individual compounds (primarily flavan-3-ols) also correlated with increased resistance, primarily driven by a reduction in pupal mass of female moths.

CONCLUSIONS

The negative phenotypic relationship between fruit size and phenolic content, observed across a large number of wild and domesticated genotypes, supports the hypothesis of yield-defence trade-offs in crops. However, the limited effects of phenolics on codling moth highlight the complexity of consequences that domestication has for plant-herbivore interactions. Continued studies of crop domestication can further our understanding of the multiple trade-offs involved in plant defence, while simultaneously leading to novel discoveries that can improve the sustainability of crop production.

Genotypic Variation and Phenotypic Plasticity in Gene Expression and Emissions of Herbivore-Induced Volatiles, and their Potential Tritrophic Implications, in Cranberries

Herbivorous insects are important problems in cranberry (Vaccinium macrocarpon Ait.) production. The use of chemical pesticides is common practice, but beneficial insects such as natural enemies of herbivores (e.g. predators and parasitoids) could be affected as well. Therefore, we studied the defensive mechanisms that cranberry plants use to combat pests, focusing on herbivore-induced plant volatiles (HIPVs), which can be used to recruit predators and parasitoids foraging for prey or hosts. Then, we used synthetic HIPVs to test the attraction of natural enemies. In a greenhouse, we assessed nine cranberry genotypes for expression of genes involved in HIPV biosynthesis and/or emission of HIPVs. In an experimental field, we assessed whether baiting traps with individual or combinations of HIPVs increased attractiveness to natural enemies. The results showed that different cranberry genotypes vary in their emission of monoterpenes and sesquiterpenes but not in their expression of two genes associated with terpene biosynthesis, α-humulene/β-caryophyllene synthase and (3S,6E)-nerolidol/R-linalool synthase. Induction with methyl jasmonate or herbivore (gypsy moth, Lymantria dispar L.) feeding increased the expression of these genes and emission of HIPVs. The HIPV methyl salicylate (MeSA), alone or in combination with other HIPVs, increased syrphid attraction by 6-fold in the field, while (Z)-3-hexenyl acetate and MeSA repelled ladybeetles and megaspilids, respectively. Linalool and β-caryophyllene elicited no behavioral responses of natural enemies. Elucidating the mechanisms of pest resistance, as well as experimentally augmenting plant defenses such as HIPVs, may contribute to the development of more sustainable pest management practices in crops, including cranberries.

Does enhanced nutrient availability increase volatile emissions in cranberry?

Nutrient availability impacts plant indirect defenses, such as emissions of herbivore-induced plant volatiles (HIPVs) that attract natural enemies of herbivores. However, the effects are variable depending on the cropping system, and emissions may increase, decrease, or be not affected by nutrient availability. Here, we evaluated the effects of different fertilizer regimes, which varied nitrogen (N), phosphorus (P), and potassium (K) availability, on HIPV emissions in cranberry, Vaccinium macrocarpon Ait. Plants included six cranberry varieties that were subjected to four different fertilizer regimes and either noninduced or induced with methyl jasmonate (MeJA), an elicitor of HIPVs, in a 6 × 4 × 2 factorial design. Results show that enhanced NPK fertilizer applications increased total HIPV emissions in MeJA-treated cranberries, regardless of variety. This effect was due to an increase in plant fresh weight. Although the ecological effects of increased HIPV emissions need to be investigated, these findings may have implications for natural enemy manipulation in agro-ecosystems.

Differential Susceptibility of Wild and Cultivated Blueberries to an Invasive Frugivorous Pest

Highbush blueberry is a crop native to the northeast USA that has been domesticated for about 100 years. This study compared the susceptibility of wild and domesticated/cultivated highbush blueberries to an invasive frugivorous pest, the spotted wing drosophila (Drosophila suzukii). We hypothesized that: 1) cultivated fruits are preferred by D. suzukii for oviposition and better hosts for its offspring than wild fruits; and, 2) wild and cultivated fruits differ in physico-chemical traits. Fruits from wild and cultivated blueberries were collected from June through August of 2015 and 2016 from 10 to 12 sites in New Jersey (USA); with each site having wild and cultivated blueberries growing in close proximity. The preference and performance of D. suzukii on wild and cultivated blueberries were studied in choice and no-choice bioassays. In addition, we compared size, firmness, acidity (pH), total soluble solids (°Brix), and nutrient, phenolic, and anthocyanin content between wild and cultivated berries. In choice and no-choice bioassays, more eggs were oviposited in, and more flies emerged from, cultivated than wild blueberries. Cultivated fruits were 2x bigger, 47% firmer, 14% less acidic, and had lower °Brix, phenolic, and anthocyanin amounts per mass than wild fruits. Levels of potassium and boron were higher in cultivated fruits, while calcium, magnesium, and copper were higher in wild fruits. These results show that domestication and/or agronomic practices have made blueberries more susceptible to D. suzukii, which was associated with several physico-chemical changes in fruits. Our study documents the positive effects of crop domestication/cultivation on an invasive insect pest.

Crop Domestication Alters Floral Reward Chemistry With Potential Consequences for Pollinator Health

Crop domestication can lead to weakened expression of plant defences, with repercussions for herbivore and pathogen susceptibility. However, little is known about how domestication alters traits that mediate other important ecological interactions in crops, such as pollination. Secondary metabolites, which underpin many defence responses in plants, also occur widely in nectar and pollen and influence plant-pollinator interactions. Thus, domestication may also affect secondary compounds in floral rewards, with potential consequences for pollinators. To test this hypothesis, we chemically analysed nectar and pollen from wild and cultivated plants of highbush blueberry (Vaccinium corymbosum L.), before conducting an artificial diet bioassay to examine pollinator-pathogen interactions. Our results indicated that domestication has significantly altered the chemical composition of V. corymbosum nectar and pollen, and reduced pollen chemical diversity in cultivated plants. Of 20 plant metabolites identified in floral rewards, 13 differed significantly between wild and cultivated plants, with a majority showing positive associations with wild compared to cultivated plants. These included the amino acid phenylalanine (4.5 times higher in wild nectar, 11 times higher in wild pollen), a known bee phagostimulant and essential nutrient; and the antimicrobial caffeic acid ester 4-O-caffeoylshikimic acid (two times higher in wild nectar). We assessed the possible biological relevance of variation in caffeic acid esters in bioassays, using the commercially available 3-O-caffeoylquinic acid. This compound reduced Bombus impatiens infection by a prominent gut pathogen (Crithidia) at concentrations that occurred in wild but not cultivated plants, suggesting that domestication may influence floral traits with consequences for bee health. Appreciable levels of genetic variation and heritability were found for most floral reward chemical traits, indicating good potential for selective breeding. Our study provides the first assessment of plant domestication effects on floral reward chemistry and its potential repercussions for pollinator health. Given the central importance of pollinators for agriculture, we discuss the need to extend such investigations to pollinator-dependent crops more generally and elaborate on future research directions to ascertain wider trends, consequences for pollinators, mechanisms, and breeding solutions.

Role of Plant Volatiles in Host Plant Recognition by Listronotus maculicollis (Coleoptera: Curculionidae)

The annual bluegrass weevil (ABW), Listronotus maculicollis Kirby, is an economically important pest of short cut turfgrass. Annual bluegrass, Poa annua L., is the most preferred and suitable host for ABW oviposition, larval survival and development. We investigated the involvement of grass volatiles in ABW host plant preference under laboratory and field conditions. First, ovipositional and feeding preferences of ABW adults were studied in a sensory deprivation experiment. Clear evidence of involvement of olfaction in host recognition by ABW was demonstrated. Poa annua was preferred for oviposition over three bentgrasses, Agrostis spp., but weevils with blocked antennae did not exhibit significant preferences. ABW behavioral responses to volatiles emitted by Agrostis spp. and P. annua were examined in Y-tube olfactometer assays. Poa annua was attractive to ABW females and preferred to Agrostis spp. cultivars in Y-tube assays. Headspace volatiles emitted by P. annua and four cultivars of Agrostis stolonifera L. and two each of A. capillaris L. and A. canina L. were extracted, identified and compared. No P. annua specific volatiles were found, but Agrostis spp. tended to have larger quantities of terpenoids than P. annua. (Z)-3-hexenyl acetate, phenyl ethyl alcohol and their combination were the most attractive compounds to ABW females in laboratory Y-tube assays. The combination of these compounds as a trap bait in field experiments attracted adults during the spring migration, but was ineffective once the adults were on the short-mown turfgrass. Hence, their usefulness for monitoring weevil populations needs further investigation.

Development of Sparganothis sulfureana (Lepidoptera: Tortricidae) on Cranberry Cultivars

Sparganothis fruitworm (Sparganothis sulfureana Clemens) (Lepidoptera: Tortricidae) is a serious pest of cranberry (Vaccinium macrocarpon Aiton), a native North American fruit cultivated in northern regions of the United States and southeastern Canada. This study assessed antibiosis in several cranberry cultivars commonly grown in Wisconsin. Five cultivars previously shown to host different levels of populations of S. sulfureana in commercial cranberry were assessed in this study to evaluate the performance of S. sulfureana amongst these cultivars. We measured growth and time to developmental stages of newly emerged larvae to adulthood on selected cranberry cultivars in the laboratory. There was no difference in the rates of survival to pupation and to adult emergence among any of the cultivars tested. Mid-instar larvae that fed on the cultivar 'Ben Lear' were heavier than those feeding on 'GH-1', 'Stevens', or 'HyRed', and larvae that fed on 'Mullica Queen' were heavier than those feeding on 'HyRed'. However, there were no significant differences in pupal weights or in the number of days from neonate to adult emergence among varieties. Therefore, this study did not provide evidence of antibiosis among the cultivars tested, and found that larval weight was not correlated with other measurements of performance.

Fine-tuning the 'plant domestication-reduced defense' hypothesis: specialist vs generalist herbivores

Domesticated plants are assumed to have weakened chemical defenses. We argue, however, that artificial selection will have maintained defense traits against specialized herbivores that have coexisted with the crops throughout their domestication. We assessed the performance of eight species of insect herbivores from three feeding guilds on six European maize lines and six populations of their wild ancestor, teosinte. A metabolomics approach was used in an attempt to identify compounds responsible for observed differences in insect performance. Insects consistently performed better on maize than on teosinte. As hypothesized, this difference was greater for generalist herbivores that are normally not found on teosinte. We also found clear differences in defense metabolites among the different genotypes, but none that consistently correlated with differences in performance. Concentrations of benzoxazinoids, the main chemical defense in maize, tended to be higher in leaves of teosinte, but the reverse was true for the roots. It appears that chemical defenses that target specialized insects are still present at higher concentrations in cultivated maize than compounds that are more effective against generalists. These weakened broad-spectrum defenses in crops may explain the successes of novel pests.

Root symbionts: Powerful drivers of plant above- and belowground indirect defenses

Soil microbial mutualists of plants, including mycorrhizal fungi, non-mycorrhizal fungi and plant growth promoting rhizobacteria, have been typically characterized for increasing nutrient acquisition and plant growth. More recently, soil microbes have also been shown to increase direct plant defense against above- and belowground herbivores. Plants, however, do not only rely on direct defenses when attacked, but they can also recruit pest antagonists such as predators and parasitoids, both above and belowground, mainly via the release of volatile organic compounds (i.e., indirect defenses). In this review, we illustrate the main features and effects of soil microbial mutualists of plants on plant indirect defenses and discuss possible applications within the framework of sustainable crop protection against root- and shoot-feeding arthropod pests. We indicate the main knowledge gaps and the future challenges to be addressed in the study and application of these multifaceted interactions.

Plant Flavonoid Content Modified by Domestication

Plant domestication can modify and weaken defensive chemical traits, reducing chemical defenses in plants and consequently their resistance against pests. We characterized and quantified the major defensive flavonols and isoflavonoids present in both wild and cultivated murtilla plants (Ugni molinae Turcz), established in a common garden. We examined their effects on the larvae of Chilesia rudis (Butler) (Lepidoptera: Arctiidae). Insect community and diversity indices were also evaluated. We hypothesized that domestication reduces flavonoid contents and modifies C. rudis preference, the insect community, and diversity. Methanolic extracts were obtained from leaves of U. molinae plants and analyzed by high performance liquid chromatography. Results showed higher insect numbers (86.48%) and damage index (1.72 ± 0.16) in cultivated plants. Four new first records of insects were found associated with U. molinae. Diversity indices, such as Simpson, Shannon, and Margalef, were higher in cultivated plants than in wild plants. Furthermore, eight isoflavonoids were identified in U. molinae leaves for the first time. The five flavonols showed higher concentrations in wild U. molinae leaves (89.8 µg/g) than in cultivated plants (75.2 µg/g); however, no differences were found in isoflavonoids between wild and cultivated plants. The larvae of C. rudis consumed more leaf material of cultivated plants than wild plants in choice (3.8 vs. 0.8 mm2) and no-choice (7.5 vs. 3.0 mm2) assays. Our study demonstrates that domestication in U. molinae reduces the amount of flavonoids in leaves, increasing the preference of C. rudis and the insect community.

Nocturnal herbivore-induced plant volatiles attract the generalist predatory earwig Doru luteipes Scudder

Numerous studies have demonstrated that entomophagous arthropods use herbivore-induced plant volatile (HIPV) blends to search for their prey or host. However, no study has yet focused on the response of nocturnal predators to volatile blends emitted by prey damaged plants. We investigated the olfactory behavioral responses of the night-active generalist predatory earwig Doru luteipes Scudder (Dermaptera: Forficulidae) to diurnal and nocturnal volatile blends emitted by maize plants (Zea mays) attacked by either a stem borer (Diatraea saccharalis) or a leaf-chewing caterpillar (Spodoptera frugiperda), both suitable lepidopteran prey. Additionally, we examined whether the earwig preferred odors emitted from short- or long-term damaged maize. We first determined the earwig diel foraging rhythm and confirmed that D. luteipes is a nocturnal predator. Olfactometer assays showed that during the day, although the earwigs were walking actively, they did not discriminate the volatiles of undamaged maize plants from those of herbivore damaged maize plants. In contrast, at night, earwigs preferred volatiles emitted by maize plants attacked by D. saccharalis or S. frugiperda over undamaged plants and short- over long-term damaged maize. Our GC-MS analysis revealed that short-term damaged nocturnal plant volatile blends were comprised mainly of fatty acid derivatives (i.e., green leaf volatiles), while the long-term damaged plant volatile blend contained mostly terpenoids. We also observed distinct volatile blend composition emitted by maize damaged by the different caterpillars. Our results showed that D. luteipes innately uses nocturnal herbivore-induced plant volatiles to search for prey. Moreover, the attraction of the earwig to short-term damaged plants is likely mediated by fatty acid derivatives.

Gypsy moth herbivory induced volatiles and reduced parasite attachment to cranberry hosts

Interactions between species can have cascading effects that shape subsequent interactions. For example, herbivory can induce plant defenses that affect subsequent interactions with herbivores, pathogens, mycorrhizae, and pollinators. Parasitic plants are present in most ecosystems, and play important roles in structuring communities. However, the effects of host herbivory on parasitic plants, and the potential mechanisms underlying such effects, are not well known. We conducted a greenhouse study to ask whether gypsy moth (Lymantria dispar) damage, host cultivar, and their interaction affected preference of the stem parasite dodder (Cuscuta spp.) on cranberry hosts (Vaccinium macrocarpum). We then assessed the mechanisms that could underlie such effects by measuring induced changes in phytohormones and secondary compounds. We found that damage by gypsy moths delayed dodder attachment by approximately 0.3 days when dodder stems were added 2 days after damage, and reduced attachment by more than 50% when dodder stems were added 1 week after host plant damage. Gypsy moth damage significantly increased jasmonic acid (JA) levels, total volatile emissions, and the flavonol, quercetin aglycone, suggesting possible mechanisms underlying variation in dodder ability to locate or attach to hosts. Dodder preference also differed between cranberry cultivars, with the highest attachment on the cultivar that had significantly lower levels of total volatile emissions and total phenolic acids, suggesting that volatile composition and phenolics may mediate dodder preference. Our results indicate that herbivory can reduce subsequent attachment by a highly damaging parasitic plant, demonstrating the potential importance of early damage for shaping subsequent species interactions.