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Belowground Insect Herbivory Induces Systemic Volatile Emissions That Strengthen Neighboring Plant Resistance Aboveground
Get PDFPlants transmit ecologically relevant messages to neighboring plants through chemical cues. For instance, insect herbivory triggers the production of herbivore-induced plant volatiles (HIPVs), which can enhance neighboring plant defenses. HIPVs are emitted from directly damaged plant tissues and from systemic, non-damaged tissues. Although volatile-mediated interplant interactions have been observed both above- and belowground, it remains unknown whether belowground herbivory induces systemic HIPVs aboveground that influence neighboring plants. To explore how belowground herbivory affects interplant interactions aboveground, we characterized systemic HIPVs from squash induced by belowground striped cucumber beetle (Acalymma vittatum) larval herbivory. We exposed squash ���receiver plants��� to systemic HIPVs or volatiles from non-damaged plants. We then measured herbivore resistance by challenging ���receiver plants��� with aboveground-feeding herbivores: adult beetles (A. vittatum) or squash bugs (Anasa tristis). We discovered belowground-damaged plants emitted more (E)-��-ocimene, a key volatile from the systemic HIPV blend, than non-damaged controls, and that exposure to systemic HIPVs enhanced neighboring plant resistance to aboveground squash bugs, but not adult beetles. Further investigations into the mechanism of interplant interaction revealed ��-ocimene alone can elicit plant resistance against squash bugs. Overall, our findings reveal a novel form of volatile-mediated interactions between plants spanning across aboveground-belowground plant systems
Olfactory Cues Mediate Multitrophic Interactions Among Cucumber Plants, Cucumber Beetle Larvae and Entomopathogenic Nematodes
Get PDFOlfactory cues mediate a wide variety of ecological interactions among organisms at different trophic levels. There is abundant evidence that these cues play critical roles for organisms foraging for resources and defending against potential attackers. Some of the best-studied examples include plants producing volatile organic compounds to defend themselves against herbivores and natural enemies using prey-associated odors while hunting. While much of this research has focused on aboveground systems, there is growing recognition that olfactory cues also facilitate multitrophic interactions among soil-dwelling organisms. The overall purpose of this thesis was to examine how olfactory cues from plants and natural enemies guide the foraging decisions of herbivores and their natural enemies, focusing on a belowground tritrophic system.
First, I review the literature to examine how plant-associated microorganisms alter plant phenotypes to influence herbivore foraging behavior. Next, I investigate the roles of herbivore-induced plant volatiles (HIPVs) from roots of cucumber plants (Cucumis sativus) as foraging cues for a specialist herbivore, striped cucumber beetle (Acalymma vittatum) and its natural enemies, entomopathogenic nematodes (EPNs, Heterorhabditis bacteriophora). I predicted HIPVs from A. vittatum���damaged roots would attract EPNs, while repelling conspecific larvae that avoid competition, and increased risk of predation by EPNs. Finally, I evaluated how olfactory cues emitted by 3 species of EPNs with differing foraging strategies affect the behavior of their insect herbivore prey (A. vittatum) and competing EPNs. I hypothesized olfactory cues from the more sedentary ���ambush��� EPN species (Steinernema carpocapsae) would be the most repulsive to prey and potential competitors, compared to cues from the active-hunting (H. bacteriophora) or intermediate-foraging (Steinernema riobrave) species.
In the second study, I found that 24 hours of wounding by A. vittatum herbivory, or mechanical damage, induced greater production of volatiles from C. sativus roots compared to undamaged controls, repelling foraging larvae and recruiting EPNs. However, after sustained herbivory for 7 days, larvae reduced HIPVs to levels indistinguishable from undamaged roots, while mechanically damaged roots continued to produce higher levels of volatiles. Attenuation of HIPVs impaired C. sativus indirect defenses by reducing recruitment of EPNs and deterrence of A. vittatum larvae.
In the final study, I found that foraging A. vittatum larvae avoided olfactory cues from the active-hunting EPN species, Heterorhabditis bacteriophora, but did not respond to cues from the ambush hunter, S. carpocapsae, or intermediate hunter, S. riobrave. In contrast, foraging H. bacteriophora EPNs were attracted to odors produced by the two Steinernema EPN species and did not respond to olfactory cues from conspecifics.
Taken together, these results suggest that A. vittatum larvae can navigate risk within the soil environment, first, by avoiding volatile cues associated with increased predation risk or competition ( i.e., volatiles from herbivore-damaged plants or odors from EPN-infected) and, second, through direct attenuation of plant indirect defenses. Our findings also indicate that active-hunting ���cruiser��� EPNs are attracted to multiple host-associated cues, including volatiles from herbivore-wounded C. sativus roots and odors from heterospefic EPN-infected insect cadavers, suggesting that these cues can provide information for foraging natural enemies about resource availability
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Understanding the Enemy: Genetics and Behavioral Ecology of Varroa destructor, the Parasitic Mite of the Western Honey Bee, Apis mellifera
No full textVarroa destructor is a cosmopolitan ectoparasitic mite that causes extensive detrimental effects on its new host Apis mellifera, The Western honey bee. Problems associated with Varroa parasitization include lower body weight, decreased learning capacity, lower stinging threshold, and shorter longevity. Varroa mites feed on the fat body tissue of developing and adult bees, and are also highly effective vectors of several honey bee-associated viruses, which can cause colony failure within a couple of years if no treatment is implemented. Beekeepers mainly rely on pesticides to lower the mite levels within colonies. However, most mite populations are now resistant to commonly used miticides, which is problematic because Varroa continues to wreak havoc on most beekeeping operations in the United States and around the world. The focus of this dissertation was to further understand the behavioral ecology of the Varroa mite, filling in the gaps in knowledge to better deal with this parasite. In the first research chapter, I found that honey bee worker larvae at closer proximity to drone brood did not have a higher risk of cell invasion by Varroa, but had a lower risk of cell invasion when they were on a frame with a high number of drone larvae. In the second research chapter, I did not find a clear link to between nurse visitation rates toward larval cells and an increased invasion of larval cells by Varroa. However, by experimentally increasing nurse visitation rates of worker brood after a 2-hr or 4-hr period of food restriction. I showed that precluding larvae from being fed for a given time period led to increased mite cell invasion later on. In the last research chapter, I measured the genetic diversity of Varroa mite populations across five states in the United States. I found clear differences in the genetic structure of mite populations between states and between apiaries. The results from this genetic study could be expanded further to understand whether certain genetically unique Varroa populations in the U.S. are more prone to being resistant to miticides, which could help us improve management methods to control this pervasive honey bee parasite
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Linking Plant Physiology and Chemical Communication: Herbivore-Associated Volatiles Modulate Photosynthesis and Plant Resistance to Herbivores
No full textPlant volatile communication plays a major role in plant defense against insects, yet we know little about the mechanisms of volatile perception and plant physiological responses (i.e., changes in photosynthetic rates and stomatal conductance) to volatile compounds.
In Chapter 2, I investigate the role of stomata in volatile perception by plants. My findings indicate that maize (Zea mays) plants take up and perceive specific volatile compounds through open stomata, which prime anti-herbivore defense responses. Furthermore, environmental conditions that modify stomatal aperture and/or defense signaling affect the ability of maize plants to perceive herbivore-induced plant volatiles (HIPVs) and prime their defenses.
In Chapters 3 and 4, I characterize the physiological responses of three crop plant species to herbivore-associated volatile compounds and assess insect and plant performance. In chapter 3, I experimentally determined that upon perception of HIPVs, maize (Zea mays) and cotton (Gossypium hirustum) plants reduce photosynthetic rates and stomatal conductance. Upon subsequent herbivory, plant photosynthetic performance remained lower, which may have contributed to observed differences in plant and insect performance. Because little is known about how plants physiologically respond to insect-derived volatiles, in chapter 4, I characterized the photosynthetic and stomatal responses of squash (Cucurbita pepo) plants to the aggregation pheromone of a specialist herbivore, the striped cucumber beetle (Acalymma vittatum). I found that squash plants responded to A. vittatum aggregation pheromone by strongly reducing photosynthetic rates and stomatal conductance. I also found that exposure to A. vittatum aggregation pheromone does not deter insect feeding as plants exposed to the pheromone had more leaf area removed and less aboveground biomass at the end of the experiment.
Together, these results suggest that basic plant physiological processes are a critical component of plant volatile communication. These findings document the role of stomatal pores and photosynthetic responses to volatile perception with broad significance for anti-herbivore defense responses
Understanding the Enemy: Genetics and Behavioral Ecology of Varroa destructor, the Parasitic Mite of the Western Honey Bee, Apis mellifera
No full textVarroa destructor is a cosmopolitan ectoparasitic mite that causes extensive detrimental effects on its new host Apis mellifera, The Western honey bee. Problems associated with Varroa parasitization include lower body weight, decreased learning capacity, lower stinging threshold, and shorter longevity. Varroa mites feed on the fat body tissue of developing and adult bees, and are also highly effective vectors of several honey bee-associated viruses, which can cause colony failure within a couple of years if no treatment is implemented. Beekeepers mainly rely on pesticides to lower the mite levels within colonies. However, most mite populations are now resistant to commonly used miticides, which is problematic because Varroa continues to wreak havoc on most beekeeping operations in the United States and around the world. The focus of this dissertation was to further understand the behavioral ecology of the Varroa mite, filling in the gaps in knowledge to better deal with this parasite. In the first research chapter, I found that honey bee worker larvae at closer proximity to drone brood did not have a higher risk of cell invasion by Varroa, but had a lower risk of cell invasion when they were on a frame with a high number of drone larvae. In the second research chapter, I did not find a clear link to between nurse visitation rates toward larval cells and an increased invasion of larval cells by Varroa. However, by experimentally increasing nurse visitation rates of worker brood after a 2-hr or 4-hr period of food restriction. I showed that precluding larvae from being fed for a given time period led to increased mite cell invasion later on. In the last research chapter, I measured the genetic diversity of Varroa mite populations across five states in the United States. I found clear differences in the genetic structure of mite populations between states and between apiaries. The results from this genetic study could be expanded further to understand whether certain genetically unique Varroa populations in the U.S. are more prone to being resistant to miticides, which could help us improve management methods to control this pervasive honey bee parasite
Understanding the Enemy: Genetics and Behavioral Ecology of Varroa destructor, the Parasitic Mite of the Western Honey Bee, Apis mellifera
No full textVarroa destructor is a cosmopolitan ectoparasitic mite that causes extensive detrimental effects on its new host Apis mellifera, The Western honey bee. Problems associated with Varroa parasitization include lower body weight, decreased learning capacity, lower stinging threshold, and shorter longevity. Varroa mites feed on the fat body tissue of developing and adult bees, and are also highly effective vectors of several honey bee-associated viruses, which can cause colony failure within a couple of years if no treatment is implemented. Beekeepers mainly rely on pesticides to lower the mite levels within colonies. However, most mite populations are now resistant to commonly used miticides, which is problematic because Varroa continues to wreak havoc on most beekeeping operations in the United States and around the world. The focus of this dissertation was to further understand the behavioral ecology of the Varroa mite, filling in the gaps in knowledge to better deal with this parasite. In the first research chapter, I found that honey bee worker larvae at closer proximity to drone brood did not have a higher risk of cell invasion by Varroa, but had a lower risk of cell invasion when they were on a frame with a high number of drone larvae. In the second research chapter, I did not find a clear link to between nurse visitation rates toward larval cells and an increased invasion of larval cells by Varroa. However, by experimentally increasing nurse visitation rates of worker brood after a 2-hr or 4-hr period of food restriction. I showed that precluding larvae from being fed for a given time period led to increased mite cell invasion later on. In the last research chapter, I measured the genetic diversity of Varroa mite populations across five states in the United States. I found clear differences in the genetic structure of mite populations between states and between apiaries. The results from this genetic study could be expanded further to understand whether certain genetically unique Varroa populations in the U.S. are more prone to being resistant to miticides, which could help us improve management methods to control this pervasive honey bee parasite
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