Entomology
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Item Unraveling Metarhizium interactions with insects, plants and microbes(2019) Lovett, Brian; St. Leger, Raymond J; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Metarhizium fungi have dual lifestyles as insect pathogens and as rhizospheric plant symbionts. Since these fungi can vary widely in their virulence and host-specificity, they provide a powerful model for host-pathogen interactions. Today, it is clear the greatest potential of these fungi lies in their application as transgenic biotechnologies. Biotechnologies are rightly subjected to increased scrutiny, and this dissertation seeks to assess the risks and benefits of applying transgenic Metarhizium fungi using bioinformatics. After sequencing the early-diverged generalist Metarhizium frigidum, comparative genomics has upended our understanding of the trajectory of Metarhizium evolution. Using a functional gene microarray, I assessed the impacts these fungi have on the soil microbial community, establishing a protocol for evaluating possible risks of applying transgenic entomopathogenic fungi. To inform the evaluation and development of next-generation transgenic Metarhizium strains in the future, I evaluated the specific mosquito immune response to Metarhizium pingshaense during early infection with and without Plasmodium falciparum (the human malaria parasite) using transcriptomics. A strain of this fungus engineered to express a potent arthropod-derived, insect-specific neurotoxin in mosquito hemolymph, was also evaluated for mosquito control efficacy in semi-field trials in West Africa. Together, this body of work offers a comprehensive view of the evolution of this fungal genus and how transgenic fungi interact with insects, plants and microbes. The results herein comprise a framework for evaluating the risks and efficacy of transgenic fungi.Item Home sick: impacts of migratory beekeeping on honey bee (Apis mellifera) pests, pathogens, and colony size(PeerJ, 2018-11-02) Alger, Samantha A.; Burnham, P. Alexander; Lamas, Zachary S.; Brody, Alison K.; Richardson, Leif L.Honey bees are important pollinators of agricultural crops and the dramatic losses of honey bee colonies have risen to a level of international concern. Potential contributors to such losses include pesticide exposure, lack of floral resources and parasites and pathogens. The damaging effects of all of these may be exacerbated by apicultural practices. To meet the pollination demand of US crops, bees are transported to areas of high pollination demand throughout the year. Compared to stationary colonies, risk of parasitism and infectious disease may be greater for migratory bees than those that remain in a single location, although this has not been experimentally established. Here, we conducted a manipulative experiment to test whether viral pathogen and parasite loads increase as a result of colonies being transported for pollination of a major US crop, California almonds. We also tested if they subsequently transmit those diseases to stationary colonies upon return to their home apiaries. Colonies started with equivalent numbers of bees, however migratory colonies returned with fewer bees compared to stationary colonies and this difference remained one month later. Migratory colonies returned with higher black queen cell virus loads than stationary colonies, but loads were similar between groups one month later. Colonies exposed to migratory bees experienced a greater increase of deformed wing virus prevalence and load compared to the isolated group. The three groups had similar infestations of Varroa mites upon return of the migratory colonies. However, one month later, mite loads in migratory colonies were significantly lower compared to the other groups, possibly because of lower number of host bees. Our study demonstrates that migratory pollination practices has varying health effects for honey bee colonies. Further research is necessary to clarify how migratory pollination practices influence the disease dynamics of honey bee diseases we describe here.Item Diversity and structure of Metrosideros polymorpha canopy arthropod communities across space and time(2019) Tielens, Elske Karolien; Gruner, Daniel S; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Global biodiversity is under pressure from climate change, habitat fragmentation and other anthropogenic change, and our ability to predict biodiversity responses to change requires a better understanding of the processes that drive diversity and structure local communities. However, quantifying these processes has proven to be challenging for multiple reasons; diversity is multidimensional, and both diversity and the processes that generate it vary across scale. In this dissertation, I examine temporal and spatial patterns in community structure to test hypotheses about the drivers of local diversity and composition in communities of varying age, focusing on arthropod communities associated with the native tree Metrosideros polymorpha on the Hawaiian Islands. Analysis of Hemiptera (true bug) communities reveals a temporal pattern in community structure, where young substrate communities were variable in species composition and beta dispersion decreased with substrate age, indicating convergence. However, substrate age did not correlate with community dissimilarity in a directional way. Similarly, geographic distance did not correlate with compositional dissimilarity, suggesting a lack of dispersal limitation. I confirmed this result by examining connections between arthropod communities in a historically fragmented ‘kīpuka’ landscape, using species-area relationships and graph theory analyses. Finally, if canopy arthropods are dispersive and differences in species composition across sites are not driven by substrate age, local habitat characteristics may influence species composition. I determined the role of local beta diversity and identified habitat characteristics regarding forest structure and host leaf traits that are strong drivers of beta diversity and species composition. Then, to further explore local habitat drivers I examined forests with high intraspecific variation in co-occurring Metrosideros. In this hybrid zone, insect life history traits shape species’ response to intraspecific variation in host plant characteristics, highlighting the importance of including dimensions of biodiversity beyond taxonomic diversity. Together, these results demonstrate the importance of local habitat conditions for canopy arthropods, suggest that canopy arthropod communities are highly connected and that substrate age plays a limited role in determining local arthropod communities. Such insights into biodiversity and plant-insect interactions across temporal and spatial scale are integral to understanding and conserving our natural world.Item Effect Of Nrf2 Inducers On Honey Bee Gene Expression And Pesticide-Related Mortality(2019) Brandt, Elizabeth A.; Hawthorne, David; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Honey bees are vitally important as pollinators to ecosystems and agricultural economy, yet they are threatened by the presence of pesticides and the wide array of xenobiotics they encounter while foraging. To better understand their metabolic detoxification of these compounds, it is important to elucidate the gene expression pathways involved in their response to toxin exposure. I investigated the potential detoxification role in honey bees of the Nrf2/Keap1 regulatory pathway, one of the most well-researched cellular toxin response mechanisms in vertebrates. I analyzed the effect of inducers on the toxicity of three different pesticides when exposed to bees, and the effects of Sulforaphane on select detoxification gene expression. Inducer consumption effects on pesticide toxicity ranged from synergistic to abrogative depending on the pesticide tested. PCR analysis of gene expression did not reveal significant effects of inducer consumption on expression of detoxification genes. This study and its results lay important groundwork for future research of this regulatory pathway in honey bees.Item EVALUATING THE EFFECT OF POTATO LEAFHOPPER (EMPOASCA FABAE) FEEDING ON BIOLOGICAL NITROGEN FIXATION IN ALFALFA (MEDICAGO SATIVA)(2019) Thompson, Morgan; Lamp, William O; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aboveground feeding by potato leafhopper (PLH), Empoasca fabae, (Hemiptera: Cicadellidae) causes significant injury to alfalfa (Medicago sativa), including disrupting translocation of fixed carbon from leaves to roots. Basal transport of fixed carbon in alfalfa fuels a critical mutualism between roots and nitrogen-fixing bacteria (Sinorhizobium meliloti). Above- and belowground nutrient allocation in alfalfa determines perennial persistence across growing seasons, as well as forage quality. Whether leafhopper feeding alters nutrient allocation and subsequently affects nitrogen fixation, however, is not clear. To test this, my objectives were 1) to examine the effect of different management strategies on PLH injury and nitrogen fixation, and 2) to quantify the amount and location of fixed nitrogen in whole alfalfa plants when fed on by leafhoppers. Overall, my work contributes to an understanding of how aboveground pest pressure can disrupt belowground processes in plants and ultimately affect the economic viability of crops for growers.Item Can Cover Crop Residues Suppress Pests and Improve Yield in Eggplant?(2018) Coffey, Peter Lawson; Hooks, Cerruti RR; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Field studies were conducted over three growing seasons to investigate the effects of planting eggplant following three winter cover crop treatments on the abundance, predation, and colonization of Colorado potato beetle (Leptinotarsa decemlineata) and flea beetle (Epitrix spp.) abundance. Colorado potato beetle densities were observed to be significantly higher in the early season, and lower in the mid- and late- season when eggplant was planted into a crimson clover residue, compared with a crimson clover – rye mixture or bare ground control. Flea beetle abundance was significantly higher in treatments planted with a winter cover crop. Seedbed preparation treatments for weed control did not significantly affect pest abundance. These results contrast with previous research, raising new questions about how cover crop mixtures interact with pests, and how suppression methods influence the effects cover crops have on arthropod populations.Item SPATIAL DISTRIBUTION, HABITAT PREFERENCE, AND SOCIETAL IMPACT OF THE NUISANCE BLACK FLY, SIMULIUM JENNINGSI(2018) Wilson, Rebecca Cathleen; Lamp, William; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Black flies (Diptera: Simuliidae) can cause pest problems through the females’ blood-seeking behavior. Nuisance black flies are managed through area-wide pest management at the larval stage, which necessitates tracking the distribution of both life stages. The species Simulium jenningsi is a nuisance pest in the mid-Atlantic United States. In Washington County, Maryland, residents began campaigning for state management of S. jenningsi in 2013. In my dissertation I used the localized nature of the S. jenningsi nuisance in western Maryland to investigate the environmental correlates to S. jenningsi abundance patterns and how this pest impacts the lives of residents. Survey responses regarding the annoyance and impact of black flies on resident quality of life were used to assess the societal component of S. jenningsi nuisance. Online respondents, those with children, and those who had lived in the region for a shorter amount of time were more likely to report black flies as “extremely annoying.” Quality of life concerns stemmed from avoidance of exercise and dissatisfaction with preventative strategies. The results contextualized the needs of residents in future management and topics for outreach efforts. Distribution patterns of the host-seeking females were studied within a 2000 km2 area centered on Washington County. High counts of flies were clustered in southern Washington County, although S. jenningsi could be found throughout the sampling area. Regression analysis showed relationships between higher adult fly abundance and environmental factors, including higher elevation, less surrounding impervious surface, and closer proximity to productive larval habitat. The factors associated with immature S. jenningsi abundance were studied at eight sites spanning the Potomac and Shenandoah Rivers. Simulium luggeri, a related species not identified as a pest in Maryland, was also found at each location. S. jenningsi was associated with higher flow velocity and temperature, while S. luggeri was associated with higher seston chlorophyll a content. Both species were associated with higher surrounding tree canopy, implying a possible connection to oviposition cues. Results from this dissertation suggest factors associated with optimal monitoring locations for adult S. jenningsi and indicate management should focus on areas of high flow velocity for larval populations.Item FOREST MICRO-HYMENOPTERA, INCLUDING THOSE ATTACKING TREES (CYNIPIDAE OAK GALL WASPS) AND THOSE POTENTIALLY DEFENDING THEM (PARASITIC PTEROMALIDAE)(2018) Cooke, Crystal; Miter, Charles; Gates, Michael; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The first part of this dissertation details studies involving an important group of insects attacking oaks, the oak gall wasps (Cynipidae: Cynipini). The second part deals with pteromalid parasitoids involved in thousand cankers disease affecting walnuts. Oak gall wasps are parasites that mainly attack oaks and induce highly differentiated plant growths, called galls, in which they develop. Most gall wasps alternate between dimorphic asexual and sexual generations. However, most species are only known from one generation with the other remaining undescribed. The taxonomy across much of Cynipini is in need of revision. Ultraconserved elements are used to collect phylogenomic data (average 956loci per specimen) for the oak gall wasps. Numerous genera were found to be polyphyletic with separate Nearctic and Palearctic lineages. The ancestor to Cynipini is thought to have been Palearctic based on the taxa sampled. One of the genera found to be polyphyletic, Disholcaspis Dalla Torre and Kieffer, is being thoroughly evaluated in preparation for revision. These efforts include the discovery and identification of new sexual generations, discovery of a new species, locating type specimens, and imaging of species in the genus. The molecular tools used for the identification of sexual generations exposed a great need for more loci, lending support for why phylogenomics is a valid option for this group. Thousand cankers disease is threatening cultivated and natural walnut tree populations. The disease is caused by a phytopathenogenic fungus, Geosmithia morbida Kolařík , Freeland, Utley, and Tisserat, that is vectored by the walnut twig beetle, Pityophthorus juglandis Blackman. Studies that have reared insects from trees infected with thousand cankers disease have resulted in the discovery of two new species of parasitoid wasps in the subfamily Cerocephalinae (Pteromalidae). The first was Theocolax americanus McEwen which was found in Colorado, USA though the natural origin and host are unknown. The second was Cerocephala flavus Cooke-McEwen which was found in the Piemonte region of Italy though its natural origin is also unknown. Cerocephaline wasps are known to attack wood boring beetles so these parasitoid wasps are thought to be associated with P. juglandis.Item Effects of post-harvest management practices on the degradation of Bacillus thuringiensis proteins in genetically modified corn residue(2018) Johnson, Veronica; Hooks, Cerruti RR; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Most studies addressing the ecological effects of Bt crops have focused on non-target effects during the crop growing cycle. Less information is available on the fate of expressed toxins in crop residue after harvest in a no-till production system. This research investigated the effects of four post-harvest management practices on the degradation rates of Cry proteins expressed in SmartStax field corn. Cry protein degradation expressed as growth inhibition of Ostrinia nubilalis larvae after harvest was measured by a feeding bioassay, and enzyme-linked immunosorbent assays were used to detect the presence of Cry proteins. Cry proteins retained significant levels of biological activity at crop senescence and were still present in corn residue for more than 20 weeks after harvest. Despite inconsistencies in treatment effects, the study demonstrated that post-harvest practices that increase soil-residue contact increase protein degradation, thereby reducing the period of exposure for non-target organisms.Item HEMIPTERAN INSECTS AS MODELS FOR UNDERSTANDING SEGMENTATION(2018) Chen, Mengyao; Pick, Leslie; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although segmentation is highly conserved in arthropods, diverse mechanisms underlie segmentation. Pair-rule genes (PRGs) are a group of genes controlling segmentation in Drosophila melanogaster, a holometabolous insect. While Drosophila are long-germ insects, most insects add segments sequentially. Studying the role of PRGs in sequentially-segmenting species will provide a deeper understanding in terms of developmental biology. Here, I studied two such insects: Halyomorpha halys and Oncopeltus fasciatus, hemimetabolous insects in a sister order to Holometabola. I annotated segmentation genes in the Halyomorpha genome and tested its response to RNA interference which I showed to be effective in this species for the first time. I further showed that three orthologs of Drosophila PRGs are present in the Oncopeltus genome and are expressed during stages at which segments are specified. Surprisingly, only one of these orthologs is expressed in a PR-pattern, indicating that PRG expression and function have changed during insect evolution.