Entomology Theses and Dissertations

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AGRICULTURAL DRAINAGE DITCHES AS SOURCES OF BENEFICIAL SPIDERS TO ENHANCE CONSERVATION BIOCONTROL IN ADJACENT CROPLANDS
(2020) Kutz, Dylan James; Lamp, William O.; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Agricultural drainage ditches are uncropped areas on farms located above high-water tables to assist in the hydrologic control of croplands. Drainage ditches have increasingly become the subject of research as sources of beneficial arthropods for agroecosystems. Spiders, the most common generalist predator in most field crops, are an important component of conservation biocontrol, but little is known of spider assemblages in drainage ditches or the extent they colonize adjacent croplands from these ditches. To better understand the composition and population dynamics of spider assemblages in drainage ditches, my objectives were (1) to assess the structure of spider assemblages inhabiting drainage ditches in Maryland and (2) to determine how spider assemblages in drainage ditches and adjacent soybean fields change throughout the soybean growth cycle. Overall, my work contributes to understanding how valuable drainage ditches are as habitats for natural enemies like spiders and how ditches influence spider assemblages in adjacent croplands.
DEVELOPING A PERRENIAL LIVING MULCH SYSTEM FOR MANAGING PESTS AND AUGMENTING NATURAL BIOCONTROL IN MARYLAND CANTALOUPE SYSTEMS
(2022) Nunez, Demian Antonio; Hooks, Cerruti RR; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This study investigated how alsike clover (Trifolium hybridum) and Virginia wildrye (Elymus virginicus), when interplanted as a living mulch with cantaloupe, (Cucumis melo var. cantalupensis) would impact herbivorous and beneficial arthropod numbers. An additional objective was to determine how these living mulches would impact fruit yield and quality. It was hypothesized that there would be a reduction of cantaloupe pest herbivores and increase in natural enemy abundances in the interplanting compared to monoculture cantaloupe system. Some arthropods conformed to these expectations. However, most had a neutral or inconsistent response to the living mulches. Striped cucumber beetles (Acalymma vitattum), a major pest, were unaffected by the living mulches on most sampling dates. During several periods in both study years, leaf piercing herbivores including aphids were found in greater numbers on cantaloupe interplanted with clover than wildrye and/or monoculture. Spiders were found in greater abundance in cantaloupe interplanted with clover than wildrye or monoculture plantings during several sampling periods. Other natural enemy guilds such as parasitic wasps and piercing predators were inconsistently influenced by living mulch types. Yield was highest in the monoculture plots and living mulch was correlated with changes in fruit texture and color.
The Effect of Barley Cover Crop Residue and Herbicide Management on the Arthropod Community in No-Till Soybeans
(2016) Rosario-Lebron, Armando; Hooks, Cerruti RR; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Cover cropping has long been used as a method of reducing soil erosion, increasing soil quality and suppressing weeds. However, effects of cover crops in local farming systems are varied and can be affected by timing and method of cover crop termination. We conducted two field studies each in Upper Marlboro and Beltsville, Maryland between 2013 and 2014. The study consisted of three cover crop and one Fallow(F) treatments. Cover crop treatments were Early-Kill (EK) and Late-Kill in which the cover crop was killed with a post-emergent herbicide in late April and May, respectively; and flail mow (FM), in which a flail mower was used to terminate the cover crop in late May. In 2013 and 2014, plant sucking insects were consistently more numerous in EK than LK treatment. Our findings suggest chemical and mechanical termination on cover crops produce similar results on arthropod populations.
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.
ENHANCING BIOLOGICAL CONTROL BY GROUND BEETLES (COLEOPTERA: CARABIDAE) THROUGH AGRICULTURAL DRAINAGE DITCH MANAGEMENT PRACTICES
(2024) Shokoohi, Alireza; Lamp, William; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The establishment of semi-natural habitats on crop field margins is an increasingly popular integrated pest management (IPM) tool for conservation biological control of crop pests, decreasing reliance on harmful chemical pesticides. Agricultural drainage ditches are uncropped areas built to mitigate flooding on farms, but they may also provide suitable habitats for beneficial arthropods such as ground beetles, which are generalist predators of many common plant and invertebrate pests. In this study, I aimed to evaluate the potential of drainage ditches as natural habitats that promote biological control by ground beetles. To do this, my objectives were (1) to assess the impact of altered ditch management practices on ground beetle communities within a ditch and (2) to investigate ground beetle community composition and dynamics between ditch and adjacent crop field habitats across the Delmarva peninsula. Addition of straw to ditch banks in the fall increased ground beetle numbers by 97% in subsequent years, and ground beetle activity-density in drainage ditches was proportional to activity-density in adjacent fields for most genera. Results of this study suggest that altering drainage ditch management practices may provide additional ecological benefits by enhancing populations of ground beetles, thus reducing pest damage in adjacent crop fields.
Evaluating the potential benefits and long-term sustainability of neonicotinoid seed treatments in mid-Atlantic grain crop production
(2020) Dubey, Aditi; Hamby, Kelly A; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Neonicotinoid insecticide seed treatments (NSTs) are heavily used in US grain production; nearly all corn and over a third of soybeans grown are treated. However, NSTs primarily provide protection against occasional early-season soil and seedling pests and rarely improve yield. Additionally, the active ingredients from NSTs can spread and persist in the environment where they can impact various non-target organisms including beneficial arthropods and soil microorganisms. To determine the costs and benefits of NSTs in Maryland grain crops, I evaluated the impacts of two popular NSTs, imidacloprid and thiamethoxam, and their associated seed applied fungicides on insect pest suppression, yield, non-target arthropods, and soil health in a three-year rotation of full-season soybean, winter wheat, double-cropped soybean, and corn. Pest pressure was low throughout the study, as is typical for Maryland, and the NSTs did not provide any yield benefits. Treatments variably impacted non-target arthropods, reducing the abundance of some predators and parasitoids. Seed applied fungicides also impacted non-target arthropods. Because parasitoid wasps were disrupted in winter wheat up to 32 weeks after planting, I conducted a laboratory study to better understand NST suppression of cereal aphids and the mechanisms by which they affect cereal aphid parasitoids. Neonicotinoid seed treatments may not be effective enough to maintain aphids below the economic threshold in winter wheat; thus, they may negatively impact parasitoids through contaminated hosts. In my study, NSTs did not detectably affect soil health or the soil microbial community; however, they have the potential to harm aquatic communities through leaching and runoff. Given the lack of pest pressure and yield benefits, as well as the potential for non-target impacts, my research suggests that the use of NSTs in Maryland grain crops is neither warranted nor sustainable. It also highlights the need for further evaluation of the non-target impacts of seed applied fungicides, and of the effects of NSTs on water bodies within the Chesapeake Bay watershed.
Evaluating the Potential Benefits and Sustainability of a Novel Living and Dead Cover Crop Mixture in Mid-Atlantic Crop Production
(2023) Johnson, Veronica; Hooks, Cerruti RR; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Modern vegetable production systems are often characterized by monoculture fields andthe intensive use of tillage and/or synthetic agrochemicals for managing weeds and insect pests. A growing public interest in more sustainable and eco-friendly production practices has resulted in increased demand that crops be produced with lower inputs. Incorporating flowering living mulches and cover crop residues within crop fields can create an environment more hospitable to beneficial organisms and less conducive to pest outbreaks. My dissertation research aims to advance our knowledge in this area by evaluating the impacts of a novel cover cropping tactic which involves combining a perennial flowering living mulch with cover crop residue on insects and/or weeds. Further, it is often suggested that weed management requires a holistic approach; and that cover cropping will not be successful as a sole weed management tactic. As such, another research aim is to investigate whether combining a cover cropping tactic with herbicide sprays would result in better weed suppression and increased yield in sweet corn compared to using cover crops alone. An economic assessment was also performed to further evaluate the practicality of sweet corn producers adopting the management practices being investigated. Cost of seeds, labor and other expenses can be a primary limitation to cover crop usage. To this point, I also evaluated the feasibility of using a single cover crop planting to suppress weeds over multiple cropping systems and field seasons. If a single cover crop planting can be used over multiple seasons, this could reduce the cost of cover crop use. Agricultural intensification and conversion of natural landscapes to crop production fields have contributed to declines in insect biodiversity including natural enemies and pollinators. Advancing our understanding of how increasing vegetational diversity within crop fields influences weed pressure and populations of herbivores and beneficial arthropods, as well as production costs, can facilitate the adoption of practices in annual cropping systems that favor beneficial organisms and conserves insect biodiversity.
INFLUENCE OF A NATIVE INSECTARY PLANT, CHAMAECRISTA FASCICULATA (MICHX.) ON ORGANIC FIELD CORN AND ARTHROPOD COMMUNITIES
(2016) Hunt, Lauren; Hooks, Cerruti R.R.; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Increasing plant diversity in conventionally monoculture agrosystems has been promoted as a method to enhance beneficial arthropod density and efficacy, suppress herbivory and provide a range of ecosystem services. I investigated the pest suppressive potential and economic impact of plant diversification in organic field corn. The experiment consisted of two treatments, corn grown in monoculture (C) and bordered by strips of partridge pea (PP). Pest and natural enemy populations, corn damage, yield, and profits were compared among treatments. Natural enemy and herbivore arthropod populations were affected by treatment and distance from plot border. Corn damage due to pests was also affected by treatment and location, but did not significantly affect yield. Yield in monoculture plots was generally greater than in PP but did not result in greater profit. Pest and natural enemy arthropod abundances were elevated in partridge pea treatment borders, but these populations did not consistently diffuse into plot interiors. The potential causes and implications of findings are discussed.
ODONATA SPECIES COMPOSITION IN AGROECOSYSTEMS: PRELIMINARY SURVEYS WITH AN EMPHASIS ON POTENTIAL FOR BIOLOGICAL CONTROL ON FARMS
(2024) Hartman, Margaret Elizabeth; Lamp, William O; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Adult dragonflies and damselflies are efficient aerial predators that provide ecosystem service as consumers of pest arthropods. However, their role as predators of agricultural pests in agroecosystems has been understudied. The prey of odonates has been historically difficult to quantify but new molecular methods can make diet analysis easier. I conducted visual encounter surveys across four farms in 2020 and 2021. I found odonates were present on all farms surveyed but there were significant differences in abundance and richness. Fecal pellets were collected from 94 odonates in 2021 for prey DNA analysis using next generation sequencing. Nine odonate samples produced exceptional libraries, resulting in a large quantity of identifiable prey sequences. This preliminary study can help future researchers develop best practices for maintaining healthy farm water bodies and optimizing fecal DNA analysis methodology to better understand odonates’ potential for agricultural pest suppression.
POLLEN NUTRITION, PESTICIDES, AND PATHOGENS: INTERACTIVE EFFECTS ON HONEY BEE HEALTH
(2017) Garavito, Andrew; vanEngelsdorp, Dennis; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
While a variety of stressors influence honey bee (Apis mellifera) health, it is the additive and interactive effects of these factors on bee health that have been driving modern research. We devised a set of two experiments to test the effects of multiple stressors on honey bee health. First, we grew sunflowers to test the effects of drought stress and seed treatment on sunflower pollen. We fed the pollen collected from these sunflowers to cohorts of bees that were either infected or uninfected with the microsporidian pathogen Nosema ceranae to find that drought stressed pollen leads to increased mortality in infected bees. Next, we fed 37 experimental pollen diets of different floral varieties and pesticide loads to honey bees infected with N. ceranae, but we were unable to find a connection between diet variety and pesticide exposure on bee health.
Spatial heterogeneity of stink bug (Hemiptera: Pentatomidae) populations in agricultural systems
(2014) Venugopal, Dilip; Lamp, William O; Dively, Galen P; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Knowledge on spatial patterns of insect pest populations and the ecological processes influencing these patterns can be directly applied to the management of pests in agricultural systems. Recent increases in stink bug populations, importantly the invasive Halyomorpha halys (Stål 1855), has caused unprecedented economic losses in the mid-Atlantic United States. To inform integrated pest management programs, I quantified the spatial heterogeneity of stink bug population density in field crops at multiple spatial scales (field edge, entire fields and regional), and identified the associated environmental factors and the underlying ecological mechanisms (i.e. climatic tolerances, resource quality and availability). At corn and soybean field edges, highest density of stink bugs was limited to the first few crop rows. At some study sites, fields adjacent to woods and buildings harbored higher density of stink bugs than those adjacent to open areas. Injury to corn kernel damage, and soybean pod and seed increased with stink bug density, and was highest at the field edges. Stink bug density was also positively associated with yield loss in soybean. In entire fields of corn-soybean, H. halys was found in very low density or absent beyond 25m from the field edge. At study sites with high stink bug populations, interpolated density values showed potential dispersal of H. halys, particularly adults and large nymphs, from corn into soybean, coinciding with the end of dough stage in corn and beginning of soybean seed development stage. Temperature and developed areas, and proportion of forest and crop areas were important predictors of regional patterns in H. halys and Chinavis hilaris abundance, respectively. For Euschistus servus, temperature and forest cover influenced patterns at broad spatial scale. Adjacent habitat influence, with highest abundance along woods, on stink bug density was limited to within field scale, and difference in abundance between sites was driven primarily by temperature gradient. These results directly inform field level stink bug management strategies through planting date and orientation of fields in the landscape, and for timing and intensity of treatments, as well as area-wide management. This research also identified roles of temperature and landscape in facilitating or impeding invasive pest populations.
UNDERSTANDING THE RELATIONSHIP BETWEEN THE BROWN MARMORATED STINK BUG, HALYOMORPHA HALYS (STÅL), AND ITS SYMBIONT, PANTOEA CARBEKII, WITH IMPLICATIONS FOR STINK BUG MANAGEMENT
(2016) Taylor, Christopher Michael; Mitter, Charles; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Symbiotic relationships between insects and beneficial microbes are very common in nature, especially within the Hemiptera. The brown marmorated stink bug, Halyomorpha halys Stål, harbors a symbiont, Pantoea carbekii, within the fourth region of the midgut in specialized crypts. In this dissertation, I explored this insect- microbe relationship. I determined that the brown marmorated stink bug is heavily reliant on its symbiont, and that experimental removal of the symbiont from the egg mass surface prior to nymphal acquisition led to lower survival, longer development, lower fecundity, and aberrant nymphal behavior. Additionally, I determined that even when the symbiont is acquired and housed in the midgut crypts, it is susceptible to stressors. Stink bugs reared at a higher temperature showed lower survival, longer development, and a cease in egg mass production, and when bugs were screened for their symbiont, fewer had successfully retained it while under heat stress. Finally, with the knowledge that the stink bug suffers decreases in fitness when its symbiont is missing or stressed, I wanted to determine if targeting the symbiont was a possible management technique for the stink bug. I tested the efficacy of a number of different insecticidal and antimicrobial products to determine whether prevention of symbiont acquisition from the egg mass was possible, and results indicated that transmission of the symbiont from the egg mass to the newly hatched nymph was negatively impacted when certain products were applied (namely surfactants or products containing surfactants). Additionally, direct effects on hatch rate and survival were reported for certain products, namely the insect growth regulator azadirachtin, which suggests that nymphs can pick up residues from the egg mass surface while probing for the symbiont. I conclude that P. carbekii plays a critically important role in the survival of its host, the brown marmorated stink bug, and its presence on the egg mass surface before nymphal hatch makes it targetable as a potential management technique.
USING A LIVING MULCH AND WOLF SPIDERS TO MANAGE PEST ARTHROPODS IN CUCUMBER
(2017) Kahl, Hanna Maria; Hooks, Cerruti; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Pest management practices that conserve beneficial organisms and improve yield are needed. This research aims to determine how: 1) red clover living mulch impacts insect herbivores, arthropod natural enemies, and cucumber quality and yield, and 2) wolf spiders influence cucumber beetles and cucumber plant attributes. Herbivore and natural enemy abundances on cucumber plants in plots with and without interplanted red clover (RC) were compared using foliage searches and sticky cards. Effects of spiders on cucumber beetle behavior, densities, and mortality was assessed in cages with and without a wolf spider and/or their cues. RC plots had fewer striped cucumber beetles and aphids, and more big-eyed bugs and minute pirate bugs. Spotted cucumber beetle densities were reduced and striped cucumber beetle mortality was higher in cages with than without spiders. These studies demonstrated that red clover living mulch and wolf spiders can be used to decrease pest arthropods in cucumber.

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