Entomology

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    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.
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    INDIGENOUS NATURAL ENEMIES OF THE INVASIVE BROWN MARMORATED STINK BUG, HALYOMORPHA HALYS (HEMIPTERA: PENTATOMIDAE)
    (2013) Jones, Ashley Lynn; Shrewsbury, Paula M; Hooks, Cerruti RR; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), is an invasive species native to Southeastern Asia. Since its arrival into the U.S., BMSB has become an economically important pest in many cropping systems, including woody ornamental plants. Here I have explored the potential impact of indigenous natural enemies on BMSB in woody ornamental nursery systems in Maryland. When sampling for indigenous natural enemies in 2012 and 2013, I found seven species of egg parasitoids attacking BMSB with especially high parasitism rates from Anastatus reduvii. Overall egg mortality averaged 58% and parasitism rates increased from32% in 2012 to 44% in 2013. When sampling for predators as biological control agents, predation was low overall. I found that Arilus cristatus consumed more BMSB than any other predator species tested though low abundances were observed in the field. I also found that the use of sentinel egg masses may underestimate rates of parasitism.
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    Potential for entomopathogenic nematodes in biological control: a meta-analytical synthesis and insights from trophic cascade theory
    (2008) Denno, Robert; Gruner, Daniel; Kaplan, Ian
    Entomopathogenic nematodes (EPN) are ubiquitous and generalized consumers of insects in soil food webs, occurring widely in and agricultural ecosystems on all continents. Augmentative releases of EPN have been used to enhance biological control of pests in agroecosystems. Pest managers strive to achieve a trophic cascade whereby natural-enemy effects permeate down through the food web to suppress host herbivores and increase crop production. Although trophic cascades have been studied in diverse aboveground arthropod-based systems, they are infrequently investigated in soil systems. Moreover, no overall quantitative assessment of the effectiveness of EPN in suppressing hosts with cascading benefits to plants has been made. Toward synthesizing the available but limited information on EPN and their ability to suppress prey and affect plant yield, we surveyed the literature and performed a meta-analysis of 35 published studies. Our analysis found that effect sizes for arthropod hosts as a result of EPN addition were consistently negative and indirect effects on plants were consistently positive. Results held across several different host metrics (abundance, fecundity and survival) and across several measures of plant performance (biomass, growth, yield and survival). Moreover, the relationship between plant and host effect size was strikingly and significantly negative. That is, the positive impact on plant responses generally increased as the negative effect of EPN on hosts intensified, providing strong support for the mechanism of trophic cascades. We also review the ways in which EPN might interact antagonistically with each other and other predators and pathogens to adversely affect host suppression and dampen trophic cascades. We conclude that the food web implications of multiple-enemy interactions involving EPN are poorly studied, but, as management techniques that promote the long-term persistence of EPN are improved, antagonistic interactions are more likely to arise. We hope that the likely occurrence of antagonistic interactions in soil food webs should stimulate researchers to conduct field experiments explicitly designed to examine multiple-enemy interactions involving EPN and their cascading effects to hosts and plants.
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    Dynamics of a subterranean trophic cascade in space and time
    (2008) Ram, Karthik; Gruner, Daniel; McLaughlin, John; Preisser, Evan; Strong, Donald
    Trophic cascades, whereby predators indirectly benefit plant biomass by reducing herbivore pressure, form the mechanistic basis for classical biological control of pest insects. Entomopathogenic nematodes (EPN) are lethal to a variety of insect hosts with soil-dwelling stages, making them promising biocontrol agents. EPN biological control programs, however, typically fail because nematodes do not establish, persist and/or recycle over multiple host generations in the field. A variety of factors such as local abiotic conditions, host quantity and quality, and rates of movement affect the probability of persistence. Here, we review results from 13 years of study on the biology and ecology of an endemic population of Heterorhabditis marelatus (Rhabditida: Heterorhabditidae) in a California coastal prairie. In a highly seasonal abiotic environment with intrinsic variation in soils, vegetation structure, and host availability, natural populations of H. marelatus persisted at high incidence at some but not all sites within our study area. Through a set of field and lab experiments, we describe mechanisms and hypotheses to understand the persistence of H. marelatus. We suggest that further ecological study of naturally occurring EPN populations can yield significant insight to improve the practice and management of biological control of soil-dwelling insect pests.
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    Predator diversity, habitat complexity and the strength of terrestrial trophic cascades
    (2005-04-15) Finke, Deborah Lee; Denno, Robert F; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Food web complexity is thought to weaken the strength of terrestrial trophic cascades whereby strong natural enemy impacts on herbivores cascade to indirectly influence primary production. Predator diversity can enhance food web complexity by promoting the occurrence of intraguild predation, wherein predators feed on each other and on shared prey. In such cases, theory suggests that the impact of predation on herbivores relaxes and cascading effects on basal resources are dampened. In a terrestrial marsh community, I compared arthropod predator impacts on herbivores and plant productivity between a simple food web with a single predator species and a complex food web with a diverse predator assemblage. I found that enhancing predator diversity dampened enemy effects on herbivores and weakened trophic cascades. The role of intraguild predators in dampening such trophic cascades was determined by factorially manipulating predator species richness (1, 2, or 3 species) and predator trophic composition (strict predators, intraguild predators, or a mixture of both) and measuring their effects on prey suppression and plant productivity. I found that the impact of predator richness on the strength of trophic cascades was dependent on the trophic composition of the predator complex present. Specifically, strict predators additively enhanced planthopper suppression and increased plant productivity with an increase in species richness. However, intraguild predators interacted antagonistically, resulting in greater herbivore abundance and lower plant productivity at the highest levels of species richness. An investigation of the influence of habitat complexity on cascading predator effects revealed that complex habitats with cordgrass leaf litter provided a refuge for predators from intraguild predation and elevated planthopper suppression by the diverse predator assemblage. However, reducing the antagonistic predator-predator interactions and increasing prey suppression did not enhance the conductance of predator effects through the food web to impact positively primary producers, although there was a trend towards greater plant biomass in the complex-structured habitat. Therefore, the possibility exists that changes in habitat complexity might enhance trophic cascades and impact positively productivity by mediating trophic interactions among predators. Overall, interactions between species diversity at higher trophic levels and habitat structure can significantly alter ecosystem function in natural systems.