Browsing by Subject "Coccinellidae"

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    Arthropod Predation in Brassica Agroecosystems: Effects of Latitude, Community Composition, and Diet Breadth
    (2020-04) Gray, Hannah
    Arthropod predators provide crucial pest management services by consuming herbivore prey in agroecosystems. Yet, variation in arthropod predation strength among cropping systems and regions can prevent farmers from taking advantage of this alternative pest management strategy. This research examines underexplored potential causes of variation in arthropod predation in agroecosystems. Arthropod predation increases at lower latitudes. However, it is unknown whether this gradient extends to agroecosystems. Diet breadth of an arthropod predator can influence whether a predator can adequately control resident herbivore populations and can impact predation in a community context by determining whether predatory taxa will compete over shared prey, attack each other as intraguild prey, or partition herbivore taxa into distinct prey niches. To assess the effect of latitude, I first compared predation rates on live and artificial sentinel prey in Brassica agroecosystems between the tropical Federal District, Brazil and temperate Minnesota, United States. Contrary to expectations, I found that predation rates on all bait types were similar between the two localities and that reduced predation rates in the Federal District may be related to higher prey densities. Next, to further explore latitudinal effects, I assessed predation rates in Brassica agroecosystems across 15 degrees of latitude in the United States and 21 degrees of latitude in Brazil. Surprisingly, my results revealed a reverse predation gradient whereby arthropod predation increased with latitude in both countries. To examine the role of diet breadth, I first tested methods to improve molecular gut content analysis of arthropod predators by verifying broad metabarcoding results with species-specific melting curve analysis. This study documented common false positive and false negative taxonomic results and suggested that a species-specific verification step is necessary to ensure accurate depictions of arthropod trophic interactions. Lastly, I use the results of the gut content analysis to characterize the diet breadth of three coccinellid predator species (Coleomegilla maculata, Hippodamia convergens, and Harmonia axyridis) collected from a Brassica agroecosystem in Minnesota. I found that both herbivore and intraguild prey consumption were common among coccinellid species, but that C. maculata was least likely to engage in intraguild predation of fellow coccinellids.
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    Does a natural enemy limit the diet breadth of a generalist predator?
    (2015-05) Prescott, Kristina
    Abstract This dissertation explores the ways in which predators respond to novel prey, and in particular, how interactions among predators shape the habitat and prey use of predatory insects. Although predator habitat and prey use are commonly described in terms of responses to prey quality and density, interactions among predators may also be very important. In many systems, predators consume not only herbivorous prey, but also predators within their feeding guild. This interaction, termed intraguild predation, can alter the habitat use of predators that also act as prey, and thus limit access to some prey. Using a system in which a predator is simultaneously confronted with a novel prey and an aggressive intraguild predator, I consider how these forces work together to shape predator prey use. Aphid-feeding lady beetles have been extensively studied due to their importance in suppression of agricultural pests. Moving from habitat to habitat over the course of a growing season, they prey upon diverse aphid (and other) species. Although many species seem to aggregate in the areas with the densest aphid populations, others deviate from this expectation, particularly in responding to a novel resource. For example, the predatory lady beetle Coleogilla maculata, native to the Americas, seldom feeds on the soybean aphid, established in the Midwestern United States in 2001. To better understand the factors limiting the prey use of the native predator, I conducted a series of field experiments in maize and soybean, as well as laboratory predation trials, emphasizing the potential role of intraguild predation in limiting prey use by the native. This work establishes that use of soybean habitats by the native coccinellid is very limited, particularly with regard to laying eggs, and that contact between the native species and an aggressive intraguild predator, Harmonia axyridis, is extensive. However, studies of field patterns in survivorship and predation on sentinel eggs suggest that predation by the exotic does not exclude the native from soybean habitats. Lastly, I examine the potential for cannibalism to explain the coexistence between these two species.