Browsing by Subject "Aphis glycines"

Now showing 1 - 3 of 3
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    Integrating chemical and biological controls for management of soybean aphid
    (2016-11) Tran, Anh
    The soybean aphid, Aphis glycines Matsumura, is predominately managed by foliar application of broad-spectrum insecticides. Though broad-spectrum insecticides can provide immediate therapeutic control of A. glycines, the insecticides can negatively impact natural enemies. Natural enemies of A. glycines are important for suppressing aphid population. However, natural enemies are not integrated with A. glycines management. Within this thesis, I examine the ability of a new selective insecticide to suppress A. glycines population and conserve natural enemies. I also develop a sampling plan that can estimate natural enemy populations with a desired level of precision. The results from these studies will provide information on how to better integrate natural enemies into current A. glycines management programs.
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    Risk and efficacy in biological control: an evaluation of the aphid parasitoid Aphelinus certus in North America
    (2016-09) Kaser, Joseph
    Invasive species are causing increasing harm to native biodiversity, ecosystems, agriculture, and other natural resources. Classical biological control is a powerful and cost-effective strategy for long-term invasive species management. However, while importation of biological control agents has many potential benefits, it also entails risks, such as harm to non-target native species. Therefore, candidate biological control agents are studied prior to release to predict their safety. Little is known, however, about how traits affecting the safety of biological control agents may also impact their efficacy in terms of reducing invasive pest populations. In this dissertation, I investigate the interacting causes and consequences of risk and efficacy in biological control. I approach this investigation first from a theoretical standpoint, including a literature review and a mathematical modeling framework. I then investigate the aphid parasitoid Aphelinus certus Yasnosh (Hymenoptera: Aphelinidae) which attacks the invasive soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae). In the early 2000s, Aphe. certus was evaluated as a potential classical biological control agent of the soybean aphid, but it was precluded from release due to concerns over ecological safety. However, the parasitoid was accidentally introduced anyway, and thus provides an interesting case study to evaluate the causes of and consequences of biological control risk and efficacy. Chapter 1 of this dissertation provides a literature review and synthesis of the potential impacts of natural enemy-mediated indirect effects on both risk and efficacy in biological control. Polyphagous natural enemies cause various indirect interactions between their prey/host populations. These indirect interactions may be reciprocally negative (i.e. apparent competition), but can be any combination of positive, negative, or neutral. I focus on parasitoids to illustrate the importance of natural enemy-mediated indirect interactions in biological control risk-benefit assessment. In Chapter 2, I utilize a mathematical modeling framework to investigate direct and indirect interactions between a generalized biological control agent, and its target and non-target hosts. I use Nicholoson-Bailey form difference equations to simulate a one-parasitoid two-host system, and I evaluate conditions under which biological control safety and efficacy interact. Apparent competition can have important benefits for increasing biological control efficacy, even at low levels of non-target impact. However, under conditions of parasitoid egg limitation, high attack rates on resistant non-target hosts can dramatically decrease biological control efficacy while concurrently increasing non-target risk. These findings are discussed in the context of biological control agent pre-release risk-benefit assessment. The code for an interactive application of this model is provided as supplementary material for Chapter 2, and is presented in the Appendix. In Chapter 3, I investigate the potential for perennial biofuel plantings to enhance biological control of the soybean aphid by parasitoids. Cultivated biofuels provide an important source of renewable energy, and may provide additional ecosystem services, such as enhanced natural enemy communities and increased biological control of pests in neighboring crops. I conducted a large-scale randomized experiment to test for effects of biofuel plantings on biological control of the soybean aphid in surrounding soybean fields. There was no significant effect of any biofuel treatment on the parasitoid community or on soybean aphid density compared to controls. However, the experiment coincidentally captured the early colonization stages of the introduced aphid parasitoid A. certus in Minnesota. Aphelinus certus is increasing in density in Minnesota soybean fields, and this increase corresponds with a decrease of resident Aphidiinae parasitoids over a three-year period. In Chapter 4, I present an evaluation of the host range of A. certus. I exposed A. certus to 17 species of aphid hosts in no-choice tests. Aphelinus certus attacked most species presented to it, but mummification rates and adult emergence were highly variable. I mapped host use data onto an aphid phylogeny to see if host phylogeny predicted host use. Aphelinus certus mummification significantly clustered with host relatedness (P=0.043). Several native aphid species are shown to be at risk of attack by A. certus. Additionally, several pest aphid species present in North America may also be subjected to biological control by A. certus. In Chapter 5, I evaluate the biological control impact of A. certus on the soybean aphid. The observed increase of A. certus prevalence in North American cultivated soybeans does not necessarily indicate that the parasitoid is substantially contributing to soybean aphid biological control. I conducted an exclusion-cage experiment designed to isolate the impact of parasitoids compared to other resident natural enemies of the soybean aphid. I found that A. certus greatly outnumbered all other soybean aphid parasitoids, and that it significantly reduced soybean aphid populations over a time span of less than two weeks compared to controls (P<0.0001). Moreover, parasitoids alone resulted in aphid densities that were statistically equivalent to the combined effect of predators and parasitoids (P=0.95). These results indicate that A. certus is an important new component of the soybean aphid natural enemy community in North America. Aphelinus certus provides an informative example of a biological control agent that is effective but also risky in terms of non-target impact to native species.
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    The role of entomopathogenic fungi in the management of Soybean Aphid.
    (2011-07) Koch, Karrie Anne
    Soybean aphid, Aphis glycines Matsumura, is an invasive arthropod pest of soybean which has been present in North America since 2000. Aphid outbreaks cause economic damage via increased insecticide use and reduced yield. Management of this pest has been achieved almost exclusively with foliar applications of broad spectrum insecticides. The purpose of this research is to determine how a fungal pathogen of soybean aphid, Pandora neoaphidis, can contribute to the natural regulation of aphid populations. Pandora neoaphidis is an endemic aphid pathogen and the most frequently reported pathogen infecting soybean aphid. Analysis and field validation of a mathematical model describing the soybean aphid-P. neoaphidis pathosystem has shown that the fungus can establish and persist when aphid densities are lower than the economic threshold of 250 per plant; thus confirming that P. neoaphidis is capable of contributing to aphid control before aphids reach damaging densities. Additionally, field experiments demonstrate that emerging aphid management tactics including aphid-resistant soybean plants and insecticide seed treatments have minimal impacts on aphid infection rates by P. neoaphidis and are likely compatible with this natural enemy. Cage studies demonstrate that the presence of Harmonia axyridis in soybean aphid colonies also harboring P. neoaphidis has no impact on aphid infection by the fungus. Pandora neoaphidis may also be an important regulator of aphid populations on the aphids’ primary host, Rhamnus cathartica, or common buckthorn, as soybean aphid morphs which occur on this host are the most susceptible to infection. However, fungicide applications to soybean can have lasting impacts on the beneficial fungi infecting soybean aphid as foliar fungicide applications to soybean reduced the rate of aphid infection both before and after aphids moved to the primary host in the autumn. In summary, P. neoaphidis is likely an important member of the natural enemy community which provides a significant level of aphid biological control.