Browsing by Subject "parasitoids"
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Item Behavioral ecology of parasitoid diet breadth and insect defenses(2017-07) Stenoien, CarlOne of the primary challenges animals face is consuming enough nutrients of sufficient quality that they might realize their reproductive potential. Many strategies have evolved, but robust explanations for the causes and consequences of variation in diet breadth remain elusive. I’ve used field and comparative lab studies of a specialist parasitoid wasp (Pteromalus cassotis) with a closely-related generalist (Pteromalus puparum) across several potential butterfly host species to better understand how physiological and behavioral trade-offs might limit parasitoids' host ranges. When paired with eleven host species, both parasitoids preferred those hosts on which they performed best, but I found little support for the idea that physiological trade-offs drive the evolution of specialized foraging strategies. Intriguingly, the generalist was more likely than the specialist to accept unsuitable hosts, while the specialist was more likely than the generalist to reject suitable hosts. I also reared monarch butterflies (Danaus plexippus) to be more or less chemically defended and found that host toxicity influenced the behavior and performance of the specialist. The generalist often killed monarch hosts, but was incapable of developing in them. Finally, I investigated the role of behavior in avoiding natural enemy-induced mortality of insect pupae, which are relatively immobile and are often presumed to be vulnerable to natural enemies. I review many examples to show that pupae likely benefit from a variety of behaviors performed before pupation (by the larva or pre-pupa), behaviors of the pupa itself, and behaviors of conspecific and heterospecific individuals. Taken together, my dissertation provides the first details on the natural history and chemical ecology of interactions between P. cassotis and the monarch butterfly. My findings suggest that, in some cases, behavioral decisions may be more important than physiological trade-offs in shaping animal diet breadth. These findings have implications for organisms in rapidly changing environments and biological control efforts because they demonstrate that specialist foragers may retain the evolutionary potential for host switches, and generalists can cause difficult-to-measure non-target mortality.Item Evaluating biological control of the soybean gall midge (Resseliella maxima Gagné) in Minnesota(2023-12) Melotto, GloriaThe soybean gall midge, Resseliella maxima Gagné (Diptera: Cecidomyiidae), poses a threat to soybean crops in the Midwest US. However, little is known regarding its natural enemies and the potential for biological control. Therefore, this thesis aims to fill this knowledge gap by focusing on evaluating biological control for R. maxima. To achieve this, we conducted a two-year survey to investigate the parasitoid and predator communities associated with R. maxima infestations in Minnesota. Our findings confirmed parasitism of R. maxima larvae by the wasp Synopeas maximum Awad & Talamas (Hymenoptera: Platygastridae) and examined the spatial-temporal dynamics of parasitism within fields. Additionally, our observations showed that the predator Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) was the most prevalent species in the soybean fields in this study, presented temporal overlap with the pest, and had a high propensity to feed on R. maxima larvae. We concluded that further research should evaluate how parasitism rates by S. maximum could be promoted in production fields and that Pt. melanarius should receive further attention as a potential biological control agent of R. maxima.Item Risk and efficacy in biological control: an evaluation of the aphid parasitoid Aphelinus certus in North America(2016-09) Kaser, JosephInvasive 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.