Browsing by Subject "parasitoid"

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    Data and code for forecasting overwintering mortality of Spathius galinae in North America
    (2021-04-26) Wittman, Jacob T; Aukema, Brian H; Duan, Jian J; Venette, Robert C; wittm094@@umn.edu; Wittman, Jacob T
    From publication: Evaluating the cold tolerance of biological control agents is often necessary to optimize their release and performance. We used field and laboratory assays to determine the cold hardiness of the parasitoid Spathius galinae Belokobylskij & Strazanac, an approved classical biological control agent of emerald ash borer (Agrilus planipennis Fairmaire) in North America. Supercooling points and lower lethal temperature of mature (cocooned) S. galinae larvae were measured in controlled cooling assays in the laboratory. Most S. galinae larvae died after reaching their supercooling point, which occurred at -25.0°C on average. Several larvae, however, initiated freezing but later eclosed, suggesting S. galinae may be partially freeze tolerant. Supercooling points were not affected by chilling rate. In the winter of 2019 – 2020, we monitored development of mature S. galinae larvae in ash segments above and beneath the snow in three locations in Minnesota, USA. Nearly 100% of S. galinae larvae died after air temperatures reached -29°C in Minnesota. Using models developed from our data, we forecast eclosion rates of S. galinae based on minimum winter temperatures across the range of ash (Fraxinus spp.) in North America. Our results indicate that S. galinae populations may suffer high overwintering mortality in areas where winter temperatures regularly decrease below -28°C, but a small portion of the population may be able to survive lower temperatures.
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    Population Ecology Of Aphelinus Certus, An Adventive Parasitoid Of Soybean Aphid In North America, With Implications For Biological Control
    (2020-05) Miksanek, James
    Parasitoids are excellent model systems in addressing fundamental aspects of biology and ecology while offering a high degree of economic and ecological value in regulating the population densities of their host species in both natural and agroecological settings. The single most important arthropod pest of soybean is the soybean aphid (Aphis glycines). Although not recommended for release due to its broad host range, the parasitoid Aphelinus certus has since been accidentally introduced into North America and has been hypothesized to be a key natural enemy of soybean aphid. However, the overall impact of A. certus in the biological control of soybean aphid is uncertain. The chapters in this thesis are united by broader theories and concepts addressing the role of A. certus in biological control. Chapter 1 presents a coupled-equations matrix population model parameterized by a series of laboratory bioassays outlining the life history of soybean aphid and A. certus; analysis of the model suggested that a parasitism rate of 0.21 d−1, which would be equivalent to at least 3.4% mummies, is capable of maintaining soybean aphid below economically damaging levels in 31.0% of simulations. Chapter 2 further explores the effects of host density on parasitoid lifespan and reproduction as well as establishes a quantitative wing wear index for estimating the age of field-collected parasitoids. Moving from theoretical to in-field efficacy, Chapter 3 evaluates the impact of A. certus on soybean aphid in soybean fields across central and western Minnesota (United States) from 2017–2019; contrary to the predictions of the model in Chapter 1, the results of this field experiment did not find a strong effect of A. certus in reducing the population growth rates of soybean aphid. Finally, Chapter 4 evaluates the prevalence of parasitism by A. certus on the native aphid species Aphis asclepiadis and Aphis monardae in prairie ecosystems; these results suggest that A. certus readily colonizes or is already established in natural habitats and poses a potential threat to endemic aphid populations. Lastly, I offer conclusions by more broadly discussing this work within the context of population dynamics, ecology, and biological control.
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    Transgenerational Fecundity Compensation And Post-Parasitism Reproduction By Aphids In Response To Their Parasitoids
    (2017-03) Kaiser, Matthew
    Increased reproductive effort by organisms in response to attack by consumers (‘fecundity compensation’) is well documented in both plants and animals, though most examples only involve direct compensation by the individuals exposed to consumers. In Chapter 1, I used the parasitoid wasp Lysiphlebus orientalis Starý & Rakhshani (Hymenoptera: Braconidae) and the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), to determine whether reproduction by parasitized aphids can lead to fecundity compensation. Although parasitism by L. orientalis strongly decreased fecundity for parasitized aphids, offspring of parasitized aphids reproduced at a greater rate at maturity than did the offspring of non-parasitized aphids. Also, parasitized aphids contained fewer but larger embryos developing within them. The presence of these larger embryos may explain how the offspring of parasitized aphids can produce more progeny with no apparent reduction in progeny quality. Mature and nearly mature A. glycines successfully reproduced after parasitism, a prerequisite for transgenerational fecundity compensation, and L. orientalis showed a preference for these age classes of aphids as hosts when foraging. This work is the first known demonstration of transgenerational fecundity compensation in an animal. In Chapter 2, I demonstrated that L. orientalis is able to suppress caged populations of A. glycines in spite of transgenerational fecundity compensation by parasitized aphids. Aphid populations exposed to parasitoids were driven to extinction within, on average, 8 or 11 weeks depending on the starting density of parasitoids. I also showed that transgenerational fecundity compensation has a relatively minor impact on modeled A. glycines populations. Instead, direct reproduction by parasitized aphids, as well as parasitoid host-stage preference, had stronger impacts. Finally, in Chapter 3, I showed that transgenerational fecundity compensation is not limited to the A. glycines – L. orientalis association, as it also occurs when Aphis craccivora Koch (Hemiptera: Aphididae) is attacked by both L. orientalis and Lysiphlebus fabarum (Marshall) (Hympenoptera: Braconidae). I also found that L. orientalis may prefer slightly older A. craccivora hosts than L. fabarum. These results indicate that while transgenerational fecundity compensation may be an interesting and novel physiological phenomenon present in multiple aphid-parasitoid associations, it may be relatively inconsequential for populations of aphids and their parasitoids.