Browsing by Subject "Novel Hosts"

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    Influence of temperature on development of eastern larch beetle Dendroctonus simplex LeConte and reproductive success in two novel Larix hosts
    (2024-07) Picklo, Rose
    Eastern larch beetle, Dendroctonus simplex LeConte (Coleoptera: Curculionidae: Scolytinae), is a bark beetle native to North America that feeds and reproduces in the phloem of its host, the eastern larch (tamarack) Larix laricina (Du Roi) K. Koch. As of 2024, approximately 75% of eastern larch forest type in Minnesota has been impacted by an ongoing eastern larch beetle outbreak that began in 2001. Climate is proposed as a major factor for the outbreak as longer and warmer growing seasons result in higher beetle populations. My thesis research evaluates how temperature affects each stage of eastern larch beetle development and tests the reproductive success of the beetle in two potential novel hosts, western larch (Larix occidentalis Nutt.) and subalpine larch (Larix lyalli Parl). In the first chapter, I used phloem sandwich assays to observe development of each life stage of eastern larch beetle at six temperatures ranging from 8°C-27.9°C. A developmental delay indicative of a facultative, pre-pupal diapause was identified within third and fourth instar larvae when exposed to temperatures below 14°C and 17°C, respectively. In the second chapter, I compared the reproductive success of eastern larch beetle in cut bolts of western larch and subalpine larch to its native host, eastern larch, in a host suitability study. I observed that the eastern larch beetle is capable of reproduction in all three hosts, and that the beetle performed similarly in eastern and subalpine larch. As global change facilitates introduction and range expansion of insect pests, these findings indicate that eastern larch beetle may pose a future threat to subalpine larch, should range expansion occur.
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    Potential host use by the Mediterranean Pine Engraver on Novel Tree Species.
    (2009-05) Walter, Abigail Jan
    Introduced species have the potential to cause great environmental damage, but many species introduced to an area will not have a large impact. It is critical that we develop the ability to predict which species will become damaging invaders, and manage ecosystems to minimize the probability that introduced species could establish. I present research results on the potential of the Mediterranean pine engraver, Orthotomicus erosus (Wollaston), to utilize North American tree species as hosts. I confirm that several North American conifers, species of pine and spruce, are suitable for the development of O. erosus. I then investigate the host acceptance behaviors of adults in contact with the outer bark. I show that differences among species occur during boring into the outer bark, and that beetles bore into both suitable and unsuitable tree species. The behavior of beetles before they are in contact with the bark was investigated with an olfactometer; odors from several conifer species do not affect the behavior of adult beetles. I also test the feeding response of beetles to extracts of bark and phloem chemicals. Several extracts contain feeding incitant or stimulant compounds, but the presence of these compounds in various tree species is different than adult bark boring behavior on those species. Finally, I used the data from my previous experiments and the phylogenetic distance among tree species in an attempt to predict the response of O. erosus to a second set of tree species from independent validation experiments. Phylogenetic distance from species with known beetle responses was not a good predictor of beetle response to novel plants. This body of work shows that O. erosus may accept a larger set of trees than are suitable for reproduction. Furthermore, adult host acceptance behavior is not determined solely by gustatory stimuli. Detailed knowledge about the stimuli governing host acceptance behavior is needed to predict the acceptability of new tree species to the beetle. The presence of acceptable but developmentaly unsuitable plants may determine whether species such as O. erosus are able to establish in a new environment.