The hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), is an invasive pest from Japan that is causing significant hemlock mortality in the eastern U.S. The most promising control method is biological control. Beetles in the genus Laricobius are adelgid specialists. In 2005, Laricobius osakensis, was discovered in Japan and in 2010 was approved for release in the eastern United States and there have now been more than 60 releases. In 2014, the polar vortex resulted in significant HWA mortality in the eastern U.S., depleting the food source for L. osakensis, which resulted in low field recoveries of them. In the 2015-2016 field season, there were 14 larvae recovered from the field, and the 2016-2017 field season yielded 90 larvae. A significant correlation was found between Laricobius beetles recovered and HWA density, between HWA density and plant hardiness zone, and a negative correlation between Laricobius beetles recovered and average tree health. Understanding more about the supercooling point of L. osakensis gave insight to its ability to survive subfreezing temperatures as occurred in 2014. Comparison of the supercooling point between the northern and southern populations of L. osakensis, and to the other released HWA predator, L. nigrinus, will allow us to determine which biological control agent is best suited for release in the coldest regions. The overall mean supercooling points of northern L. osakensis was -13.52 oC, southern L. osakensis was -13.42 oC, and L. nigrinus was -13.57 oC. There were no significant differences between species or populations. / Master of Science in Life Sciences / The hemlock woolly adelgid (HWA) is an invasive insect species from Asia that is the most important pest of eastern and Carolina hemlock trees in the eastern U. S. Laricobius osakensis is a small beetle from Japan that feeds only on HWA, and been released since 2012 in the eastern United States to control HWA populations. It is important to determine if L. osakensis populations were able to survive and spread in the eastern United States, and if the predator has an effect on HWA populations and the health of hemlock trees. In 2014, extreme cold temperatures in Virginia resulted in wide-scale death of HWA populations, depleting the food source for L. osakensis. Consequently, only 17 L. osakensis beetles were found on hemlock trees near release sites; however, the following year, 147 beetles were found. The ability to survive extreme cold temperatures is important for selecting a biological control agent for release in such regions. We can find out information about how tolerant a species is to cold temperatures by determining the supercooling point, the temperature at which it cannot stop itself from freezing. In this study we compared the supercooling points of a northern and southern population of L. osakensis, as well as another previously released and established biological control agent of HWA, Laricobius nigrinus. I found that there was no significant difference in supercooling point between the different types of Laricobius beetles suggesting that none of these species or populations appears to be anymore cold tolerant than the other for release in the colder regions of the U. S.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/82712 |
| Date | 29 March 2018 |
| Creators | Toland, Ashley Anne |
| Contributors | Entomology, Salom, Scott M., Mullins, Donald E., Kring, Timothy Joseph, Kuhar, Thomas P. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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