Annual bluegrass weevil (Listronotus maculicollis Kirby) (Coleoptera: Curculionidae) (ABW) is a major pest of annual bluegrass (Poa annua L.) and creeping bentgrass (Agrostis stolonifera L.) on golf courses in the northeastern United States. The asynchronous life cycle makes managing ABW difficult, putting emphasis on scouting to achieve accurate insecticide timing and acceptable control. Little is known about the biology and management of ABW in Virginia's more temperate climate. Reported cases of ABW resistance to pyrethroids (IRAC Group 3) continues to grow in the northeast, yet no pyrethroid-resistance cases have been reported in Virginia outside of the metropolitan Washington, D.C. For this thesis, I confirmed the widespread distribution of ABW across Virginia with a survey of golf course superintendents. Two golf courses in southwestern Virginia were monitored weekly during the 2019 and 2020 growing seasons to determine the seasonal biology of ABW within this region. These data suggest that overwintering ABW emerge much earlier than described in the northeast, with adult weevil activity beginning in late February or early March. I observed three complete ABW generations, with a potential fourth generation. Soil plugs from the same two golf courses were used to compare the salt floatation and Berlese-Tullgren funnel methods of larval extraction. The methods were highly correlated (R2 = 0.7856), suggesting either method is appropriate for ABW larval extraction. Bioassays conducted on adult ABW from the same two golf courses showed that field rate concentrations of the pyrethroid bifenthrin showed variable mortality ranging from 20% to 80% suggesting the presence of resistance genes in the population. A 100-fold rate of bifenthrin resulted in 100% mortality of ABW, however. Because cross-resistance has been reported among northeastern ABW populations, the common insecticide active ingredients chlorpyrifos (IRAC Group 1B: Organophosphate), trichlorfon (IRAC Group 1B: Organophosphate), λ-cyhalothrin (IRAC Group 3: Pyrethroid), α-cypermethrin (IRAC Group 3: Pyrethroid), imidacloprid (IRAC Group 4A: Neonicotinoid), and spinosad (IRAC Group 5: Spinosyn), were tested on ABW adults. In another bioassay, two organophosphates, trichlorfon and chlorpyrifos, resulted in significantly higher ABW mortality rates than all other labeled insecticides (P < 0.0001). Two other larvicides, spinosad and α-cypermethrin, also exhibited adult control, an important factor to consider for ABW management and preventing pyrethroid-resistance. These results provide valuable insight into the seasonal biology and management of ABW in Virginia and direction for further investigation into these populations. / Master of Science in Life Sciences / Annual bluegrass weevil (Listronotus maculicollis Kirby) (ABW) is a tiny, but damaging insect pest of cool-season golf course turfgrasses in the northeastern United States. As pest populations have spread southward, ABW has become an emerging pest in Virginia. The objectives of this thesis were to 1) determine the geographic distribution and seasonal biology of ABW in Virginia, 2) compare two methods for extracting ABW larvae from turf cores in order to estimate larval densities, and 3) to assess the susceptibility of ABW to various insecticides commonly used by golf course superintendents. A survey of golf course superintendents in 2019 revealed widespread prevalence of ABW across Virginia, particularly in areas growing predominantly cool-season turfgrasses. Two golf courses in southwestern Virginia were monitored weekly during the growing seasons of 2019 and 2020 to determine the seasonal biology of ABW. Data suggest that overwintering ABW emerge much earlier than reported in the northeast, with adult weevil activity beginning in late February or early March compared to April in the northeast. In addition, I detected three complete ABW generations, with a possible fourth generation occurring. Soil plugs from two golf courses were used to compare a heat extraction method using a Berlese-Tullgren funnel with the traditional salt float method for extraction of ABW larvae. The two methods extracted similar numbers of ABW larvae suggesting that either method is appropriate for ABW larval extraction. Adult ABW from the same two golf courses were collected and subjected to the pyrethroid insecticide bifenthrin at 0.128 kg ai ha-1 (field application rate), 1.28 kg ai ha-1 (10-fold rate), 12.8 kg ai ha-1 (100-fold rate), along with a water control. Results indicated that the field application rate of bifenthrin killed > 50% but <90% of ABW adults, suggesting that some resistance may be present in the population. A concentration of 100-fold bifenthrin field rate killed 100% of tested individuals, suggesting that widescale field resistance to pyrethroids is likely not present. Because cross-resistance has been reported among northeastern ABW populations, the common insecticide active ingredients chlorpyrifos (IRAC Group 1B: Organophosphate), trichlorfon (IRAC Group 1B: Organophosphate), λ-cyhalothrin (IRAC Group 3: Pyrethroid), α-cypermethrin (IRAC Group 3: Pyrethroid), imidacloprid (IRAC Group 4A: Neonicotinoid), and spinosad (IRAC Group 5: Spinosyn), were tested on ABW adults from the same two golf courses. Two organophosphates, trichlorfon, a larvicide, and chlorpyrifos resulted in significantly higher ABW mortality rates than all other active ingredients (P < 0.0001). Two other larvicides, spinosad and α-cypermethrin, also exhibited adult control, an important factor to consider when attempting to manage ABW and preventing resistance to pyrethroids. Our results provide valuable insight into the seasonal biology and management of ABW in Virginia and direction for further investigation into these populations.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/104174 |
| Date | 14 July 2021 |
| Creators | Daly, Emeline Hope |
| Contributors | Plant Pathology, Physiology and Weed Science, McCall, David S., Kuhar, Thomas P., Goatley, James Michael |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Coverage | Virginia |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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