Doctor of Philosophy (PhD)



Document Type



Twospotted spider mites, Tetranychus urticae, is an important agricultural pest of many field crops worldwide. This study investigated the impacts of imidacloprid seed treatments on populations of twospotted spider mites while also investigating if exogenous applications of jasmonic acid can offset any hormone modulating effects caused by seed treatments. Imidacloprid seed treatments significantly increased cumulative adult mite days in 2013 but not 2015 or 2016 in the field. Applications of 10 millimolar jasmonic acid did not reduce mite severity or injury in all field trials. Imidacloprid seed treatments significantly increased all spider mite life stages in the laboratory while applications of jasmonic acid significantly reduced all mite life stages on neonicotinoid treated and non-treated cotton. Seed treatments do not affect the host preference of twospotted spider mites compared to non-treated however, jasmonic acid applications reduced the host suitability of seedling cotton to only adult mites. Additionally, leaf dip bioassays were conducted to evaluate resistance levels to abamectin in 12 populations of T. urticae collected from the Midsouth. Louisiana populations were highly resistant with corresponding LC50 values of 0.082 and 0.184 ppm and resistance ratios of 630 and 1415-fold. One population from Mississippi was slightly resistant with an LC50 value of 0.0021 ppm and a resistance ratio of 11.1 compared with a susceptible control population. Finally, greenhouse and field applied foliar spray tests and leaf dip bioassays were conducted to examine the susceptibility of T. urticae to glufosinate ammonium in cotton. Leaf dip bioassay results indicated that T. urticae were highly susceptible to concentrations of formulated glufosinate ammonium. The LC50 value was determined to be 10.31 ppm. Field applied glufosinate ammonium at 1.61 and 3.14 L ha−1 provided 48.86 and 80.22 percent control while fenpyroximate provided 89.62 percent control 5 days after application in 2015. Greenhouse applications resulted in 55.43 percent control 14 days after application with 0.73 L ha−1 while 1.61 L ha−1 resulted in 72.86 percent control and 3.14 L ha−1 resulted in 91.85 percent control of T. urticae populations. Data generated from these studies provide useful information on integrated pest management of twospotted spider mites in Midsouth cotton.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Stout, Michael

Included in

Entomology Commons