Application of Photorhabdus luminescens on control of the invasive fire ant Solenopsis invicta
Date Issued
2016
Date
2016
Author(s)
Lee, Chi-Lung
Abstract
Since first report in late 2003, the invasive fire ant, Solenopsis invicta, has spread at least half of northern Taiwan despite intensive control effort involving bait broadcasting and individual mound injection. Considering limited resources, developing alternative control methods that are more economical is urgently needed. The present study therefore aims to evaluate biocontrol potential of Photorhabdus luminescens, a symbiotic bacterium in entomopathogenic nematode Heterorhabditis brevicaudis. During proliferation P. luminescens yields toxic proteins that possess insecticidal activities, thus serving as biopesticide for pest control. The P. luminescens broth of different protein concentrations (0.5, 0.25, 0.125 and 0.05 mg/mL) were fed to colonies of S. invicta, accumulated mortalities are generally concentration-dependent, except for those treated with the broth containing 0.125 and 0.05 mg/ml protein which showed no difference with control. Control effect of broth is relevant to preserved days under room temperature. Broth preserved for 15 days could cause 39.93 % mortality; 100-day preservation broth displayed no controlling effort. Oral toxicity treatments of different protein molecular weights (greater than 100 kDa and 10–100 kDa) are not significantly with each other. To employ this liquid-based agent, direct broth application and broth embedding measures can be adopted. Behavioral tests showed that ground-dwelling S. invicta displayed no significant preference on control soil over those treated with P. luminescens broth, indicating negligible repellency of the broth. A bait delivery system was designed using microencapsulation where the broth is surrounded by a coating to retain its physical and chemical property. Capsules (4 mm in diameter) were prepared with a formula of core-shell ratio of 2:1, 1.4 % sodium alginate solution, 5 % calcium chloride solution and 10 % sucrose. Treatment of 100 microcapsules application caused significantly higher accumulated mortality (33.31 %), implying that broth dosage is responsible for fire ant mortality as well. When executing this strategy against fire ants, the amount of applied capsules must be evaluated; improvements of attractiveness and lethality are also required. Besides, other control methods can be combined as well to establish an integrated pest management framework.
Subjects
biocontrol
microencapsulation
Photorhabdus luminescens
Solenopsis invicta
Type
thesis
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