Dissertation

Autodissemination of Beauveria bassiana as a Strategy to Manage Melon Flies (Zeugodacus cucurbitae) and Oriental Fruit Flies (Bactrocera dorsalis) in Hawai’i

Pennington, Sarah Kirstin

2025

Overview

Fruit flies (Diptera: Tephritidae) are major agricultural pests globally, capable of causing devastating crop losses. These pests have restricted Hawai‘i’s fruit export opportunities, caused millions in annual crop losses, and discouraged fruit production due to high control costs. The ongoing pressure from fruit flies in Hawai‘i highlights the limitations of current control strategies and the urgent need for new approaches. Entomopathogenic fungi have lower environmental impacts than chemical insecticides, and decades of research show that they can cause high mortality in tephritids. Entomopathogenic fungi autodissemination devices are a promising developing innovation for tephritid management. By using male-attracting, species-specific parapheromone lures in the autodissemination device, male flies can act as vectors to transfer fungal spores to sexually-mature females. Our lab developed a novel oil-based formulation of entomopathogenic fungi Beauveria bassiana and a 3D-printed autodissemination device. In this study, I tested the ability of our autodissemination device to suppress populations of the two most abundant invasive tephritid species in the state- melon flies (Zeugodacus cucurbitae) and oriental fruit flies (Bactrocera dorsalis).Current tephritid control strategies rely heavily on insecticide-laced bait sprays, mainly containing Spinosad, leading to elevated resistance levels in several wild melon fly and oriental fruit fly populations in Hawai‘i. First, I used lethal concentration assays to assess population-level variation in B. bassiana and Spinosad susceptibility in wild and laboratory melon fly and oriental fruit fly colonies. I found B. bassiana could induce high mortality in both highly Spinosad resistant and susceptible melon fly colonies. Next, I conducted laboratory trials to 1) evaluate the autodissemination device’s ability to facilitate horizontal transfer of spores from male to female flies, and 2) determine if the autodissemination device can cause significant mortality in melon fly and oriental fruit fly populations. Results showed clear evidence of horizontal spore transfer and that the autodissemination device could induce significant mortality in both species.Finally, I conducted four field trials to assess the ability of our device to reduce melon fly and oriental fruit fly populations on commercial farms in Hawai‘i. In three field trials, we demonstrated that the autodissemination device could reduce melon fly populations. However, in the one field trial targeting oriental fruit flies, fly populations were not reduced- possibly because of the shorter treatment period and differing farm management practices. Together, these results demonstrate that our autodissemination device can reduce tephritid fruit fly populations, and could be a valuable addition to current management strategies.

• Publisher: ProQuest Dissertations & Theses
• Subject: Agricultural chemistry / Agriculture / Entomology / Microbiology
• ISBN: 9798293879571