M.S. - Entomology

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    Gut microbial communities of Plutella xylostella vary among Hawaiian island populations
    (2024) Montoya-Pimolwatana, Maya Louise; Jani, Dr. Andrea; Shikano, Dr. Ikkei; Entomology
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    Developing a Fungal Based Trapping Station for the Control of Fruit Flies (Diptera: Tephritidae) in Hawaii
    (University of Hawaii at Manoa, 2023) Streit, Christian; Shikano, Ikkei; Entomology
    Fruit flies (Diptera: Tephritidae) are a cosmopolitan species with many members of this family known to be economically significant pests. Research to understand the lifecycles and unique behaviors of these flies have been important to exploit critical points of development to control their populations. Many management strategies have been proposed, studied, and implemented across the world and have been met with success. But, with the ability of these flies to disperse, not all methods are applicable or successful in all regions. Entomopathogenic fungi are being studied in conjunction with the Tephritidae to determine efficacy against all life stages. Entomopathogenic fungi are capable of inducing high rates of mortality in adult fruit flies. The limiting factor of entomopathogenic fungi is its susceptibility to UV radiation. For this reason, it is widely used as a soil drench. Development of a product that incorporates entomopathogenic fungi to target adult fruit flies would be far more efficacious, adding one more tool to a widening array of management tools. Multiple stages of testing and development were performed, starting with determining the efficacy of Beauveria bassiana against three invasive tephritid fruit flies in Hawaii: Bactrocera dorsalis, Ceratitis capitata, and Zeugodacus cucurbitae. After confirming that B. bassiana kills adult fruit flies, we determined the lethal concentrations and developed a formulation that would be effective in a passive bait station, which included incorporation of lures and thickening agents.The effectiveness of each addition or modification to the formulation was assessed by measuring the mortality of exposed flies and the numbers of spores they picked up. The developmental goal of creating a formulation that could be vectored and dispersed across a population via horizontal transmission was confirmed, at least in lab cage trials. This fungal formulation could potentially be used as a new IPM tool for the control of tephritid fruit flies in both conventional and organic cropping systems.
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    Dietary Effects Of Prosopis Pallida On Apis Mellifera Health In Hawai‘i
    (University of Hawaii at Manoa, 2023) Hausler, Daniel; Wright, Mark G.; Entomology
    Pollen is a honey bee’s primary protein and lipid source and the availability, quality, quantity, and diversity of a bee’s pollen diet determine its individual health and, therefore, the overall health of the entire colony. Common kiawe (Prosopis pallida, Fabaceae) grows in the arid valleys of the leeward regions of all the Hawaiian islands and is a widely available food source for honey bees. This study aimed to determine the impact of kiawe pollen nutrition on colony health. To address this, I identified bee-collected pollen and analyzed its nutritive quality individually from apiaries on O‘ahu and Maui over a period of 14 months. Pollen was collected monthly, sorted by color as a proxy for species, and total proteins and lipid content quantified. Colony health metrics, including brood quality, frame occupancy of hive bees, and varroa and small hive beetle numbers, were also assessed monthly. Results showed there is spatial and monthly variation in kiawe pollen’s total protein and lipids, as well as a variation in hive health metrics and bee-collected pollen diversity. On Maui, SHB levels never significantly differed from each other, and were highest in June (10.12 ± 1.78). SHB levels on O‘ahu were highest in April (48.3 ± 7.61) while percent varroa mite infestation on O‘ahu was highest in January (5.67 ± 1.32). Mean brood quality was significantly higher on Maui (81.41 ± 0.43) compared to O‘ahu (78.33 ± 0.49). Also, mean frames of bees were significantly higher on Maui (14.73 ± 0.20) compared to O‘ahu (5.35 ± 0.11). Lipids levels were highest on Maui in June (14.28 ± 0.22 mg/g pollen) and highest on O‘ahu in September (15.48 ± 2.07 mg/g pollen), while protein levels on Maui were highest in January (326.28 ± 11.55 mg/g pollen) and highest on O‘ahu in February (361.53 ± 23.09 mg/g pollen). Additionally, the proportion of kiawe pollen in the homogenate (average percent total from six, 25 mL subsamples) increased during the kiawe blooming seasons (percentage was highest in March with 46.47 ± 6.34%) but these months did not display any change in hive health. Kiawe macronutrient quality did not significantly impact hive health metrics and hive health seemed more influenced by the absence or presence of varroa mites, showing that hives on O‘ahu are much more stressed than hives on Maui.
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    Fumigant Toxicity of Essential Oils Against Frankliniella occidentalis, F. insularis (Thysanoptera: Thripidae), and Solanum lycopersicum (Solanceae) as Affected by Polymer Release and Adjuvants
    (University of Hawaii at Manoa, 2022) Gharbi, Karim; Tay, Jia-Wei; Entomology
    Some species of thrips have become significant agricultural pests due to their cosmopolitan distribution, feeding damage and vectorial capacity for plant viruses. However, control of this pest is complicated by their life cycle and resistance to conventional insecticides. I sought to explore a novel method of thrips control that addressed these resistance mechanisms by applying essential oils as fumigants. These essential oils included (R)-linalool, racemic linalool, or a binary combination of (R)-linalool with one of twelve other oils (i.e., peppermint, cedarwood, neem, clove, coconut, jojoba, soybean, olive, α-terpineol, 1,8-cineole, trans-anethole and (R)-pulegone) with distilled water as a control. Essential oils were conditioned into hydrogels and exposed to a pesticide resistant species of thrips (Frankliniella occidentalis), a pesticide naive species (Frankliniella insularis), and a host plant of the former (Solanum lycopersicum). Thrips and tomatoes were first exposed separately in in vitro trials, and then together in caged-plant trials. Pure (R)-linalool and its binary mixture with peppermint oil were the most toxic to both species of thrips and tomatoes in in vitro trials. However, caged-plant trials revealed a greater level of resistance to essential oil fumigation than that predicted by in vitro trials. This resistance was attributed to behavioral resistance mechanisms precluded by in vitro trials. While certain essential oils have demonstrated potential as alternatives to conventional insecticides, glasshouse and field trials are necessary to fully quantify the extent to which the life history traits of thrips contribute to bioinsecticide resistance.
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    Trap Cropping For Bottom-up And Top-down Control Of Diamondback Moths (Plutella Xylostella) In Hawai‘i
    (University of Hawaii at Manoa, 2021) Pugh, Morgan Elizabeth; Shikano, Ikkei; Entomology
    Plutella xylostella, the diamondback moth (DBM), is a detrimental pests of many plants in the family Brassicaceae. Populations of DBM have become resistant to many types of pesticides. My thesis investigated the use of trap crops for the bottom-up and top-down control of DBM. The first research chapter examined the effects of putative dead-end trap crops on Hawaiian DBM. The second research chapter examined the role of the naturalized weed, Virginia pepperweed (Lepidium virginicum) on the behaviors of DBM and their natural enemies.To determine a suitable dead-end trap crop for use against DBM on cabbage (Brassica oleracea cv. K-K Cross) in Hawai`i, a series of larval feeding, oviposition, and survival experiments were conducted. The plants tested were Barbarea verna and two varieties of Lepidium sativum. All three plants have shown dead-end properties against DBM in North America and Europe. However, I found that Hawaiian DBM populations from O`ahu and Kaua`i behaved differently from these previous studies. The DBM populations used in this study only prefered to oviposit on one variety of L. sativum relative to cabbage, and showed no preference for the other two plants. More importantly, both DBM populations survived from egg to adult on all of the “dead-end” trap crops, just as well as they did on cabbage. Next, I examined the effects of L. virginicum on DBM feeding and oviposition behavior as well as the plant’s effects on the behavior of DBM natural enemies. A series of lab and field experiments were conducted to observe predation and parasitization activity on the L. virginicum compared to cabbage. DBM favored L virginicum relative to cabbage for both feeding and ovipostion. The endoparasitoid, Cotesia plutellae, favored L. virginicum for initial prey searching behavior and more DBM were parasitized on L. virginicum than on cabbage. In conclusion, the putative dead-end trap crops were unsuccessful in preventing the two populations in Hawai`i from completing their lifecycle. However, the naturally occuring weed, L. virginicum, may act as a different type of dead-end trap crop by harboring high numbers of natural enemies of DBM, which could help to control the pest.
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    Effects of Fiji disease resistant sugarcane varieties on the biology of Perkinsiella saccharicida Kirkaldy
    (University of Hawaii at Manoa, 1977) Taniguchi, Glenn Yukio.; Entomology
    Fiji disease is a virus disease of sugarcane, Saccharum officinarium L., and some closely related species. At the present time, Fiji disease is confined to Madagascar and the South-West Pacific area. This includes such sugarcane-growing areas as Australia
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    Deformed Wing Virus (DWV) Transmission Across Pollinators Of Hawai‘i
    (University of Hawaii at Manoa, 2020) Santamaria, Jessika; Villalobos, Ethel M.; Entomology
    These studies explore the impact Deformed wing virus (DWV) on the pollinators of Hawai‘i. DWV is a well-studied virus, now commonly associated with the European honey bee, Apis mellifera (Hymenoptera: Apidae), populations. The documented decline of honey bee populations worldwide led past researchers to determine this virus played a vital role in their dwindling numbers. Research attention had now shifted to look at the DWV presence in non-Apis communities in the mainland, but only recently has research explored the unique ecology Hawai‘i offers. The first chapter investigates the indirect role of the Varroa destructor mite, a honey bee pest, and how its introduction to the state of Hawai‘i in 2007, influences the continued spread of DWV, not only within honey bee communities, but to surrounding insect populations. In this study, we utilized the limited distribution of the Varroa mite in the Hawaiian archipelago to compare DWV prevalence on non-Apis flower visitors, and test whether Varroa presence is linked to a viral spillover to these populations. We select the two islands: O‘ahu, where V. destructor has been present since 2007, and Maui, where the mite remains absent. Individuals of A. mellifera, Ceratina smaragdula, and Polistes spp. were assessed and used to compare the DWV prevalence in the Hymenoptera community of the two islands. DWV was detected in the non-Apis Hymenoptera collected from O‘ahu but was absent from samples collected on Maui. These results suggest an indirect, but significant, increase on the DWV prevalence in the Hymenoptera community in mite-infected islands. The second study focused on the DWV prevalence in the bee genus, Hylaeus (Hymenoptera: Colletidae). The Hawaiian Islands are home to more than 60 endemic species of Hylaeus, commonly referred to as yellow-faced bees. Their ecological history and distribution are unique to the archipelago and their numbers have unfortunately dwindled in the past years. The decrease in populations have to do with many factors which include destruction of natural habitats, the introduction of predatory wasps, and the introduction of ants to the islands. The introduction of pathogens and diseases has also been suspected but not documented. We sampled populations of two non-native species of Hylaeus, on Oahu, to determine their DWV status. Additionally, DWV strains for these species are reported. For the first time, DWV presence was found for this genus in Hawai‘i. DWV viral levels of combined Hylaeus species were comparable to those of Hymenoptera in previous Hawai‘i studies. However, when divided across the two species, H. albonitens had almost twice the DWV prevalence when compared to H. strenuus. These results may indicate that despite being ecologically and evolutionarily closely related, DWV prevalence can still have great variability within a genus, and DWV strain types vary across non-Apis groups. The third chapter sets a foundation for future DWV research in Hawai‘i, by making a preliminary list of the groups of flower-visiting insects that carry DWV at sites where they overlap with honey bee populations. Pollinators, which rely on flowers as their food source, also encounter a myriad of pathogens when visiting these sites. Yet, determining when and which pathogen a pollinator will encounter during a flower visit is a difficult task. The disease interactions between flower visiting insects is a diverse and complex web, made up of many variables and factors. By mapping these interactions, we can start to better understand the spread of diseases between pollinator communities at these sites, especially when we consider the potential impact DWV may have on these communities. This survey, conducted over a period of 4 years, across various sites on the island of O‘ahu, explores the prevalence of DWV in different flower-visiting insects, and how these viral rates differ over time and across species.