Ph.D. - Entomology
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ItemEcological management of insect pests using cover crops in field crops and vegetables([Honolulu] : [University of Hawaii at Manoa], [August 2013], 2013-08)This dissertation researched diversified cropping systems created through habitat management techniques, exploring whether these habitats would alter pests' behavior and/or enhance beneficial insects, and contribute to suppress pest and disease complexes in corn production systems. An exploratory study through small-scale field experiments determined sunn hemp (Crotalaria juncea) as the potentially the most suitable species for further study. In the preliminary studies, sunn hemp intercropping reduced incidence of hopperburn and Maize mosaic virus (MMV) symptomatic plants caused by Peregrinus maidis feeding, and increased parasitism of Helicoverpa zea eggs by Trichogramma spp. on the corn silks. The reduced incidence of hopperburn and MMV was attributed to an increase in P. maidis within-field activity, resulting in reduced initial colonization on corn plants. The results showed a suitable intercrop might be useful for management of persistent viruses, which are usually considered unmanageable by habitat management to cropping systems. On the basis of these preliminary studies, experiments were conducted in large-scale field with a higher corn-to sunn hemp intercropping ratio to validate results and possibly contribute new pest management options for large-scale corn production systems. Increase in within-field P. maidis activity with resulting in lower incidence of MMV symptomatic plants in the sunn hemp-intercropped treatments were consistently similar to results that were obtained from small-scale field experiments. This strategy may contribute an important component of integrated pest management for reducing spread of persistently transmitted viruses in large-scale corn production systems. Greater parasitism of H. zea eggs by Trichogramma spp. in sunn hemp-intercropped treatments was consistently similar to that obtained from small-scale field experiments. These results suggested growing strips or patches of suitable cover crop may help in sustaining the populations of beneficial insects at the time of pest outbreaks. Augmentative biological control (releases of Trichogramma pretiosum in corn monoculture) resulted in a greater parasitism of H. zea eggs, and increased ear yield compared to habitat management (sunn hemp-intercropped). This result suggested H. zea management is important component to achieve economic yield and augmentative biological control is a more effective tool than the habitat management in cornfields.
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ItemForaging response of female bactrocera dorsalis (hendel) to a fruit fly protein food attractant([Honolulu] : [University of Hawaii at Manoa], [August 2013], 2013-08)Oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) causes serious economic loss for papaya (Carica papaya L.) production in Hawaiʻi through direct fruit damage and restriction of export commodities. Suppression of female flies was a challenge until a protein-based bait contains reduced risk insecticide spinosad became available, GF-120 NF Fruit Fly Bait (GF-120; Dow AgroScience, Indianapolis, IN). This bait provides an environmentally sound alternative to conventional cover spraysof organophosphate insecticides. Factors that influence the attractiveness of protein bait include chemical composition, visual stimuli, and competing volatiles from host fruits. This dissertation focuses on biological factors that affect the foraging response of female B. dorsalis to volatiles emitted by protein bait. Female reproductive state and dietary experience are two biological variables that shape the manner in which a fly searches for and responds to essential resources such as food and egg-laying sites. The experiments reported in this dissertation were conducted in order to assess the influence of physiological states on the response of female B. dorsalis to protein bait in papaya orchards. In Chapter 1, baseline information on key morphological characters in B. dorsalis ovarian development and the associated morphometric parameter of each oogenesis stage is collected. Four oogenesis stages include previtellogenesis, vitellogenesis, gravid and parous. In Chapter 2, field observations were conducted to determine reproductive states of B. dorsalis females (using ovarian developmental stage as an indicator) that respond to 2 two protein bait trapping devices: visually enhanced attract-and-kill bait stations termed papaya leaf mimics (PLMs) treated with GF-120 and dome traps containing torula yeast solution. Females with ovaries at previtellogenesis stage and egg laying females are the two main classes that responded to protein bait. Visual stimuli from the bait stations enhanced the response of immature females to protein bait but this effect was not found in egg-laying females. Yellow color also increased the capture of females with greater egg loads compared to those captured by green bait stations. This is an important finding for improved fruit fly management because reducing numbers of egg-laying females within an area results in lower fruit infestation. The physiological state of foraging flies determines the level of food searching behavior. In Chapter 3, the effects of female age and dietary history on the propensity of B. dorsalis to alight on protein bait were quantified. One week old females exposed to papaya as a diet source for 4 d in the first week of adult life showed a significantly greater propensity of alighting on GF-120 protein bait than females fed on a protein or sugar diet. Delay of ovarian development from feeding on a sugar only diet resulted in significantly higher response of 4 week old females to protein bait than females fed on papaya or protein. On the contrary, ovarian development in papaya fed females was not significantly different than that of protein fed females. Feeding on papaya during weeks 2 to 4 of adult life increased the response of female flies to protein bait at a lesser level than for 1 week old females. These results are evidence of the possible physiological profile of females attracted to protein bait in the natural environments. In addition, previous exposure to papaya fruit enhanced the response of females to papaya compared to females without the experience. This is a finding that suggests sanitation practice of removing culled fruit not only removes a breeding source but may also reduce the number of females re-entering orchards. Studies conducted in this dissertation are the first documentation of the response of egg-laying female B. dorsalis to protein bait under natural and semi-natural conditions. Results suggest that protein baits such as GF-120 attract females with developing ovaries as well as egg-laying females. In addition, fruit-based diet enhances the response of female B. dorsalis to protein bait and host fruit stimuli.
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ItemDeveloping a monitoring tool to understand the seasonal dynamics and management techniques to estimate a sampling plan for Xylosandrus compactus (Eichhoff) in Hawaiʻi([Honolulu] : [University of Hawaii at Manoa], [December 2010], 2010-12)The potential damage caused by the invasion of exotic ambrosia beetles to Hawaiʻi is one of the biggest concerns for the coffee, forestry and ornamental plant industries. Most of these invasive beetles are from temperate areas and find a suitable environment for reproduction and survival in Hawaii, which is favored by climatic conditions, presence of alternate hosts and the lack of natural enemies. The black twig borer, Xylosandrus compactus (Eichhoff), is an important coffee pest and native forests in Hawaiʻi. This ambrosia beetle is highly polyphagous, reported from >200 hosts, including native plants such as the valuable timber species Acacia koa. This dissertation addressed the response of X. compactus to semiochemicals which were used to determine the beetle flight seasonality, phenology of the black twig borer in coffee plantations, and development of a sequential sampling plan for management decision making. It was demonstrated that Japanese beetle traps baited with ethanol can serve as monitoring tool for the black twig borer, and ethyl alcohol baits yielded higher capture rates than eugenol and α-pinene. It was also demonstrated that the repellents verbenone and limonene, significantly reduced trap catches of black twig borer. Ethanol baited Japanese beetle tras were used to assess the seasonal fluctuation of black twig borer throughout the year. Data obtained from trapping demonstrated the peak beetle flight periods, which were used as an predictor of damage levels for accurate timing of control measures. Elevation and season were significantly related with the number of beetles captured and level of infestation. Taylor's Power Law analysis showed an aggregated infestation of X. compactus in coffee fields. The density of infested branches per sampled unit can be estimated using the sampling plan and compared with the action threshold level to make a management decision. Enumerative sampling allows estimation of the black twig borer abundance with specified precision, providing researchers with a valid tool for the study of this pest in coffee. Three species of scolytines were detected attacking coffee berries in Hawaiʻi, Xylosandrus compactus, Hypothenemus obscurus and H. hampei. The biology, behavior and management of these three species are discussed.