No description available.

published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

No description available.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 120-137).

A statistically sound and quantifiable bioassay procedure was developed for determining the response of adult Delia radicum to oviposition stimulants. The method was based on the use of surrogate leaves coated with test compounds. All of the test compounds were of purity 99% or greater. Twelve of the tested compounds were synthesised the remaining twenty four were either donated or available commercially. Attempts to follow literature methods to synthesise glucosinolates were unsatisfactory and an investigation of the procedures led to a number of synthetic modifications. Despite various attempts, the failure to sulphate a thiohydroximate to produce a glucosinolate was not resolved. Attempts to correlate oviposition stimulus with chemical structure produced a very significant finding. The results showed that a wide variety of chemically dissimilar compounds were effective stimulants providing they contained an S=O group. Thus sulphoxides, sulphones, sulphinic, sulphonic acids and their derivatives were all effective. Thiols and thioethers were non-stimulant, as were naturally occurring glucosinolates which had been chemically modified by the removal of the oxime sulphate group. The relative effectiveness of the oviposition stimulants was examined by determining the number of eggs laid on surrogate leaves relative to a prop-2-enylglucosinolate (sinigrin) standard over a range or concentrations. Statistical modelling of the data collected produced a maximum relative number of eggs laid (YMAX) at an optimum concentration (C) for each compound. It was not found possible to produce a single parameter combining YMAX and C, neither did any other structure-activity feature emerge from the study.

Thesis (M.Sc.) - Carleton University, 2003. / Includes bibliographical references (p. 98-106). Also available in electronic format on the Internet.

No description available.

<p>  </p> <p>Plant chemistry influences plant-nutritional quality, which in turn impacts plant-insect interactions. Plant secondary metabolites are pervasive in the plant kingdom and have been shown to influence both plant nutritional quality and plant-insect interactions. Levels of these secondary metabolites, as well as quantity, can impact availability of key macromolecules herbivorous insects need for optimal nutrient intake. Herbivorous insects can modulate their growth, rate of consumption, and frass production in response to diet with poor nutritional quality. Insects can also increase the production or activity of nutritional and detoxification enzymes to offset diet with poor nutritional quality. While the influence of plant secondary metabolites on nutrient intake is better understood in many plant systems, it is not well understood in plant-insect interactions involving <em>Cannabis sativa</em>. An increase in large-scale agricultural production of <em>Cannabis</em> has introduced a novel secondary metabolite, cannabinoids, a terpenophenolic compound with known physiological effects in many animal systems, onto the landscape. While insects have been shown to exhibit reduced performance on higher cannabinoid diets, insects lack human-analog cannabinoid receptors, so how these compounds interact with insect herbivores is not well understood. A goal of this study was to increase the understanding of how cannabinoids influence herbivorous insect performance. </p> <p>To understand the influence of cannabinoids on insect performance and enzyme activity I performed no-choice feeding bioassays on fall armyworm (<em>Spodoptera frugiperda</em>) with artificial diet spiked with different concentrations of cannabidiol (CBD). I measured growth, consumption, and frass production. From these same larvae, I also analyzed detoxification and nutritional enzyme activities. I found that as CBD concentration increased in diet, growth and consumption of fall armyworm decreased. I also found that as CBD concentrations increased, protease and cytochrome P450 enzyme activity decreased, and β-glucosidase enzyme activity increased. These outcomes highlight potential mechanisms for both behavioral and biochemical mechanism by which CBD confers resistance to insect herbivores.</p> <p>As agricultural production of <em>Cannabis</em> continues to increase, cannabinoids will continue to alter the chemical landscape of agricultural systems. How insect herbivores contend with cannabinoids is an important step in understanding plant-insect interactions in <em>Cannabis </em>systems. Identification of the structural and functional characteristics of protease and cytochrome P450 enzymes influenced by cannabinoids are possible future avenues of research that can better develop our understanding of <em>Cannabis</em>-insect interactions.</p>

Mosquito phytophagy is a critical component of mosquito biology, contributing to their survival, flight activity and reproductive output and thus fueling their role as deadly vectors of disease. To alleviate the issues faced by current control methods, such as increased insecticide resistance and environmental damage, novel control strategies have emerged that exploit the mosquito's biological need to feed on sugar. However, an improved understanding of sugar feeding behavior is needed to better optimize these strategies. Here, we determined the prevalence of mosquito sugar feeding on ornamental plants and wildflowers by using DNA barcoding on mosquitoes captured in residential Blacksburg, VA, and identified their preferences for commonly planted flower species. Based on this information, we then confirmed the rate of sugar feeding on the attractive flower goldenrod (Solidago spp.) in the wild and explored its attractive qualities with the intent of developing a novel, ecologically friendly attractant. Similarly, we observed the sugar feeding behavior of invasive species Aedes japonicus on the toxic native flower fly poison and assessed its suitability as a naturally sourced attractant and toxin for use in attractive toxic sugar baits. Finally, we compared the morphology, metabolism and life history traits of mosquito species with unique host preferences. This work expands our knowledge on mosquito phytophagy and contributes to the development of new, highly needed control strategies. / Doctor of Philosophy / Mosquitoes are considered by many to be a blood-feeding nuisance and a vector of disease. While it is true that the females of several species need blood to develop their eggs and transmit disease-causing pathogens through blood feeding, mosquitoes need to frequently feed on plant-derived sugars to survive in the wild. In fact, male mosquitoes feed exclusively on sugar and both sexes use sugar as an energy source for flight. Because sugar feeding is such a critical component of mosquito biology, many novel disease vector control strategies have recently emerged that exploit this behavior, making it important to study. However, there is much that remains to be understood about their plant preferences and how they find these preferred plants in the wild. Here, we used new molecular techniques to determine what plant species mosquitoes commonly feed on in residential areas of Blacksburg, VA. We then explored the attractive qualities of goldenrod, a plant fed on frequently by mosquitoes in Montgomery County, VA. We also examined whether an invasive species, Aedes japonicus, can feed on the native toxic flower fly poison and analyzed the effect of sugar concentration on the metabolism, survival and egg-laying rate of two important invasive disease vectors: Aedes aegypti and Culex quinquefasciatus. The results found here improve our understanding of mosquito sugar feeding and have applications for the development of new disease control techniques.

I used a data-set of 986 plant species (from 493 genera in 195 families) obtained from a literature search and a new data collection for 58 tropical tree species (from 31 genera in 18 families) growing in two contrasting forest types in Brunei Darussalam: mixed dipterocarp forest on moderately infertile ultisols and fluvisols, and heath forest on acidic and nutrient-poor spodosols.  I provide statistical evidence for the existence of discreet groups of species representing Al accumulators and non-Al accumulator based on foliar Al concentrations.  The threshold foliar Al concentration was higher for tropical plants (range 2.3-3.9 mg Al g^-1) than temperate plant (1.1 mg Al g^-1). Species’ mean log foliar Al concentration was also higher for tropical (0.73 ± 1.11 mg Al g^-1) than temperate plants (0.16 ± 1.07 mg Al g^-1).  I used the tropical Al accumulating shrub <i>Melastoma malabathricum </i>L. as a study species to test the hypotheses that growth would be stimulated by Al addition.  Growth of <i>M. malabathricum </i>seedlings was stimulated by Al addition when the external supply of macronutrients was very low, and this growth response was associated with an increase in net assimilation rate and specific leaf area.  Foliar Al concentration was positively correlated with foliar concentrations of Ca and Mg across 16 Al accumulator species sampled in the field study in Brunei Darussalam, while foliar Al and K concentrations were correlated positively in <i>M. malabathricum </i>seedlings growing in the solution culture experiments.  These positive correlations contradict the hypothesis that Al inhibits the uptake of nutrient cations and they may contribute to the positive growth response to Al addition in Al accumulator plants.