Thesis (Ph. D.)--Oklahoma State University, 2008. / Vita. Includes bibliographical references.

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The yellow fever and dengue fever carrying mosquito, Aedes aegypti, requires blood feeding for egg production. The blood proteins are digested in the midgut to yield amino acids which are the nutritional source for oogenesis. Serine proteases are important enzymes that participate in the process of blood protein digestion. The identification of the corresponding genes may have significant implications in the control of mosquito-borne diseases. A gut-specific chymotrypsin-like cDNA was isolated and sequenced. The 938 bp clone encodes a preproenzyme with a putative 18 amino acid signal peptide sequence, a 7 amino acid activation peptide sequence rich in serine and charged residues, and a mature enzyme of 268 amino acids. The deduced amino acid sequence has a typical catalytic triad region for serine proteases (His 57, Asp 102 and Ser 195 in bovine chymotrypsin numbering system), and the hydrophobic substrate binding pocket with most features of chymotrypsins. Six cysteine residues are present in the sequence which are characteristically involved in disulfide bond formation in invertebrate serine proteases. Characterization of the gene expression and the protein synthesis, as well as the enzymatic activity in the midgut, clearly demonstrated that (1) the chymotrypsin gene is newly transcribed after eclosion and the mRNA is present almost steadily during the digestion of a meal; (2) the chymotrypsin synthesis and its corresponding activity are induced and increased significantly by the ingestion of a meal. In vitro studies of the recombinant protease derived from the cDNA clone indicated several unique properties of the mosquito chymotrypsin compared with its bovine analog.

Three vitelline membrane (envelope) genes in Aedes aegypti mosquitoes were studied. A genomic clone corresponding to a novel vitelline membrane gene (15a-3) was isolated. The predicted peptide sequence of 15a-3 is similar to those of the A. aegypti vitelline membrane genes 15a-1 and 15a-2. The deduced amino acid sequences of 15a-1, 15a-2 and 15a-3 contain a conserved region of 45 residues. This region overlaps with a conserved region in four Drosophila melanogaster vitelline membrane genes. Genomic clones corresponding to 15a-1, 15a-2 and 15a-3 coding regions. A 360 bp region 5' of the 15a-2 coding region was identified with 72% identity to a region upstream of the A. aegypti VgA1 vitellogenin gene Sequences with similarity to a 20-hydroxyecdysone response element consensus sequence were found upstream of the three coding regions. The transcriptional regulation of three A. aegypt vitelline membrane genes was examined. The sites and timing of expression of the three transcripts were determined by Northern blot analysis and whole-mount in situ hybridization using mutually exclusive probes. The temporal pattern of 15a-1, 15a-2 and 15a-3 expression was similar. The spatial pattern of expression differed between the three genes. Only 15a-2 was expressed at the anterior region in addition to the remainder of the follicle. 15a-1 and 15a-3 wee only expressed in the mid and posterior regions of the follicle. Expression of 15a-1 was higher in ovaries that were dissected at intervals of 0, 2, 10 and 24 h after a blood meal and were cultured in medium containing 20-hydroxyecdysone, as compared to control incubations. In ovaries that were dissected at 36 h after a blood meal, incubation in 20-hydroxyecdysone had no effect on 15a-1 expression, as compared to control incubations.

<p> Most studies examining effects of extreme temperature on insect immunity have focused on negative impacts of high-temperature exposure. Although largely unexplored, a recent study suggests that repeated exposure to freezing temperature may enhance insects&rsquo; ability to survive microbial challenge. To determine if repeated low-temperature exposure impacts innate immunity of the goldenrod gall fly, <i>Eurosta solidaginis</i>, we counted hemocyte number, measured phenoloxidase activity and assessed antibacterial activity, and I examined up-regulation of immune-related genes in winter-acclimated larvae 24 h or 96 h after they were subjected to either zero (control), five, or ten diurnal exposures to -18&deg;C. To assess if time spent frozen, rather than freezing and thawing, influenced immunity, we also counted examined immune factors in larvae exposed to a single, six-day constant freeze. Repeated freezing negatively impacts hemocyte number, antimicrobial activity against Gram-negative bacteria, and had varied effects on phenoloxidase activity in the goldenrod gall fly. I suggest the effects of repeated cold exposure on insect immunity are governed by energy trade-offs and are not likely to mimic the effects of a single freeze.</p><p>

<p> <i>Arundo donax</i> is a rhizomatous perennial grass that invades riparian habitats and replaces native riparian vegetation. The galling wasp, <i> Tetramesa romana</i> (Hymenoptera: Eurytomidae), was selected for evaluation as a biocontrol agent of <i>A. donax</i> in 2009. However, knowledge is scarce on which factors influence host selection and oviposition in <i> T. romana.</i> Through my observations I documented distinct behavioral steps preceding emergence leading to oviposition in <i>T. romana,</i> and elicited an investigatory response in <i>T. romana</i> from plant volatiles extracted from <i>A. donax.</i> My results indicated that <i>T. romana</i> does use a chemical cue as a factor in host selection, but it is likely not the result of a species-specific constituent. Evidence from my study revealed that <i>T. romana</i> may use a physical cue in selecting a host as well. <i>T. romana</i> preferred round glass rods over flat glass slides, indicating that shape is an important factor in host acceptance.</p>

<p> Unregulated hunting and habitat loss led to a near extirpation of moose (Alces alces) in New Hampshire in the 1800s. After state protection in 1901, the estimated population increased slowly to &sim;500 moose in 1977, then increased rapidly in the next 2 decades to &sim;7500 following an increase in browse habitat created by spruce budworm (<i>Choristoneura fumiferana </i>) and related timber salvage operations, and then halved from 1998-2016 despite highly available optimal habitat. The declining population was partially related to the specific management objective to reduce moose-vehicle collisions, and a possible change in deer hunter and moose behavior that influence population estimates. But given the substantial decline in productivity and condition of cows, and frequent episodes of high calf mortality in April, the primary cause of decline was presumed to be is an increase in winter tick abundance. </p><p> This study examined the relationships among moose density, optimal habitat, weather/ground conditions, winter tick abundance, and natal dispersal in northern New England. Comparing movement data from the previous (2002-2006) and current (2014-2016) productivity studies in New Hampshire and Maine, the distance of natal dispersal, home and core range size, and home and core range overlap did not significantly (<i>P</i> > 0.05) change despite an increase in optimal habitat and a decrease in moose density.</p><p> Geographic changes in tick abundance were related to an interaction between moose density, and the onset and length of winter. Annual changes in tick abundance in northern New Hampshire are driven by desiccating late summer conditions, as well as the length of the fall questing season. Lower precipitation (6.4 cm) and higher minimum temperatures (9.8 &deg;C) specifically concentrated during larval quiescence from mid-August through mid-September reduces winter tick abundance and the likelihood of an epizootic event. The onset of winter, defined by the first snowfall event (> 2.54 cm), influenced the length of the questing season relative to the date of long-term first snowfall event (14 November). In the epizootic region, average winter tick abundance on moose harvested in mid-October indicated a threshold of 36.9 ticks, above which an epizootic is like to occur unless an early snowfall event shortened the fall questing season. Optimal habitat created by forest harvesting was produced at an annual rate of 1.3% (1999-2011) and is not considered limiting in northern New Hampshire, but likely concentrates moose density locally (&sim;4 moose/km²) facilitating the exchange of winter ticks. In northern New Hampshire, snow cover late into April did not reduce tick abundance in the following year and cold temperatures (&lt; 17 &deg;C) that induced replete adult female mortality are extremely rare in April.</p><p> Given a continuation of warming climate and conservative moose harvest weather conditions and high local moose densities will continue to favor the life cycle of winter ticks, increasing the frequency of winter tick epizootics and shift the epizootic region slowly northward. Conversely, temporary reduction of moose density may substantially reduce parasite abundance and support a healthier and more productive moose population.</p><p>

<p> Indirect interactions have increasingly been recognized as important forces influencing population dynamics and structuring communities. Associational susceptibility is a form of indirect effect in which a focal plant experiences greater herbivore damage due to neighboring plant identity or diversity. These interactions remain poorly understood in the context of invasion ecology, though they may be responsible for huge impacts of invasive species on native communities. This dissertation investigates the potential mechanisms and consequences of associational susceptibility of a native perennial shrub, <i> Atriplex canescens,</i> driven by an invasive annual forb, <i>Brassica tournefortii,</i> and an invasive herbivorous stinkbug, <i>Bagrada hilaris.</i> In Chapter 1, a potential associational effect is experimentally demonstrated and a phenologically-driven trait is identified as a potential mechanism for this interaction. In Chapter 2, relative host plant quality is explored for its role in mediating the numerical response of the shared herbivore, and the herbivore&rsquo;s damage impact on <i>A. canescens. </i> In Chapter 3, neighbor density, herbivore presence and herbivore density were manipulated to identify their impacts on spillover timing, extent, and fitness consequences for <i>A. canescens.</i> Overall, potential mechanisms of <i>A. canescens</i> associational susceptibility to <i> Br. tournefortii</i> and <i>Ba. hilaris</i> identified include: <i> Ba. hilaris</i> accumulation on <i>Br. tournefortii</i> followed by <i>Br. tournefortii</i> senescence and depletion, triggering <i> Ba. hilaris</i> alternative host-seeking. Associational susceptibility of <i>A. canescens</i> could not be re-created under experimental conditions, but further study is required to ascertain whether this interaction is due to experimental limitations or ecological implausibility.</p><p>

There is great interest in ecology to determine the drivers of species richness. For many taxa, and in natural circumstances, temperature is often found to be a good predictor of richness. The goal of this thesis was to determine, amongst several human-related and natural, environmental and ecological variables, the most important broad-scale predictors of butterfly species richness across Canada. Also, I presented a test of whether spatial relationships are adequate surrogates for the temporal relationship between richness and predictor variables. Using precisely georeferenced and dated butterfly records across Canada, I created butterfly species richness maps for two periods (1900-1930 and 1960-1990), and then related them to candidate predictors. Natural variables such as temperature, precipitation and soil type tended to explain most of the variance in species richness, while human-related variables such as habitat fragmentation, habitat heterogeneity and pesticide density added very little. A comparison of temporal and spatial relationships showed that temperature was a consistent predictor of richness through time and space, but that the impact of human activities on richness differed. My results are consistent with the species-energy hypothesis while showing that human-related variables are not having a large measurable effect on butterfly species richness patterns in Canada at broad scales. Also of critical importance in this thesis is the difference I found between the spatial and temporal relationships of richness vs. human activity level. I show that the assumption commonly made in macro-ecology that spatial variables are appropriate surrogates for temporal ones, is not always correct.

The tachinid fly Compsilura concinnata (Meigen) was introduced to North America in 1906 for the biocontrol of the forest defoliators Lymantria dispar (L.) and Euproctis chrysorrhea (L.) when these caterpillars were defoliating large areas of eastern Massachusetts. Most of the flies released, however, were the progeny of adults emerging from E. chrysorrhea caterpiliars collected in Eastern Europe. Although this tachinid is a generalist parasitoid, in Europe it is considered an important specialist of pestiferous species based on the level of its recovery there. Also, as one of the first insects established against forest defoliators in the Northeast, C. concinnata is in a premier position of providing information about colonization that increases the understanding in population genetics of how founder effects and dispersal influence the establishment of exotic insect populations. Initially in this study, a historical analysis was conducted to prepare a chronology of release of C. concinnata into North America and delimit its distribution. The introduction and release of C. concinnata was relatively restricted as they were primarily reared from one host E. chrysorrhea collected in Eastern Europe. More importantly, the extent to which this fly moved ahead of successive releases suggested there may be a historical basis to expect little differentiation among their nearctic populations. The literature on population genetics and use of electrophoretic analyses were surveyed to establish their use with C. concinnata in North America. Enzyme electrophoresis has been widely used for delimiting populations of non-native parasitoids and tracking their movement into new hosts and localities. To determine the suitability of enzyme electrophoresis for a population genetic analysis of C. concinnata, selected isozymes were identified and cataloged in an established laboratory strain. The analysis of isoenzyme patterns for measuring the relatedness among and between individuals, is useful in molecular studies of population genetics provided these patterns are heritable. To determine the heritablility of isozymes in C. concinnata, an electrophoretic analysis was conducted using both the parents and adult progeny of observed matings. The genetics of some C. concinnata isoenzymes followed simple patterns of Mendlian inheritance and were allozymic. The population genetic structure of C. concinnata in North America was examined with trap-hosts placed throughout the Northeast. The flies reared out were sampled with protein electrophoresis. There were slight differences in the allozymes and allele frequencies of C. concinnata and in comparison with other Diptera, the variation among Northeastern populations was relatively low. The variability among Northeastern populations of this parasitoid reflect limited genotypes in the founding populations. Over time new differences in protein loci between geographically separated populations probably arise through selection or drift than through non-lethal mutations. The time needed for protein coding loci between distantly spaced populations of introduced insects to diverge sufficiently for them to be detectable has not been determined. Estimating the time needed for allozymes of introduced insects to reject such differentiation is useful in understanding the evolution of biotypes, but is not a trivial process. Historical research in combination with analyses of the variability in allele frequencies among populations can be useful in determining the extent of divergence in non-native species that may lead toward new biologically adapted forms.