The housefly, Musca domestica, was used to test the short-term and long-term environmental effects of high population density. The first phase addresses the issue that there are two main selection forces that drive mating behavior, inter- and intrasexual selection. In intersexual selection the females are actively discriminating when choosing a mate and, thus, these male-female interactions are what predominantly define that population. However, in intrasexual selection, males potentially compete against each other over the pool of receptive females. I tested the hypothesis that a less complex courtship would be optimal in a high-density environment, short-term (i.e., one generation). Specifically, I videotaped the mating behavior of individuals subjected to one of two treatments: high-density or low-density (i.e., 200 virgin male-female pairs in a 2 L or 114 L cage, respectively). In both treatments, the flies were allowed to mate for 30 minutes while being videotaped. The proportion of time spent in three male courtship behaviors (HOLD, FORWARD, BUZZ) and one female courtship behavior (WINGOUT) were determined. I found that the mating propensity (percent of mated pairs) was significantly greater in the high-density environment. The courtships in the high-density environment were also significantly less complex (i.e., less FORWARD, less HOLD). My findings suggest that high-density environments stimulated competition among males causing the intrasexual selection processes to outweigh the intersexual processes. The second phase tests the prediction that long-term (i.e., eight generations), high population density will drive the evolution of courtship repertoire towards decreased complexity. I applied the previously outlined methods. Additionally, only those pairs that mated within the allotted time were allowed to contribute to the following generation. The courtship behavior assays suggest that the synergistic effects of high density on the males and inbreeding depression drove the evolution of increased courtship complexity and exaggerated inbreeding depression, therefore, not supporting the prediction or the results of first phase. In the low-density treatment, courtship became less complex and mating propensity increased. These results are applicable to populations with unnaturally high densities and potential for inbreeding such as those in laboratory agricultural pest control, and conservation projects.

The Drosophila melanogaster mutation bicaudal (bic) is the founding member of the group of maternal effect mutations that disrupt anterior-posterior axis formation by creating mirror image duplications of posterior segments in the anterior half of the embryo. The gene affected by the bic mutation was cloned, and a recessive embryonic lethal mutation, $vr22\sp{P3},$ was shown to be an allele of the same gene, demonstrating that the gene is essential. During embryogenesis, bic gene expression was detected in mesoderm and anterior and posterior midgut, and persistent expression was found in the somatic musculature. Late in embryogenesis, transcripts were detected in the central nervous system. The bic gene was shown to be expressed in two distinct locations in ovaries: transcripts were detected in somatic cells of the germarium, and a second activation of transcription was found exclusively in the germ-line derived nurse cells of ovarian follicles. The maternal effect of the bic mutation was shown to originate in failure to express transcripts of the gene in the germ-line nurse cells during oogenesis. The bic gene was found to encode the Drosophila homolog of beta NAC (Nascent polypeptide Associated Complex), a recently discovered ribosome associated protein of eukaryotes. Beta NAC is a subunit of a heterodimer that associates with nascent polypeptides as they emerge from the ribosome. In vitro, NAC regulates the specificity of co-translational targeting of nascent chains to the Endoplasmic Reticulum. The studies of the bic mutant effects presented here demonstrated that beta NAC has other unpredicted ribosome-associated functions, being required to ensure localized expression of proteins via translational control of mRNA. In oocytes/embryos of bic mutant females, negative regulation of translation of the mRNA of nanos, the posterior determinant, fails; NANOS protein is aberrantly expressed in the anterior compartment of the early embryo, and consequently, bicaudal embryos are created. Negative regulation of nanos was thus shown to include ribosome associated events. Furthermore, these first in vivo studies of the activity of beta NAC (BIC) identified a new ribosome associated function for the protein, and established a physiologically relevant and informative molecular genetic model system for future studies of NAC.

Social insect workers often sacrifice their own reproduction so that they may help relatives to reproduce more successfully. However, genetically dissimilar colony-mates may prefer to aid different kin, and this may result in disruptive conflicts. I developed polymorphic microsatellite genetic loci for the African swarm-founding wasp Polybioides tabidus to examine mechanisms to reduce such conflicts. Swarm-founding wasps have many reproductive queens in their colonies which should lower relatedness, increasing the potential for conflicts. I found that even though P. tabidus colonies contained many queens, relatedness was elevated because new queens were only produced after the number of old queens had been reduced to one, or nearly one. Queens were thus highly related, elevating relatedness in the colony as a whole, and promoting sociality. This unique pattern of queen production is consistent with a worker manipulation of the sex ratios known as cyclical oligogyny. Under cyclical oligogyny, new queens are produced when the colony has few queens, while males are produced when the colony has many queens. The males were indeed produced when queen number was higher, and I found evidence that the workers collectively controlled male production. Colonies which produced normal haploid males also produced diploid males, which have a diploid genome but are homozygous at the sex determining locus. P. tabidus does not appear to effectively distinguish between diploid and haploid males, and diploid males should have occurred in colonies without haploid males too. Their absence indicates that they were actively eliminated from colonies in which the workers did not favor male production. Workers also may have controlled who produced the males. Each worker should prefer to produce the males herself. However, I found that the queens produced the males. This may be explained by collective worker policing because the workers would be more highly related to queen-derived males than to the sons of other workers and should prevent reproduction by other workers. Alternatively, each worker might restrain herself if worker reproduction was costly to the success of the colony. The results of this study indicate that collective worker control is an important mechanism stabilizing cooperation.

pushover (push) is a mutation that causes neuronal hyperexcitability, uncoordination and male sterility. Here it is also shown that push mutant wandering third instar larvae exhibit segmental nerves that are slightly thickened compared to wild type controls. The additional thickness of these nerves is due to a thicker perineural glia layer surrounding the axon bundle of the nerve. From investigation of push mutant testes, it was determined that mature sperm are produced, but are immotile. The push gene was cloned and sequenced and encodes a 5322 amino acid protein with 12 putative transmembrane helices. Sequencing of the push gene in the push 1 mutant line revealed a premature stop codon at amino acid position 728 and in push2 a premature stop codon at position 883. In situ hybridization experiments show push is expressed in the embryonic CNS and in primary spermatocytes in the adult testes and suggest that push is not expressed in the perineural glia of wandering third instar larvae. Because push affects but is not expressed in these glia, it is hypothesized that push is involved in a signaling pathway connecting the motor neuron to the perineural glia.

Although social hymenopteran colonies show a high level of cooperation among their members, colony members can have conflicts among themselves as well. One of these intra-colonial conflicts is who produces the males. I studied the resolution of conflict in stingless bees, a species-rich group with a tropical distribution. In the majority of stingless bee species both workers and queens are able to produce males. Therefore intracolonial conflict over male production is predicted. Because stingless bee queens mate only once, workers are more related to their own and to each other's sons than to the sons of the queen. Thus on genetic grounds, worker production of males is expected. However, workers might not reproduce if the costs of reproduction are high, or if the queen is able to suppress workers. The decision could have been made in the bygone times and the current pattern does not serve adaptive functions at the present. To test my predictions of conflict over male production I looked at three levels: within colonies, within species, and between species. On the colony and species level, I hypothesized that current conflict is expressed by behavioral antagonism between the workers and their queen. Furthermore, I predicted behavioral conflict to be higher in the periods when males are produced compared to periods with only female production. On the level of comparison between species I expected more signs of conflict in species where both workers and queen produce males than in species where males are all queen derived. The conclusions of this study concerning conflict over male production in stingless bees are: (1) Genetic tools confirmed that workers reproduce in some, but not in other species. (2) The costs involved with worker reproduction could explain why in some species workers reproduce and in others not. (3) There is not only a variance of worker reproduction between, but also within species. Demographical factors might be essential determining the amount of worker reproduction within species. (4) The pattern of worker reproduction could be explained by costs although phylogenetic relationships could explain the pattern also.

<p> The rice stink bug, <i>Oebalus pugnax</i>(F.), is an important late season pest of rice that is noted for causing grain yield and quality reductions in the United States. This study investigated rice injury using field cages in two rice cultivars ('Cocodrie' and 'Wells') at bloom, milk, and soft dough stages and <i>O. pugnax</i> ecology in the Delta Region of Mississippi. </p><p> Specific objectives were: 1) to determine the impact of adult <i> O. pugnax</i> infestation on rice yield and grain quality at bloom, milk, and soft dough stages of rice development; 2) to determine the impact of adult <i> O. pugnax</i> gender and infestation duration on rice yield and grain quality at the milk stage of panicle development; 3) to identify and examine the seasonal abundance and phenology of <i>O. pugnax</i>on non-cultivated host grasses; and 4) to evaluate feeding preference and development of <i> O. pugnax</i> on host grasses. </p><p> Rice injury increased as <i>O. pugnax</i> density increased. The bloom and milk stages were the most vulnerable to blank and discolored kernels, respectively. <i>O. pugnax</i> feeding injury was significant after 3 d of infestation duration during the milk stage of panicle development. Female <i>O. pugnax</i> caused a greater percentage of blank kernels compared to males. </p><p> A survey of <i>O. pugnax</i> hosts indicated that Italian ryegrass, <i> Lolium perenne</i> L. ssp. <i>multiflorum</i> and winter wheat, <i> Triticum aestivum</i> L., were important hosts during spring and early summer. Junglerice, <i>Echinochloa colona</i> (L.) Link; crabgrass spp., <i>Digitaria</i> spp. Haller; southwestern cupgrass, <i> Eriochloa acuminata</i> (J. Presl) Kunth; and praire cupgrass, <i> Eriochloa contracta</i> (Hitchc.), were important hosts for <i> O. pugnax</i> during early to mid-summer. Browntop millet, <i>Urochloa ramosa</i>, and broadleaf signalgrass, <i>Urochloa platyphylla</i>, supported adult <i>O. pugnax</i> prior to overwintering. In a choice test of wild host grasses, junglerice was the most preferred over 10 other host grasses. In the no-choice test, mean development time was shorter and survival was greater for <i>O. pugnax</i> nymphs reared on rice, <i> Oryza sativa</i> L., compared to dallisgrass, <i>Paspalum dilatatum </i> Poir and junglerice. These results provide biological and ecological information on which new <i>O. pugnax</i> integrated pest management practices can be developed.</p>

<p> Various models of density dependence predicted different evolutionary outcomes for <i>Helicoverpa zea, Diabrotica virgifera,</i> and <i> Ostrinia nubilalis</i> using simple and complex resistance evolution models, different dose assumptions and refuge proportions. Increasing available refuge increased durabilities of pyramided Plant-Incorporated-Protectants (PIPs), especially between 1&ndash;5%. For some models of density dependence and pests, additional refuge resulted in faster adaptation rates. Significant considerations should be given to a pest's intra-specific competition in simple and complex theoretical models when designing insect resistance management plans. </p><p> Life-history, refuge, and dose characteristics of a PIP had different effects on the adaptation rate of a generic pest of Bt, and unexpected outcomes occurred. Intrinsic growth rate 'R₀' was the strongest evolutionary force, and large R₀'s reduced time to resistance for a high dose PIP to similar levels as projected for a low dose PIP. This was caused by differential density dependent effects in refuge and Bt fields that elevated generational resistance increases beyond those from selection alone. Interactions between density dependence and R₀ were always present and further affected the life-time of the PIPs. Varying 'average dispersal distance' did not affect evolutionary outcomes; however, increasing the proportion of the population engaging in dispersal often increased the durability of high dose PIPs. When resistance genes spread from a hypothetical hotspot, local resistance phenomena developed in the immediate surroundings. Higher growth rates lead resistance to spread faster through the landscape than lower rates. Increasing available refuges slowed adaptation rates to single PIPs and low dose pyramids, although non-linear trends were possible. </p><p> Integrated Pest Management (IPM) practices at the onset of PIP commercialization slowed pest adaptation rates. For corn rootworm, interspersing non-selective periods with IPM+IRM delayed resistance evolution, yet crop rotation was the best strategy to delay resistance. For bollworm inclusion of isoline corn as an IPM tool did not increase the life-time of the PIP. A local resistance phenomenon for rootworm was maintained immediately surrounding the hotspot; random selection of mitigatory strategies in the landscape slowed adaptation rates while mitigation in the hotspot alone did not. Mitigation extended the life-time of the pyramid minimally for both corn rootworm and bollworm.</p>

<p> Every interaction between species occurs in a heterogeneous environment that presents countless contexts that shape the interaction over time and space. The consequences of these interactions can regulate populations, as they trickle down to influence the genes that an individual passes on to its offspring, and then, in turn, scale back up to influence the genetic and phenotypic composition of future populations. In this work, I sought to uncover how these principles play out in the interactions between an invertebrate vector of human disease and the disease agent it carries. Disease vectors are often considered in a context that is faithful to the word as it is used in physics, where the vector is viewed as public transportation that moves the pathogen between hosts, experiencing no consequences of parasite infection. However, vectors face the challenge of how to maximize individual fitness in a stochastic environment with limited resources just as all other species do, so why would they be exempt from the effects of being parasitized? As such, I investigated the triatomine bug species <i>Rhodnius prolixus</i> when infected with the parasite <i>Trypanosoma cruzi</i> (etiological agent of Chagas disease), and co-infected with <i>T. cruzi</i> and its sister species, <i>T. rangeli.</i> I asked, does <i>T. cruzi</i> affect <i>R. prolixus</i> fitness, and under what contexts does this effect vary? I found a large range of variation in <i> R. prolixus</i> fitness when infected with <i>T. cruzi,</i> with the outcome being influenced by parasite strain, co-infection with <i> T. rangeli,</i> parasite dose, and the timing and order of infection. These factors did not act alone, but seemed to be dependent on one another: it was better to have a co-infection at lower <i>T. rangeli</i> doses, but at high <i>T. rangeli</i> doses, it was better to be infected with <i>T. cruzi</i> first, suggesting an interaction between dose, order and timing. These results illustrate the interactions across scales of both biological and spatio-temporal complexity that can be revealed when studying infectious disease through an ecological lens. Moreover, this work emphasizes the importance of taking into account the ecology of vector-borne neglected tropical diseases such as Chagas disease.</p>

<p> Alkali bees, <i>Nomia melanderi</i>, are native, solitary, soil&ndash;nesting bees commercially managed in southeastern Washington State. They nest in dense aggregations and are important pollinators of alfalfa produced for seed. The Washington State Department of Transportation (WSDOT) proposed safety improvements to US Highway 12 through the Touchet&ndash; Lowden&ndash;Gardena alfalfa seed growing district, an area critical to alfalfa seed production. This includes northern realignment to accommodate a wider roadway and avoid impacting any towns. Relocation of the highway will bisect several <i> N. melanderi</i> nesting aggregations and alfalfa fields. The study has three objectives: 1) survey the population abundance of <i>N. melanderi </i> across the region by comparing two sampling techniques; 2) determine bee flight heights across roads; and 3) determine <i>N. melanderi</i> foraging range using transgenic pollen. </p><p> Regression was significant between the two population sampling methods. Mean emergence hole counts, mean prepupal counts, and the surface area of the nesting aggregations, were used to estimate the abundance of<i> N. melanderi</i> in each bee bed. We constructed a &ldquo;vehicular bee sweeper&rdquo; designed to capture insects at specific heights over the roadway. The majority of <i>N. melanderi</i> flew below 2.1 m when no other factors were considered, but environmental conditions like temperature and wind speed affected number and flight height of <i>N. melanderi</i>. To determine <i>N. melanderi</i> foraging distance, adults were collected from their nest sites, and pollen on their hind tibia was tested for the presence or absence of Roundup&ndash;^&reg;Ready alfalfa (RRA). The minimum foraging distance was 0.04 km and the maximum was 4.62 km. These distances suggest that <i>N. melanderi</i> will cross the highway for floral resources, increasing potential mortality. </p><p> Studying <i>N. melanderi</i> population abundance and flight characteristics allows us to understand the potential impacts of the proposed highway on bee populations and on alfalfa seed producers. The non&ndash;destructive quadrat method of sampling <i>N. melanderi</i> populations is robust compared to the destructive, labor-intensive, soil core method. Due to the low-flying nature and foraging distance of <i>N. melanderi</i>, vehicle strikes can be expected to cause mortality in bisected populations. Ultimately, recommendations will be made to highway designers to minimize and mitigate these effects. &#8195;</p>

<p> Recent research has revealed a trend of decreasing pollinator abundance and diversity in regions throughout the world. This highlights the need to understand factors influencing patterns in bee community structure and the drivers of bee diversity and abundance patterns. My dissertation uses several methods to determine factors structuring bee communities with regards to diversity and abundance. I selected 10 sites in different regions of the Central Valley of California that differ with regards to land use and floral diversity. Bee communities at each site were sampled for diversity, abundance, and bee-floral host relationships. </p><p> Sampling bee communities is often done using only bee bowls because netting is time consuming and prone to sampler bias. In chapter one the methods used in this study were detailed and the use of bee bowls and netting in capturing a representative sample of the bee community were compared using the S&oslash;rensen's similarity index and the Bray-Curtis dissimilarity index. It was determined that sampling using one method alone would miss approximately 40% of the species richness of the community. Further, there were biases in using bee bowls and nets; the bee bowls sampled certain species more than nets and vice versa. This chapter provides evidence that to adequately sample a bee community both bee bowls and netting must be used. </p><p> Chapter two focuses on bee biodiversity and the correlation between bee species richness and plant diversity. Patterns of diversity in bee communities of the Central Valley indicate that the family Apidae was more speciose than other families. However, on a species level, those from the family Halictidae far exceeded species from Apidae in abundance. This could have reflected a sampling bias given that pan traps tend to sample individual bees from Halictidae more than Apidae. Chapter two also focused on temporal variability. There was considerable temporal variability in the abundance of one of the more abundant species, <i>Lasioglossum incompletum.</i> This highlighted the need for studies of longer duration in order to account for natural stochasticity in bee populations. Several different diversity indices were used to assess the biodiversity of the different study locations; Putah Creek sites were found to be more diverse than the San Joaquin sites. A correlation analysis was used to determine that a positive relationship between plant diversity and bee species richness did exist for 2005 but not 2006. This indicated that plant diversity may be one of the factors driving bee species richness and community structure. </p><p> Another factor possibly accounting for variation in bee species richness and abundance is land use. Chapter three used non-metric multidimensional scaling and generalized linear mixed effects model to test for associations between differences in land use patterns and bee species richness and abundance. While there was no direct association between these factors, the ordination did show that the Putah Creek sites, San Joaquin sites, and Cosumnes sites clustered together. Therefore, sites that shared similar land-use patterns were related along a gradient. These cluster patterns were used to group the study locations for the other analyses performed in this project. The Putah Creek sites were characterized by agriculture and urban land use whereas, San Joaquin was semi-natural and Cosumnes Preserve was semi-natural and agricultural. </p><p> Chapter four is an analysis of the pollinator networks of Putah Creek, San Joaquin, and the Cosumnes Preserve. Pollination webs, matrices, and gplots were used to visualize the networks, while network and species-level indices were used to assess asymmetry, specialization versus generalization, and connectance. It was determined through these analyses that the connectance of the network decreased with increasing species richness and the complexity and composition of the network varied between the three regions of the Central Valley. Further, the San Joaquin Refuge sites, which were characterized as seminatural land use, contained a higher number of oligolectic species than other sites dominated by agricultural and urban land use. </p><p> The focus of this project was to use different methods to determine drivers of bee species diversity and abundance in different bee communities of the Central Valley of California. Three conclusions can be drawn from the analyses presented; 1) Given temporal variability in bee populations, studies of longer duration must be conducted to determine factors affecting bee community structure from that of natural population variability, 2) Floral diversity is positively correlated with bee species diversity and abundance but it is not the only factor influencing bee community structure. and 3) Land use change may be a factor influencing bee-plant networks but studies that compare networks across space and time are needed to determine the nature of this relationship. </p>