The planthopper Prokelisia marginata is the most common insect herbivore in the salt marshes of northwestern Florida, where it feeds and reproduces on smooth cordgrass, Spartina alterniflora Loisel. Relative to other sites where it has been studied, population densities of this planthopper in north Florida are low, despite high fecundity. Low nymphal survivorship, combined with high rates of adult mortality and dispersal, rapidly diminish the densities of local populations. Many factors act to alter the dynamics of planthopper populations. This study was designed to determine the magnitude of the effect of several of these factors on the demography and population dynamics of Prokelisia marginata at Apalachee Bay, Florida. / A field experiment looked at the impact of tides on planthopper populations. Artificial islands were used to create patches of the host plant. Floating islands were used to eliminate tidal inundation and waves, while populations on other islands experienced natural tidal conditions. Analysis showed that the populations did not differ significantly in size throughout the experiment and that they had similar dynamics. In the laboratory, simulated tidal inundation experiments showed that Prokelisia marginata is behaviorally adapted to withstand tidal submergence, either by retreating from the tide or by becoming submerged, and that the planthoppers are able to survive long periods under water. / A second field experiment examined the effects of spider predation on populations of Prokelisia marginata. Nymphal populations were significantly reduced in the presence of spiders, but adults were unaffected. Thus, spider predation had no effect on the population as a whole. A laboratory experiment showed that nymphs are more susceptible than adults to direct predation, and that the presence of spiders alters their life history. / The most important factor acting to reduce adult densities appears to be dispersal of the insects away from their populations. Because most of the dispersing insects probably fail to locate new sites on which to reproduce, dispersal is an important factor acting to reduce populations of Prokelisia marginata in northwestern Florida. / Source: Dissertation Abstracts International, Volume: 50-12, Section: B, page: 5443. / Major Professor: Donald R. Strong. / Thesis (Ph.D.)--The Florida State University, 1989.

The biology and foraging behavior of the fairyfly parasitoid Anagrus delicatus (Hymenoptera: Mymaridae) were studied to determine their effect on host population dynamics and stability. Anagrus delicatus is a short-lived solitary parasitoid that attacks the egg stage of two geographically sympatric planthoppers, Prokelisia marginata and P. dolus (Homoptera: Delphacidae). Host eggs are laid within the leaves of the grass, Spartina alterniflora, found in salt-marshes of the Atlantic and Gulf coasts of the eastern United States. / Laboratory studies indicate that upon locating a patch (S. alterniflora leaves), A. delicatus quickly and efficiently detects the presence of host eggs. Wasps remain on a patch for up to ten hours, but numbers of hosts attacked are low and variable and not much affected by host density. This low attack rate is not a consequence of differences among host species, parasitoid egg limitation, long handling times, a high ratio of parasitized to unparasitized hosts, or the presence of a host refuge. However, direct interference among parasitoids does cause a decrease in number of attacks as wasp density per patch increases. These behaviors lead to density-independent parasitism among S. alterniflora leaves. / Field studies that measured the response of natural populations of A. delicatus to experimental host patches corroborate these laboratory findings. Per capita numbers of hosts parasitized are low, variable, and a declining function of parasitoid density (parasitoid interference); and result in spatial and temporal density independence. Wasps appear to favor a foraging strategy that serves to spread eggs among a number of host patches. / I examined these parasitoid behaviors for their effect on stability in traditional host-parasitoid models. In general, patch use by A. delicatus is not stabilizing, but parasitoid interference can greatly enhance or cause interaction stability. A model developed specifically for this system that incorporates both host and parasitoid biology and behavior supports this conclusion. Due to parasitoid interference and asynchrony in host and parasitoid generation times, this model predicts that A. delicatus will cause the host population to exhibit "stable" cycles through time; exactly the pattern found in nature. / Source: Dissertation Abstracts International, Volume: 52-10, Section: B, page: 5069. / Major Professor: Joseph Travis. / Thesis (Ph.D.)--The Florida State University, 1991.

Insects exhibit considerable variety in their morphology and can be found in many diverse habitats. Despite these variations, early neurogenesis seems to be conserved in insects. In all species investigated to date it begins with the formation of neural stem cells (neuroblasts), which establish a distinct internal layer and produce a fixed number of neurons and glial cells. The neuronal cells then form a characteristic rope ladder-like axonal scaffold. However, it is evident that the composition or identity of the individual neurons must have changed during insect evolution to allow for variations in neuronal networks. This raises questions regarding which developmental steps have been changed and the manner in which they have been modified. In order to address these questions, early neurogenesis was analysed in the flour beetle Tribolium castaneum and the results were compared to the well-studied fruit fly Drosophila melanogaster. Initially a map of trunk neuroblasts in T. castaneum was established, which revealed a high degree of conservation in the arrangement of individual neuroblasts compared to D. melanogaster. However, a comparison of the expression patterns of genes that confer regional identity to neuroblasts showed considerable variations. Significant differences in the expression patterns of the segment polarity gene wingless and the columnar gene ventral nerve cord defective (vnd) were found. Furthermore, the impact these changes in neuroblast identity have on the composition and identity of their respective progeny was analysed. As a result changes in the number of Even-skipped and Tailup expressing neurons in T. castaneum embryos were found, with three-fold more Tailup expressing neurons compared to D. melanogaster. To further analyse the role of the neuroblast identity gene vnd in the formation of Even-skipped positive neurons, RNAi gene silencing studies were performed, resulting in the loss of neurons and changes in neuronal migration pattern. In summary, the results demonstrate that evolutionary changes in neuronal networks result from changes in neuroblast identity, which in turn have an impact on the composition of neuronal lineages.

In the present study, I demonstrated the ability of the xylem-feeding leafhopper, Carneocephala floridana, to discriminate between differentially fertilized Spartina alterniflora, which possessed varying levels of foliar nitrogen content. The hopper was capable of detecting, and preferentially fed upon, minimally fertilized plants, which did not differ in percent of foliar nitrogen from unfertilized control plants. / Chemical analyses of the xylem sap and performance data from another host plant, Borrichia frutescens, confirmed that amino acid levels in highly fertilized plants become very unbalanced and are either unusable, or toxic, to C. floridana. Highly fertilized plants had elevated levels of NH$\sb4\sp+$, and a nitrogen content, that is probably well above those found in naturally occurring B. frutescens. These results suggested that a threshold detection mechanism may be operating. C. floridana's host plants show seasonal trends in their nitrogen content. While, the field patterns of C. floridana did not suggest that the hopper switches host plants based solely on interspecific nitrogen content; intraspecific nitrogen content did show several trends that were consistent host plant usage. My results suggest that the spatial and temporal distribution natural populations of C. floridana may be influenced by host plant nitrogen, but crude nitrogen is not a good predictor of interspecific host plant preference. / In addition, egg mortality and parasitism rates were also higher on the grasses compared to the herbaceous species. It appears that host plant water content may be largely responsible for plant mediated egg mortality. In addition, high parasitism rates on the two grass species may be related to the orientation of eggs, which are laid in parallel packets just below the surface of the epidermis. Conversely, eggs laid on the two herbaceous species appear to be less accessible to searching parasitoids. / My data suggest that Carneocephala floridana should utilize the two grasses only when the two herbaceous species are unavailable. In the salt marshes of Florida's northern Gulf coast, this occurs during the winter when the herbaceous species experience a substantial dieback. / Source: Dissertation Abstracts International, Volume: 52-08, Section: B, page: 4007. / Major Professor: Donald R. Strong. / Thesis (Ph.D.)--The Florida State University, 1991.

Lipoproteins, protein-lipid complexes that have a polar exterior and a non-polar interior, have been found in many vertebrate and insect species, and their basic structure and function appear to be conserved. They facilitate the intercellular transport of hydrophobic lipids through aqueous media. Their synthesis requires an unusual process referred to as lipidation, whereby lipids are added to the protein component of the lipoprotein. Lipidation is thought to occur during or immediately following translation of these proteins, but how this process occurs is unknown. Of particular interest is the extent to which the protein sequence of the apoproteins drives lipidation and the level of involvement of other proteins in this process. In this project, lipidation was studied by expressing the apolipoproteins from the tobacco hornworm, Manduca sexta, in two different expression systems. The first used budding yeast, Saccharomyces cerevisiae , to both determine the ability of unicellular organisms to produce lipoproteins and examine the role that the known secretory pathway for soluble proteins plays in lipoprotein biosynthesis. The second used Drosophila Schneider 2 cells to begin to examine the apolipoprotein sequence for regions that are crucial to lipoprotein biosynthesis. The yeast expression system revealed that unicellular organisms are capable of expressing, lipidating, and secreting M. sexta apolipoproteins. This is first demonstration of any apolipoprotein being expressed in a unicellular organism, and represents a major finding, as unicellular organisms have no need for a particle that functions in intercellular transport. A second major finding in this project is that lipophorin production occurs in the absence of the full apoLp-I sequence. This finding was true for both expression systems, and indicates that the lipidation code resides within the first 45% of the precursor protein sequence. Furthermore, deletion analysis has revealed that removal of any portion of the apoLp-II sequence prevents expression of the apolipoprotein. Taken together, these experiments indicate that all of the information required to make a lipoprotein is included in the apoLp-II sequence.

Choosing where offspring will develop is especially important for insects whose larval stages are restricted to a particular host resource. In such insects, maternal egg laying decisions may not only involve choosing optimal hosts based on their intrinsic qualities but also avoiding hosts occupied by conspecific brood. The ability to discriminate between previously exploited and unexploited hosts is often mediated by the use of a marking pheromone. Despite engaging in what appears to be host-marking behavior, the walnut fly Rhagoletis juglandis prefers to deposit clutches into previously exploited hosts. In this dissertation, I quantified host reuse in R. juglandis and assessed its impacts on offspring fitness. I also explored the role that marking pheromone plays in level of reuse. Host reuse by the walnut fly was common in the field, where trees were synchronously infested over a 14-17 day period. It was not unusual for individual fruit to bear 40-80 eggs; given that females laid clutches of ca. 16 eggs, each oviposition puncture probably contained ca. 1.6 clutches. The overall number of eggs deposited into fruit was positively correlated with fruit volume. Field and laboratory experiments showed that increases in larval densities within fruit reduced larval survival and pupal weight, the latter being strongly correlated with the number of eggs a female produced over her lifetime. The temporal staggering of clutches strongly and negatively impacted survival of later clutches. The effect of spatial patterning of clutches on offspring fitness depended on the number of clutches in the fruit: at higher densities, clutches performed better when deposited into the same puncture than when distributed uniformly over fruit. The evidence taken together suggests that host reuse by the walnut fly, R. juglandis, reduces per capita offspring fitness. Consistent with this inference was a final set of observations on female host-marking behavior. In field-cage experiments, fruit that were marked by females for longer durations were less acceptable to other females. Moreover, the duration of time that a female marked a fruit was positively correlated with the size of her clutch. These results indicate that, while females commonly reuse fruit, they nevertheless signal the level of larval competition associated with a fruit and adjust allocation of eggs to fruit accordingly.

Although there is much information about insect associative learning, less is known about the underlying neural mechanisms. This is partly due to the lack of behavioral paradigms providing a suitable model for studying learning mechanisms at the level of individual neurons. This thesis describes the background to, and the demonstration of, two associative learning paradigms: visual associative learning and spatial learning. Both have been developed on the restrained cockroach so that later these methods can be employed in conjunction with electrophysiology. By projecting their antennae intermittently towards a position of potential food sources, cockroaches sample salient information. Here, this antennal behavior, called an "antennal projection response (APR)," is used to demonstrate long-term memory where an APR is elicited by a conditioning stimulus (CS: green light) paired with a spatially coincident odor (unconditioned stimulus: US). The acquired APR to the green light cue persists for up to 72 hours. Spatial learning is also a vitally important behavior in most animals that must remember locations of food and landmarks and that must navigate. Spatial learning abilities were here tested by observing APRs towards a cue, where the cockroach learns the position of a visual cue (CS) associated with a food odor (US), relative to the position of another visual stimulus in the contralateral visual field (the contralateral visual reference stimulus: ConRS). Memory of positional information, tested by altering the relative positions of the CS and ConRS, was investigated. Cockroaches showed significant APRs to visual cues not only when a position of the visual cue and spatial reference cue were exactly matched during training trials, but also during tests when the relative angles between the visual cue and spatial reference cue were matched but rotated around the head's vertical axis. When these angles were not the same as the angle used for training, the CS was not recognized. These results suggest that cockroaches employ two different mechanisms to find a food source: retinotopic matching and recognition of angular relationships between a source and landmark. The application of these paradigms to studies that could investigate possible neural mechanisms of these behaviors is discussed.

In this dissertation, the evolutionary and ecological determinants of host range of nematode parasites (Tylenchida: Allantonematidae: Howardula, Parasitylenchus) of mushroom-breeding Drosophila (Diptera: Drosophilidae) are examined. These nematodes are horizontally transmitted, obligate parasites, often with severe effects on host fitness. Phylogenetic analysis of Drosophila and Howardula DNA sequences shows little congruence between host and parasite phylogenies, with frequent host colonizations and losses. Drosophila -parasitic Howardula are not monophyletic, with host switches occurring between Drosophila and distantly related mycophagous sphaerocerid flies. Molecular analysis reveals eight new Howardula species. The ability of five nematode species to infect and develop in 24 taxonomically diverse Drosophila species is assessed. All nematode potential host ranges but one are large, even for host specialists. Novel hosts that are distantly related from the native host are less likely to be infected, but among closely related hosts there is variation in susceptibility. Potential host ranges differ greatly between related parasite species. Most novel infections do not cause reductions in host fecundity, with the exception of P. nearcticus. Thus, Drosophila-nematode associations are dynamic, and appear to be driven by a combination of repeated opportunities for host colonization due to shared mushroom breeding sites, and large nematode potential host ranges. Recent colonization of novel host species may explain the striking differences in virulence observed in natural Drosophila-nematode associations. For example, Nearctic species of the Drosophila testacea group are more severely affected by infection than Palearctic species, including complete female sterility. Cross-infection experiments reveal that virulence is evolutionarily labile in testacea-Howardula associations, and that high levels of virulence manifested in some host-parasite combinations are due to a lack of host resistance. Finally, ecological determinants of host range are considered. First, competition between a generalist and a specialist parasite of D. recens is assessed by comparing nematode infection success and reproduction in single and double infections. Second, differences between the actual and potential host ranges of Howardula neocosmis are documented. This parasite appears restricted to D. acutilabella in nature, yet successfully parasitizes the closely related, microsympatric D. cardini. Neither differential virulence nor competitive interactions between hosts explain the host range differences.

Sequestration of the blue biliprotein, insecticyanin, into developing oocytes of the hawkmoth, Manduca sexta was investigated using diverse techniques. Oudin's immunodiffusion assays revealed that insecticyanin concentration in mature eggs (29.6 μM) is slightly higher than that in hemolymph (25.8 μM). The endocytotic uptake of insecticyanin was visualized at the light microscopic level using autoradiography. Uptake of ¹²⁵I-insecticyanin by isolated oocytes was ligand specific, saturable with increasing insecticyanin concentration, and sensitive to parameters such as size of oocyte, constituents of media and temperature. Analysis of in vitro uptake data yielded values of K(uptake) (insecticyanin concentration at half-maximal uptake rate) of 4.2 μM and V(max) (maximum rate of uptake) of 1 pmol follicle⁻¹ h⁻¹. Oocyte membrane proteins were efficiently solubilized using 40 mM detergent CHAPS. Labeled insecticyanin was shown to bind to crude follicle membranes and solubilized membrane proteins with high specificity and affinity. The K(d) (equilibrium dissociation constant) was estimated as 40 nM and 17 nM for crude membranes and solubilized membrane proteins, respectively. The B(m) (maximum binding) estimated from crude membrane and solubilized membrane protein was 1.6 and 11.4 pmol/mg proteins respectively. Competition studies showed that binding of labeled insecticyanin to its receptor was blocked by an excess of unlabeled insecticyanin but not by other major hemolymph proteins, lipophorin and vitellogenin of M. sexta. Additional binding experiments demonstrated that receptors for insecticyanin are only present in oocyte membranes, not in fat body, gut tissue or ovariole. The results from co-immunoprecipitation showed that the apparent molecular mass for insecticyanin receptor is approximately 185 kDa on reducing SDS-PAGE gel while chemical crosslinking of the insecticyanin-receptor complex revealed a product with a molecular mass near 1000 kDa. This result suggests that the insecticyanin receptor has a multimeric structure, or that four receptor molecules can bind to one insecticyanin tetramer.

The evolution of wing morphology in three clades of Drosophila was investigated using a method of mapping a complex of continuous characters developed for landmark configurations. In the melanogaster subgroup, a rate test for morphological characters was applied using the mutation-drift equilibrium (MDE) model under a range of evolutionary scenarios. The results indicate that wing morphology has evolved at a slower rate than genital morphology. The rate test under the MDE model suggested that genital morphology has evolved at a neutral rate while wing morghology has been under stabilizing selection. In the cactophilic species of the repleta group endemic to the Sonoran desert, wings have evolved in response to two factors: adaptation to the density of rots in the host cacti and adaptation to Sonoran desert conditions. Aerodynamic parameters of the wing were calculated based on a steady-state aerodynamic model. Flies using larger host cacti tend to have wings of greater aspect ratio which are better suited for long range dispersal. Flies adapted to Sonoran desert conditions tend to have wings with broader bases and narrower tips, suggesting greater efficiency at fast forward flight. The evolution of wing pigmentation patterns in the Hawaiian picture-winged Drosophila was examined in a phylogenetic context. Four specific hypotheses were tested: (1) has the overall degree of pigmentation evolved from more lightly to more heavily pigmented wings; (2) has the evolution of pigmentation patterns proceeded through a process of elaboration resulting in patterns of greater complexity; (3) are the fundamental symmetries in pigmentation pattern the same for all species in this group; and (4) are the patterns of symmetry related to what is known about wing development in Drosophila melanogaster? The pattern of evolutionary changes in the level of pigmentation was not consistent with a hypothesis of gradual increase. Based on a measure of complexity derived from Shannon's information content, there is no compelling evidence to support the hypothesis of evolutionary elaboration of pattern. There is evidence for one major evolutionary shift in the pattern of symmetry. A model linking fundamental symmetries in pigmentation pattern to wing development is presented.