Geocoris bullatus (Say 1831), (Henriptera: Lygaeidae) has been collected and studied across North America but the present work is the first detailed study of western North American G. discopterus Stål 1874. In fact, it has been claimed that G. discopterus is solely a species of the east. As the two species are taxonomically difficult to separate, when they were apparently discovered together at several localities in the southwestern Yukon, a detailed investigation of their systematics and distribution seemed necessary. Species status of Yukon G. bullatus and G. discopterus was established morphologically using standard taxonomic characters. Biological species status was confirmed through breeding experiments. The life cycles of Yukon G. bullatus and G. discopterus were studied and significant differences were discovered in the generation time and phenology. G. discopterus is univoltine and usually overwinters in the adult stage, while G. bullatus is bivoltine and overwinters in the egg stage. Fat body dissections revealed adult G. discopterus fat body size increased toward the end of summer. No such trend was recognized in adult G. bullatus. Total fatty acid levels were assayed for each species, and adult G. discopterus were found to contain higher quantities than G. bullatus, perhaps correlating with the overwintering strategy in G. discopterus An investigation of the habitats occupied by each species was performed through an in depth vegetation analysis. G. discopterus was found to prefer xeric sites situated on south-facing slopes and outwash plains while G. bullatus occupied disturbed mesic roadsides and wastelands. Habitat preference differences coupled with phenological differences may account for the apparent sympatry of these two Geocoris species at some Yukon localities. Comparison of the xeric habitat of G. discopterus to known glacial relict sites in the interiors of Alaska, Yukon and Siberia reveal striking similarities. Late Pleistocene pollen cores also compare favorably with these G. discopterus habitats. In view of this and the disjunct North American distribution of G. discopterus, this species is hypothesized to be a relict species from the late Pleistocene ice age. / Science, Faculty of / Zoology, Department of / Graduate

Specific aspects of the selective sequestration, excretion and tolerance of cardenolides in the large milkweed bug, Oncopeltus fasciatus have been studied using spectrophotometry assays, thin-layer chromatography, tracer studies, in vivo tolerance assays, and enzyme inhibition techniques. The cardenolide content of the dorsolateral space, gut, wings and fat body of Oncopeltus fasciatus was examined. The results indicate that the majority of cardenolides sequestered in the insect are concentrated in the dorsolateral space, which confirms the basic pattern of quantitative distribution of cardenolides in O. fasciatus determined in earlier work. Large amounts of cardenolides were not found in the gut, wings and fat body. The female fat body contained 4-5% of the total cardenolide content of the insect. The cardenolide content of male fat body, and gut and wings of both sexes was below the detection limit of the cardenolide assay. Thin-layer chromatography was used to determine the cardenolide array of various tissues and secretions of O. fasciatus reared on seeds of a single species of milkweed (A. speciosa) and adult extracts and dorsolateral space fluid of O. fasciatus reared on seeds of two species of milkweed with different cardenolide arrays (A. speciosa and A. syriaca). The results indicate that cardenolides are not sequestered in the insect simply on the basis of polarity and that metabolism and differential excretion of cardenolides are involved in the sequestration of cardenolides in O. fasciatus.. The similarities in the cardenolide profiles of O. fasciatus reared on different food sources, and tissues of O. fasciatus reared on a single food source indicates that there is regulation of the cardenolide array in O. fasciatus. An in vitro preparation of Malpighian tubules was used to investigate the excretion of the polar cardenolide, ouabain, in O. fasciatus. Both segments of the tubules were found to metabolize ouabain. The distal Segment (Segment II) secreted primary urine and ouabain. Secretion of ouabain by Segment II was not observed to occur against a concentration gradient and increased with increasing fluid secretion. The proximal segment (Segment I) reabsorbed fluid and ouabain but not metabolites of ouabain. Ouabain was reabsorbed against a strong concentration gradient (23-fold), was independent of fluid reabsorption, and increased with increasing fluid secretion by Segment II. In rapidly secreting Malpighian tubules (a situation of high cardenolide secretion by Segment II), the presence of Segment I reduced the excretion of ouabain by 84 - 93%, mainly by reducing ouabain concentration. It appears excretory loss of cardenolides can be reduced in O. fasciatus and thus may be a factor in the sequestration of cardenolides in this insect. O. fasciatus tolerated 1954x and 7288x, respectively, the LD₅₀ ouabain dose of Schistocerca gregaria and Periplaneta americana when ouabain was injected into the hemocoel of these insects. The maximum ouabain dose that could be injected into 0. fasciatus (200 nmoles) resulted in no mortality; this dose is higher than the lethal ouabain doses recorded for vertebrates and invertebrates. The ouabain concentration resulting in 50% inhibition (I₅₀) of Na,K-ATPase activity was determined in lyophilates of nervous tissue of 0. fasciatus and brain and recta of S. gregaria and were 2.0 x 10⁻⁴, 2.0 x 10⁻⁶, and 1.0 x 10⁻⁶ M, respectively. The I₅₀ value for ouabain inhibition of Na,K-ATPase activity in the nervous tissue of O. fasciatus is higher than the I₅₀ values for nervous tissue in most other insects as well as many other invertebrate and vertebrate tissues. Thus, the presence of ouabain resistant Na,K-ATPases appears to be a factor in the tolerance and sequestration of plant cardenolides in O. fasciatus. / Science, Faculty of / Zoology, Department of / Graduate

Field studies of population of Geocoris and Nabis indicated that the density of adult Nabis was higher than Geocoris before April, but the reverse was true after April. In general, the abundance of adults and nymphs of each species was caused by alfalfa harvesting, dispersal of adults, discrepancies of sweep-net sampling, differences in mortality of eggs and the differences in the diapause termination of adults. The field cuttings of alfalfa reduced populations of both species, but adults were reduced more than the nymphs. In laboratory studies adults and nymphs of each species fed on each other on alfalfa in small cages, but in larger cages when only adults were caged, interspecific predation of adults did not occur. This suggests that, in the field, interspecific predation of nymphs can be more prevalent than adults of each species since nymphs which are more sedentary than adults are less affected by alfalfa cuttings. A number of predatory insects other than Nabis that were common in the alfalfa, such as Chrysopa carnea Stephens, Orius tristicolor (White), Hippodamia convergens Guerin, and Sinea confusa Caudell, were also found to prey upon Geocoris in the laboratory. Hyalomya aldrichii Townsend was the only parasite reared from Geocoris adults and nymphs from the field. The parasite did not numerically respond to the density of Geocoris and had minor impact on the population of the predator. The host preference of this parasite among the Geocoris spp. and between Geocoris and Nabis was not determined since rearing the parasite in the laboratory failed. Telenomus sp. parasitized groups of Geocoris eggs exposed in alfalfa fields. In the laboratory, it parasitized both G. pallens and G. punctipes eggs. Rearing the parasite at 30(DEGREES)C resulted in poorer emergence of adults than at 20(DEGREES)C and 25(DEGREES)C. Predaceous insects that synchronize with populations of Geocoris, larger in size then Geocoris, especially Nabis and Sinea spp. may be more important than parasites in regulating population of Geocoris in the field.

Sexual selection arises via competition for access to mates, and is thus intimately tied to the social environment. For example, individual mating success may depend strongly on how many rivals or mating partners are available. Studies of mate choice and sexual selection may vary the number of mates a subject is presented with during mating experiments, yet it is not clear how this influences the strength and shape of sexual selection acting on traits in either sex. In this thesis I investigate the effect of social environment on sexual selection acting in two closely-related species of lygaeid seed bug: Lygaeus equestris and Lygaeus simulans. Males in both species possess an extremely elongate intromittent organ, which is over two-thirds average male body length. I show that the strength of pre-copulatory selection acting on male processus length in Lygaeus equestris and genital clasper shape in Lygaeus simulans is significantly influenced by the social context. However, selection on male and female body size in Lygaeus equestris is not. Additionally, I use a meta-analysis of 38 published studies to show that mating preferences are significantly stronger when more than one mate option is available, compared to when only a single option is available. I also investigate the functional morphology of male genital traits in Lygaeus simulans, and use formal selection analysis to quantify the strength of selection acting on these traits before, during and after mating. Finally, I use experimental manipulations in Lygaeus simulans to confirm that male processus length directly influences sperm transfer, and that intact genital claspers are required for successful intromission. Overall, my results illustrate that sexual selection in the wild may vary both spatially and temporally depending on the social environment. It is thus especially important that experiments are performed under ecologically relevant conditions.