Thesis (M.S.)--University of California, Berkeley, 1913. / Includes bibliographical references (leaves [12-13]).

Four separate but complimentary studies investigated the role of grain sorghum as a predator source for Southern Rolling Plains cotton in 2001 and 2002. Objectives were to: (1) determine the timing and magnitude of predator movement between crops, (2) test putative causes of movement by manipulating prey levels at different stages of crop phenology, (3) explore the feeding and reproductive behavior of a common predator colonizing cotton, and (4) examine the effects of grain sorghum and uncultivated areas on cotton predator abundance at an area-wide scale. Rubidium mark-recapture experiments indicated grain sorghum fields produced a net predator gain for adjacent cotton. Analysis suggested two coccinellids, Hippodamia convergens Guérin-Méneville and Scymnus loewii Mulsant, were responsible for the overall pattern of predator movement. Predator movement into cotton did not appear to be concentrated at specific stages of sorghum phenology. Manipulations of aphid levels in field cages were used to determine if prey abundance or phenology influenced the movement of H. convergens into cotton. In both years, more lady beetle adults were collected on cotton during the latest stages of sorghum phenology. In the second year, relatively low aphid densities (15 per plant) appeared to influence the movement of beetles onto caged cotton. Carbon isotope ratios of H. convergens were used to assess adult feeding behavior after colonizing cotton and to determine if prey consumed in sorghum contributed to egg production in cotton. Though aphids were absent 2001, H. convergens adults stayed in cotton, did not produce eggs and apparently consumed few prey. Cotton aphids were present in 2002 and H. convergens isotope ratios changed from prey consumed in cotton. The isotope ratios of egg masses collected in 2002 indicated prey consumed in grain sorghum contributed very little to egg production in cotton. An area-wide pattern analysis suggested the abundance of grain sorghum and uncultivated areas both positively influenced cotton predator levels. While these landscape effects were less important overall than prey levels and cotton planting dates, in some sampling periods landscape composition appeared to be the most important factor in determining cotton predator levels.

Four separate but complimentary studies investigated the role of grain sorghum as a predator source for Southern Rolling Plains cotton in 2001 and 2002. Objectives were to: (1) determine the timing and magnitude of predator movement between crops, (2) test putative causes of movement by manipulating prey levels at different stages of crop phenology, (3) explore the feeding and reproductive behavior of a common predator colonizing cotton, and (4) examine the effects of grain sorghum and uncultivated areas on cotton predator abundance at an area-wide scale. Rubidium mark-recapture experiments indicated grain sorghum fields produced a net predator gain for adjacent cotton. Analysis suggested two coccinellids, Hippodamia convergens Guérin-Méneville and Scymnus loewii Mulsant, were responsible for the overall pattern of predator movement. Predator movement into cotton did not appear to be concentrated at specific stages of sorghum phenology. Manipulations of aphid levels in field cages were used to determine if prey abundance or phenology influenced the movement of H. convergens into cotton. In both years, more lady beetle adults were collected on cotton during the latest stages of sorghum phenology. In the second year, relatively low aphid densities (15 per plant) appeared to influence the movement of beetles onto caged cotton. Carbon isotope ratios of H. convergens were used to assess adult feeding behavior after colonizing cotton and to determine if prey consumed in sorghum contributed to egg production in cotton. Though aphids were absent 2001, H. convergens adults stayed in cotton, did not produce eggs and apparently consumed few prey. Cotton aphids were present in 2002 and H. convergens isotope ratios changed from prey consumed in cotton. The isotope ratios of egg masses collected in 2002 indicated prey consumed in grain sorghum contributed very little to egg production in cotton. An area-wide pattern analysis suggested the abundance of grain sorghum and uncultivated areas both positively influenced cotton predator levels. While these landscape effects were less important overall than prey levels and cotton planting dates, in some sampling periods landscape composition appeared to be the most important factor in determining cotton predator levels.

Aphidophagous lady beetles rely on multiple sources of food in their environment. Alfalfa fields provide both aphids and many alternate foods, such as other arthropod prey, pollen, and fungi. Alfalfa fields (Medicago sativa L.) in Utah have low aphid densities, which may require lady beetles to consume alternative sources of food. Many methods can be used to determine these diets; frass analysis is used here to compare the diets of the introduced species Coccinella septempunctata L. with two native species, C. transversoguttata richardsoni Brown and Hippodamia convergens Guérin-Méneville, that occur in the Utah alfalfa habitat. In initial laboratory experiments to examine the feasibility of frass analysis, 48 hours at 20oC was sufficient time for adult lady beetles to pass prey cuticle through their guts. When consumed by these adults, pea aphids (Acyrthosiphon pisum [Harris]), alfalfa weevil larvae (Hypera postica [Gyllenhall]), and C. septempunctata larvae produced distinctive fragments in the frass. Such fragments could also be distinguished in frass collected in a field experiment in which aphid densities in plots of alfalfa were manipulated. Furthermore, additional consumed foods could be distinguished in the field experiment, including pollen, fungi, and other types of arthropods. Frass analysis demonstrated higher use of aphid prey by C. septempunctata adults collected from high versus low aphid density plots during the field experiment. Use of other types of prey, such as alfalfa weevil larvae, other arthropods, pollen and fungi, was similar between plots with high and low aphid densities. A field census was performed over two years to track the diets of the three species of lady beetles during the first crop of alfalfa, when two sources of prey in particular were present, aphids and alfalfa weevil larvae. Comparisons of diets revealed that the three species utilized different types of prey to similar degree during both years. In general, however, higher percentages of C. septempunctata adults were found to have consumed aphids and weevils during both years. Also, C. septempunctata was found to produce more frass and consume larger quantities of prey than either native species during the second year.

Aggregative feeding is widespread in Lepidopteran larvae suggesting that this behavior serves on adaptive function. Many studies of the potential benefits of aggregative feeding in Lepidopteran larvae have been conducted. However, no studies have directly examined the benefits of cryptic larvae being both chemically defended and gregarious. Group feeding occurs disproportionately more in chemically defended larvae than in larvae that have no chemical defense. Most of these larvae are cryptic when they are most highly aggregated and most vulnerable to predation. In this study, the benefits of group feeding in terms of decreased predation were explored in first instar larvae of pipevine swallowtail larvae, Battus philenor, a species that exhibits chemical sequestration. Contrary to our expectation, we found that groups of larvae fed a diet with high levels of the toxin aristolochic acid, which they sequester naturally and use as a defense against natural enemies, had significantly lower survivorship due to predation in both the field and in the laboratory experiments compared to groups of larvae fed a diet with low aristolochic acid content. We also found that aristolochic acid does not deter the generalist predator Hippodamia convergens, the ladybird beetle, suggesting that this compound is not a universal predator deterrent as previously assumed. Thus, instead of finding a benefit to group feeding and chemical defense in cryptic larvae, we have found a negative impact of group feeding in this population of B. philenor. Based on this evidence, we speculate that other benefits of group feeding might be outweighing the negative consequences of increased predation during the first instar. Future research on chemical defense, aposematism, and aggregative feeding should take into consideration that chemical defenses might not be universally effective against all natural enemies.

No description available.

Master of Science / Department of Entomology / Brian P. McCornack / Winter canola production in the south-central US is commonly threatened by a complex of aphid species that can cause up to 70% in yield loss. Aphid species vary in their life-history traits, performance (sequestration/excretion of secondary compounds; glucosinolates), vertical distribution within the plant, and temporal dynamics across the growing season. Colonizing behavior of these aphids may be affected by intrinsic characteristics of the host plant (bottom-up effects), such as nutritional value, secondary compounds, or plant architecture. Understanding bottom-up effects may enable the evaluation of plant-level interactions that are influencing predator-prey dynamics. The goal of my research project is to understand aphid population dynamics in different canola plant structures, assess whether aphid quality (sequestration/ excretion of glucosinolates) is influenced by feeding location on the canola plant, and if so, assess the impact on the existing predator communities, specifically the development and fitness of immature and adult Hippodamia convergens. A combination of filed and greenhouse experiments provided novel contributions that will help shape our understanding of key factors regulating aphid population growth in canola fields, which will lead to more judicious use of insecticides and better sampling strategies.

Doctor of Philosophy / Department of Entomology / J.P. Michaud / James R. Nechols / The manner in which organisms allocate reproductive resources for reproduction is a central question with respect to life history theory. The main objectives of this research were to i) examine lifetime patterns of reproductive allocation in the lady beetles Coleomegilla maculata (DeGeer) and Hippodamia convergens (Guérin-Menéville) (Coleoptera: Coccinellidae) while manipulating environmental conditions that affect female body size (i.e., larval food supply), ii) to study the interaction between factors underlying female body size and the resources available during reproduction, and iii) to explore the maternal effects of female size and age on the development and survival of progeny. When different size classes of females were produced and adult females were maintained with unlimited food, there were no differences in egg size across female size in C. maculata, but egg size increased over time in all females. In H. convergens, only larger females increased egg size over time, and they laid larger eggs, on average, than did small females. Maternal body size was positively correlated with the number of eggs laid per day in both species. When three size classes of females were subjected to a fluctuating food supply as adults, female size was again positively correlated with egg and daily fecundity. Whereas both species varied daily fecundity in response to adult food supply, egg size was unaffected and demonstrated a fixed pattern of change with female age and species-specific effects of maternal body size. To observe maternal effects in H. convergens, three female size classes were again produced and progeny were reared from three different periods of each female‟s reproductive life. Offspring from later oviposition days and larger females developed faster and achieved larger adult size than those reared from earlier oviposition days. Egg size showed inconsistent correlations with developmental parameters and adult progeny size, so other, more cryptic, maternal signals were inferred to signal phenotype development in progeny. A fixed program of producing faster-developing offspring that mature to larger sizes late in the oviposition cycle is adaptive for exploiting ephemeral aphid blooms that exhibit predictable dynamics of declining prey abundance and increasing competition. In the case of H. convergens, resource limitation during development constrained not only body size, fecundity and egg size, but also maternal ability to manipulate progeny phenotypes.