Browsing by Subject "biological control"
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Item An evaluation of two strains of Cyrtobagous salviniae Calder and Sands as natural enemies of the aquatic weeds salvinia molesta Mitchell and Salvinia minima Baker(Texas A&M University, 2006-04-12) Dye, Jeremiah M.The floating aquatic weeds common salvinia (Salvinia minima Baker) and giant salvinia (Salvinia molesta Mitchell) degrade aquatic systems through fast, mat forming growth. The Salvinia specialist weevil Cyrtobagous salviniae Calder and Sands has been used to reduce the severity of giant salvinia infestations and associated with reduced severity of common salvinia infestations. Genetically, morphologically and biologically distinct strains of C. salviniae exist, but their relative potential for success as biological control agents of Salvinia species has not been evaluated. This thesis (1) describes a recirculating water system designed for conducting such studies and (2) reports the results of C. salviniae strain comparisons. A recirculating water system with a high degree of replication and minimal variation in water flow, temperature and light intensity was used for laboratory experiments using sixty-day temperature profiles averaging 31.4, 26.5 and 8.0?C derived from surface water temperatures measured at lakes in expected range of Salvinia species in the North America. Larval and adult population numbers of two C. salviniae strains (Australia and Florida) were determined for each temperature profile along with feeding induced plant necrosis on both Salvinia species. Australia C. salviniae had lower survivorship rates to adulthood on common salvinia than did Florida C. salviniae at the 31.4 and 26.5?C temperature profiles. Neither strain reproduced, and no significant between-strain differences in plant necrosis were detected at the 8.0?C temperature profile. At 31.4?C there were no significant differences in adult counts, larval counts or plant damage between the two strains on giant salvinia. At 26.5?C, however, significantly fewer larvae were collected from initially released adults and significantly less plant necrosis was associated with weevil feeding by Florida strain compared to Australia strain weevils. These results may have arisen from comparing Australia weevils from a growing colony to Florida weevils from a declining colony. Overall, the results indicate that only Florida C. salviniae should be released against common salvinia. Florida C. salviniae may be equally suitable to Australia C. salviniae for releases against giant salvinia, but further study is needed to fully assess the potential for using Florida C. salviniae against giant salvinia.Item Courtship acoustics and mating in Cotesia, a genus of parasitoid wasps(2009-05-15) Joyce, Andrea LeeCotesia are parasitoid wasps (Hymenoptera: Braconidae) that are used for biological control of pest moths (Lepidoptera: Noctuidae, Pyralidae) that damage agricultural crops. This dissertation investigated courtship acoustics and mating, and their relevance to biological control, in members of the Cotesia flavipes species complex, and a noncomplex member, Cotesia marginiventris. The first study investigated whether courtship acoustics were species specific for two members of the Cotesia flavipes complex, C. flavipes and C. sesamiae, and for C. marginiventris. During courtship, male Cotesia fan their wings and produce low amplitude sounds and substrate vibrations. The airborne and substrate components of courtship were similar within a species. However, the courtship acoustics of each species was distinct. The duration and frequency of several courtship acoustic components distinguished each species, while some components did not differ among species. The second study investigated mating success and transmission of courtship vibrations on natural and artificial rearing substrates for Cotesia marginiventris. Mating success was measured on plastic, glass, corn and bean leaves, and chiffon fabric. Mating success was lowest on plastic and glass, intermediate on corn and bean leaves, and highest on chiffon. Substrate influenced transmission of courtship vibrations. Durations of courtship vibrations were longer on corn, bean and chiffon than on plastic. Frequency modulation occurred on corn, bean and chiffon, and amplitude was greatest on chiffon. The mating success of normal and dealated males was higher on chiffon than on glass, suggesting that courtship communication relied in part on substrate vibrations. The third study examined female and male mate choice in a solitary and a gregarious species, C. marginiventris and C. flavipes, respectively. Females of the solitary species, C. marginiventris, mated more frequently with large than small males, and this did not appear to be the result of male competition. Male choice for female size was not apparent in C. marginiventris. Females of the gregarious parasitoid, C. flavipes, mated with large or small males with similar frequencies, and male-male competition was not observed. In the male choice experiment, C. flavipes males attempted copulation and mated more with smaller females, and smaller females accepted males more than large females.Item Dynamics of water use and responses to herbivory in the invasive reed, Arundo donax (L.)(2010-07-14) Watts, David A.The first objective of this study was to investigate the role of an invasive grass species, Arundo donax (L.), on the hydrologic cycle. At a site on the Rio Grande in South Texas, we measured the gas exchange of carbon dioxide and water vapor at the leaf scale and structural characteristics, such as leaf area and shoot density, at the stand scale. In order to assess the effect of water availability, this study was conducted along transects perpendicular to the edge of the river along a potential moisture gradient. The second objective was to quantify the effect of two herbivores, an armored scale, Rhizaspidiotus donacis (Leonardi), and a stem-galling wasp, Tetramesa romana (Walker),on the photosynthetic and transpiration rates of A. donax. Leaf gas exchange measurements were made to determine the direction and magnitude of the effect on physiological processes and by what mechanisms any effects arose. Stands of A. donax used approximately 9.1 ? 1.1 mm of water per day. This rate of water use was at the high end of the spectrum for plants. The major controls on stand scale transpiration were evaporative demand, leaf area index, and water availability. During two summer seasons, stand scale transpiration varied greatly, following the pattern of variability in precipitation, suggesting that recent rainfall constituted a significant proportion of the water taken up by this species. Herbivory by a stem-galling wasp and a sap-feeding scale, both separately and together, reduced the rates of leaf scale physiological processes in A. donax. The efficacy of the wasp was density dependent, and this herbivore reduced the carboxylation rate of Rubisco. The effect of the scale took approximately five months to manifest, which coincided with generation time. Scale reduced photosynthesis by decreasing the maximum rate of electron transport. When the two insects were both present, the effect of their herbivory seemed to be additive. These results will assist the responsible management agencies in evaluating the propriety of using one or both of the insect herbivores as biological control agents.Item Host habitat location mediated by olfactory stimuli in anaphes iole (hymenoptera: mymaridae), an egg parasitoid of lygus hesperus (hemiptera: miridae)(Texas A&M University, 2005-02-17) Manrique, VeronicaLygus hesperus is an important pest on different crops including cotton and alfalfa in the western U.S. Anaphes iole is a common parasitoid of Lygus spp. eggs in the U.S. and has potential as a biological control agent against L. hesperus in different crops. Its foraging behavior has been studied to a limited extent, but it is unknown whether A. iole females rely on plant volatiles to locate host habitats. L. hesperus feeding and oviposition are known to induce emission of plant volatiles in cotton and maize, but no studies have addressed the role of plant volatiles in the host searching behavior of A. iole. The objectives of this study were to evaluate the attraction of A. iole females toward volatiles derived from L. hesperus habitats and flight response of A. iole females toward cotton plants harboring L. hesperus eggs or treated with methyl jasmonate. Results from olfactometry bioassays showed that female wasps were attracted to odors emanating from different plant-L. hesperus complexes and from adult L. hesperus, while plants damaged by non-hosts or mechanically-damaged were not attractive. These findings suggested that A. iole females use specific plant volatiles released following L. hesperus feeding and oviposition to locate host habitats. In addition, in flight chamber tests A. iole females discriminated between cotton plants with moderate (41 eggs) and high (98 eggs) levels of L. hesperus infestations relative to uninfested plants, but not between plants with low (7 eggs) infestations compared to uninfested plants. In larger scale experiments conducted in the greenhouse, female wasps responded to L. hesperus-infested plants but not to methyl jasmonate-treated plants under similar conditions. Overall, results from this study revealed that A. iole females employ volatile signals to locate its host?s habitat and that they are attracted to plants damaged by L. hesperus feeding and oviposition. However, further research should seek to identify the chemical elicitors involved in the release of plant volatiles attractive to A. iole females.Item Impact of interspecific interactions among parasitoids on inoculative biological control of leafminers attacking chrysanthemum(Texas A&M University, 2007-09-17) Bader, Amy ElaineIndigenous natural enemies occur within field grown crops at varying densities dependent upon a variety of other biotic and abiotic parameters. This natural control often does not provide adequate suppression, which results in the application of other remedial pest management solutions including augmentative biological control. When releasing mass-reared natural enemies into a backdrop of indigenous natural enemy populations, competitive interactions are likely to occur. To assess the influence of these interspecific interactions on the outcome of such biological control practices, studies were conducted both in a laboratory and in a simulated, field grown, cut chrysanthemum (Asteraceae: Dendranthema grandiflorum) production system. Competitive interactions of two commercially available parasitoids were studied both in terms of parasitoid-host population dynamics and the impact of interspecific interactions on crop quality at harvest in this type of system. The parasitoids Diglyphus isaea and Dacnusa sibirica attacking the leafminer Liriomyza langei were used as the model insect system. Both parasitoids are cosmopolitan and are known to occur in many ornamental production areas. Conclusions drawn from laboratory experiments were that D. sibirica produces more offspring that D. isaea over approximately the same number of days. Treatment comparisons in the field included single species releases with complimentary releases of both species either simultaneously or with two-week time lags, as well as a no release control to measure the background effects of natural mortality. Conclusions drawn from results of population-level studies replicated within and among years were that levels of interspecific competition among parasitoid species were undetectable at leafminer densities typical of field-grown ornamental crops; thus, the efficacy of one species released into a backdrop of potentially competing parasitoids did not negatively affect the outcome of the augmentative biological control. The two species were able to coexist inside field cages for the duration of the crop. Most of the release treatments suppressed host densities lower than the control cages where no parasitoids were released, and there were no treatment effects on host suppression. Even though parasitoid release combination did affect the amount of damage visible at harvest, there was no influence on the number of flowers produced (yield).Item Impact of the red imported fire ant upon cotton arthropods(Texas A&M University, 2004-09-30) Diaz Galarraga, Rodrigo RogelioInclusion/exclusion field experiments demonstrated that the red imported fire ant, Solenopsis invicta Buren, did not affect the abundance of 49 groups of insects and spiders collected in pitfall traps. However, arthropod diversity was significantly greater (H' = 2.829) in exclusion plots relative to inclusion plots (H' = 2.763). Moreover, this study demonstrated that S. invicta can have an important impact upon cotton arthropod communities, including key predator species. Densities of ground beetles (Carabidae), spiders, lacewings (Chrysoperla spp.), and minute pirate bugs (Orius spp.) were significantly lower in the presence of S. invicta. However, populations of aphidophagous insects such as Hippodamia spp. and Scymnus spp. increased with cotton aphid (Aphis gossypii Glover) density early in the season. Abundance of cotton aphids was ca. 5x greater in inclusion plots, likely due to protection and tending by S. invicta. This increase was observed early in the season, though aphid populations did not reach economic levels. Predation of sentinel bollworm [Helicoverpa zea (Boddie)] and beet armyworm (Spodoptera exigua Hubner) eggs increased 20-30%, when S. invicta was present. Most predation of sentinel beet armyworm egg masses, measured via direct nocturnal observations, was due to S. invicta (68%) and cotton fleahopper [Pseudatomoscelis seriatus (Reuter)] (21%) in plots with S. invicta, and by the mite Abrolophus sp. (52%), spiders (13%) and minute pirate bug (13%) in plots without S. invicta. The frequencies of minute pirate bug, cotton fleahopper, S. invicta and native ants in beat bucket samples did not accurately reflect the frequency with which they were observed feeding on sentinel noctuid eggs. Overall, the results of these studies demonstrated that S. invicta was associated with declines in the abundances of minute pirate bug, spiders, and lacewing and with an increment in cotton aphid populations, though they did not reach the economic threshold. Moreover, S. invicta significantly increased predation of bollworm and beet armyworm eggs. All together, the results suggested that S. invicta has a net positive impact on cotton pest management.Item Invasive interactions of Monomorium minimum (Hymenoptera: Formicidae) and Solenopsis invicta (Hymenoptera: Formicidae) infected with Thelohania solenopsae (Microsporida: Thelohaniidae)(Texas A&M University, 2006-08-16) Keck, Molly ElizabethThelohania solenopsae Knell, Alan, and Hazard is an internal microsporidian that parasitizes the red imported fire ant, Solenopsis invicta Buren. This experiment studied the invasive interactions between the native United States ant, Monomorium minimum (Buckley), and S. invicta colonies infected with T. solenopsae and S. invicta colonies free of parasites. This study utilized S. invicta colonies of 100, 300, 600, 800, and 1000 workers to determine the ability of 1000 M. minimum workers to invade each S. invicta colony size. There was a significant difference in the time for M. minimum to invade S. invicta when comparing S. invicta colonies of 1000 workers infected with T. solenopsae to S. invicta colonies that were uninfected. It was also determined that there was a significant difference in the time for M. minimum to invade smaller uninfected S. invicta colonies as opposed to larger uninfected S. invicta colonies. There was no significant difference in the ability of M. minimum to invade smaller S. invicta colonies infected with T. solenopsae as opposed to larger infected S. invicta colonies. It was therefore concluded that S. invicta colonies infected with T. solenopsae were not able to defend their colony or prevent competing ants from invading as well as uninfected S. invicta colonies. This study also demonstrated that M. minimum is a significantly more invasive species when compared to S. invicta, invading S. invicta territories in every situation and doing so in a significantly shorter period of time than S. invicta colonies invaded M. minimum colonies.Item The role of grain sorghum in conservation of predatory arthropods of Texas cotton(Texas A&M University, 2004-09-30) Prasifka, Jarrad ReedFour 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 Gu?rin-M?neville 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.Item Tri-trophic Analyses of Rice, the Sugarcane Borer, and Putative Biological Control Agents(2010-01-14) Lv, JialeA three-year field experiment was conducted to evaluate the tolerance and compensatory response of rice (Oryza sativa L.) to injury caused by the sugarcane borer, Diatraea saccharalis (F.). Two mechanisms of within-plant tolerance/compensation were observed. Stem injured plants produced ca. 0.69 more tillers than uninjured plants, while tillers with leaf and leaf sheath injury produced larger panicles, up to 39.5% and 21.0% heavier than uninjured tillers, when injury occurred at 3rd tiller stage and at panicle differentiation, respectively. A 2-year field cage experiment was conducted to determine the biological control potential of Cotesia flavipes (Cameron) against the sugarcane borer on rice. The effective search rate was 49 cm2 ground area (2.2 tillers) parasitoid-1 day-1. A cohortbased age-structured model was developed to simulate the population dynamics and economic value of the sugarcane borer and C. flavipes in rice, as affected by overwintering larval density, timing and rate of parasitoid aerial release, and year-to-year climate (temperature and rainfall). The results suggest C. flavipes was most effective when released during the 1st sugarcane borer generation. The maximum simulated economic benefit ($112.05 ha-1) was ca. 7.8% of that provided by insecticide-based control. The inability of C. flavipes to provide economic control in temperate-subtropical areas is due to its high rearing cost, a low effective search rate, a low maximum rate of parasitism per female, and both spatial and temporal asynchrony of parasitoid emergence with the larval hosts. The biocontrol capability of Trichogramma galloi Zucchi was also simulated. The maximum economic benefit provided by T. galloi was $1128.75 ha-1, ca. 79.0% of that provided by insecticide-based control. Theoretical analyses were conducted to estimate the effectiveness of augmentative releases, using data from previous studies of parasitism of lepidopteran pests by hymenopteran parasitoids with host and parasitoid density as factors. The maximum daily parasitism per female was highest for parasitoids that attack exposed larvae, followed by parasitoids that attack eggs, semi-exposed larvae, and concealed larvae. Simulation analyses were conducted to estimate the population dynamics and economic value of D. saccharalis, herein used as a model host, and each of 5 parasitoid categories (solitary parasitoids that attack eggs, exposed larvae, and semi-exposed larvae, gregarious parasitoids that attack eggs and concealed larvae) in rice, as affected by overwintering larval density, timing of parasitoid release, and year-to-year climate. Among the 13,500 simulations that were conducted, 480 (3.6%) provided a greater economic value than insecticide-based control. All 480 simulations were obtained using solitary parasitoids that attack exposed or semi-exposed larvae. Solitary egg parasitoids provided an average of 42.2% of the economic value provided by insecticide-based control when released 30 days after planting. Gregarious parasitoids that attack eggs or concealed larvae provided almost no positive economic benefit. For parasitoid species that do not overwinter successfully in areas where they are released or that exhibit temporal or spatial asynchrony with their host early in the spring, our results suggest augmentative biological control is only effective for solitary parasitoids that attack either exposed or semi-exposed larvae, with current rearing, shipping and release costs.