269 research outputs found
Clifford Donahue and Shirley Weldon
No full textPhotograph - Clifford Donahue sitting and Shirley Weldon, Athabasca, Albert
Trapping to monitor tephritid movement: Results, best practice, and assessment of alternatives
No full textMovement of tephritid flies underpins their survival, reproduction, and ability to establish in new areas and is thus of importance when designing effective management strategies. Much of the knowledge currently available on tephritid movement throughout landscapes comes from the use of direct or indirect methods that rely on the trapping of individuals. Here, we review published experimental designs and methods from mark-release-recapture (MRR) studies, as well as other methods, that have been used to estimate movement of the four major tephritid pest genera (Bactrocera, Ceratitis, Anastrepha, and Rhagoletis). In doing so, we aim to illustrate the theoretical and practical considerations needed to study tephritid movement. MRR studies make use of traps to directly estimate the distance that tephritid species can move within a generation and to evaluate the ecological and physiological factors that influence dispersal patterns. MRR studies, however, require careful planning to ensure that the results obtained are not biased by the methods employed, including marking methods, trap properties, trap spacing, and spatial extent of the trapping array. Despite these obstacles, MRR remains a powerful tool for determining tephritid movement, with data particularly required for understudied species that affect developing countries. To ensure that future MRR studies are successful, we suggest that site selection be carefully considered and sufficient resources be allocated to achieve optimal spacing and placement of traps in line with the stated aims of each study. An alternative to MRR is to make use of indirect methods for determining movement, or more correctly, gene flow, which have become widely available with the development of molecular tools. Key to these methods is the trapping and sequencing of a suitable number of individuals to represent the genetic diversity of the sampled population and investigate population structuring using nuclear genomic markers or non-recombinant mitochondrial DNA markers. Microsatellites are currently the preferred marker for detecting recent population displacement and provide genetic information that may be used in assignment tests for the direct determination of contemporary movement. Neither MRR nor molecular methods, however, are able to monitor fine-scale movements of individual flies. Recent developments in the miniaturization of electronics offer the tantalising possibility to track individual movements of insects using harmonic radar. Computer vision and radio frequency identification tags may also permit the tracking of fine-scale movements by tephritid flies by automated resampling, although these methods come with the same problems as traditional traps used in MRR studies. Although all methods described in this chapter have limitations, a better understanding of tephritid movement far outweighs the drawbacks of the individual methods because of the need for this information to manage tephritid populations
The effect of black consciousness and black identity on the self-concept of black elementary school children, 1980
No full textThe purpose of this exploratory investigation was to analyze the effects of the dimensions of Black consciousness and identity on the self-concepts of Black sixth elementary school children and their all Black educators in traditional schools compared to Black sixth grade elementary school children and their Black and white educators in non-traditional schools. In addition, the study attempted to determine if there were any differences in the way which the two groups perceived themselves from a perspective. Methods and Procedures This study uses the descriptive survey method and the anthropological field method. The study is ejc post facto in that it is aimed at discovering the relations and interactions among sociological, psychological and educational variables in real social structures" (Kerlinger, 1973, p. 37 9). Observations and interviews were employed using specific questions taken from the two instruments designed for this study by the researcher. The descriptive questionnaires: Educators' Self-Identity Questionnaire (ESIQ) and Self-Identity Student Questionnaire (SISQ) were administered to the select subjects of educators and sixth grade students in Chicago, Illinois, and Gary, Indiana, schools. All students in this sampling were asked to draw self-portraits so that the in�vestigator could establish evidence of how they perceived themselves physically and whether or not Black consciousness had any effect on their self-concepts. The samples investigated consisted of 2.13 traditional school students enrolled in one Catholic and four public schools, and 91 non-traditional school students. The non- traditional schools included two Catholic schools and one independent Black Nationalist school. There was a total of 26 educators, 17 in the traditional schools and 9 non-traditional school educators. Eleven null hypotheses were tested to determine if Black consciousness, Black identity, education for Black history/ culture awareness, and family expectations affect the development of the Black self-concept. The Statistical Package for the Social Sciences(SPSS) was used to compute the data derived from the questionnaires. These hypotheses were tested by analysis of variance to show the differences between groups. For further statistical treatment, Pearson's Product- Moment Correlation Coefficient was employed to show significant differences between correlation coefficients, if there were any. In these comparisons z and t ratios were used to show significant differences. All statistics were inter-preted at the .05 level of significance. Four questions that are related to the research were posed and were included in the discussion which is based on the findings and conclusions of this study. Findings The self-portrait section presented interpretational problems not anticipated in the original design of this study; these problems indicated a need to employ standard criteria for judging the portraits that would enhance the replication of the study. The interpretative guide used in this study relied upon the degree to which the following components were presented in each drawing: Broad facial features, afro or curly hair styles, skin coloration, or how closely the portrait resembled the actual subject. The self-portraits and observations revealed that 54 percent of the traditional school students (N=213) drew themselves paradoxically different from the way they looked. In every instance the non-traditional school students drew themselves more as they really looked. The reader is cautioned in drawing conclusions from these data, or attempting broad generalizations. The interviews and observations showed differences be�tween the two groups of students. Some traditional school students evidenced low negative racial self-concept in that they did not find it a pleasant experience to be Black in an urban ghetto. The same students frequently expressed feelings that reflected a lack of parental communication regarding Black awareness. Non-traditional school students spoke positively about family expectations and education towards their Afrikan heritage. They also evidenced strong ties to Afrikan cultural influences through hair styles and dress attire. Educators showed fewer differences in their levels of Black consciousness than did the students, but the differences were important. The greatest difference between non-traditional and traditional educators was in respect to the relationship between Black identity and self-concept. Non-traditional school educators in this study, as opposed to traditional school educators, believed that these factors are inextricably related. There were no significant differences between students on any of the components in traditional and non-traditional schools with respect to the independent variables sex and age. The independent variable, school, revealed a statistically significant difference in the direction of non-traditional school students on all components except Black Identity, thus rejecting the null hypothesis for this component. The hypothesis for the component, Family Expectations, was not supported by the data on the independent variables, school and education of parents. On this component, there was a significant statistical difference favoring non-traditional school students in what their families expect of them regarding Black awareness and education from a historical perspective. The hypothesis for the statistical correlations for students was supported for all paired factors between the two groups except the paired variables of self-concept and education for Black history/ culture, which rejected this hypothesis in favor of traditional school students
The ecology of Bactrocera tryoni (Froggatt) (Diptera: Tephritdae) : what do we know to assist pest management?
No full textThe distribution, systematics and ecology of Bactrocera tryoni, the Queensland fruit fly are reviewed. Bactrocera tryoni is a member of the B. tryoni complex of species, which currently includes four named species, viz. B. tryoni s.s., B. neohumeralis, B. melas and B. aquilonis. The species status of B. melas and B. aquilonis are unclear (they may be junior synonyms of B. tryoni) and their validity, or otherwise, needs to be confirmed as a matter of urgency. While Queensland fruit fly is regarded as a tropical species, it cannot be assumed that its distribution will spread further south under climate change scenarios. Increasing aridity and hot dry summers, as well as more complex, indirect interactions resulting from elevated CO2, make predicting the future distribution and abundance of B. tryoni difficult. The ecology of B. tryoni is reviewed with respect to current control approaches (with the exception of Sterile Insect Technique which is covered in a companion paper). We conclude that there are major gaps in the knowledge required to implement most non-insecticide based management approaches. Priority areas for future research include host plant interactions, protein and cue-lure foraging and use, spatial dynamics, development of new monitoring tools, investigating the use of natural enemies and better integration of fruit flies into general horticultural IPM systems
Metabolic rate and tethered flight performance of male Bactrocera dorsalis (Hendel) (Diptera : tephritidae) fed nutritional and semiochemical supplements
No full textDissertation (MSc (Entomology))--University of Pretoria, 2024.The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is an invasive species that has rapidly spread across the African continent, endangering the security of agricultural industries. Integrated pest management tactics such as the male annihilation technique (MAT) are used to suppress B. dorsalis populations in the region. The sterile insect technique (SIT) is being investigated as a viable additional tactic after its successful implementation in other parts of the world. There is evidence to suggest that pre-release nutritional and semiochemical treatments for sterilised males can enhance their competitive performance against wild type males in SIT programmes. This project investigates the impact of a diet enriched with yeast hydrolysate (YH) and/or containing semiochemicals [either methyl eugenol (ME) or eugenol (EU)] on the resting metabolic rate (RMR), flight performance, and body condition of male B. dorsalis. Respirometry revealed that a YH inclusive diet increased average RMR whereas semiochemical feeding decreased average RMR in male B. dorsalis. The analysis of male body condition in B. dorsalis showed that a protein inclusive diet positively influenced wing loading and adult body weight. Tethered flight performance results did not suggest any significant influence on flight performance parameters by dietary or semiochemical treatments. However, the average distance flown by male B. dorsalis was significantly impacted by their recorded wing area. With results indicating that males with larger wings tended to fly farther distances on average. Lipid content analysis indicated that males consuming EU had a reduced average dry weight. These findings could be useful when implementing more climate conscious SIT programs and aid in their parallel applications with MAT programs in the future.International Atomic Energy AgencyZoology and EntomologyMSc (Entomology)UnrestrictedFaculty of Natural and Agricultural SciencesSDG-15: Life on lan
Environmental and physiological correlates of response by three fruit fly (Diptera: Tephritidae) species to commercial lures
No full textDissertation (MSc (Entomology))--University of Pretoria, 2024.Traps are important tools for managing economically damaging pest fruit flies (Diptera: Tephritidae). Trap captures help fruit and vegetable producers to monitor fruit fly populations and shape their pest management action thresholds. However, biotic, and abiotic factors influence how fruit flies respond to attractive stimuli used in traps. Physiological changes within a fly can change its resource orientated behaviours. In a similar manner, environmental changes can limit or encourage insect activity that governs this behavioural response. Consequently, baited traps only catch subsets of the population under certain weather conditions. Understanding how fruit fly lure responses change is important for improving interpretation of trap captures with direct benefits for fruit fly monitoring and management programmes. In this dissertation, I aimed to test how fruit fly physiology, the environment, and lure weathering impact lure response. I assessed the response of three economically important fruit fly species to several commercial fruit fly lures. To do this I released known numbers of flies in field cages, which enabled unambiguous measurement of the relative response of species to lures under the experimental conditions. The response of Ceratitis capitata (Wiedemann) was tested for BioLure, E.G.O PheroLure and trimedlure. The response of C. cosyra (Walker) was tested for BioLure and E.G.O PheroLure, while the response of Bactrocera dorsalis (Hendel) was measured for BioLure and methyl eugenol. For each species and lure combination, response by a group of flies (n=25) was determined in a semi-field setting in relation to sex, diet (protein deprived and protein rich), and age (two-, 10-, and 20-days post emergence). The effect of nutrient reserves (protein, lipid, and carbohydrate content), and body weight on lure response was also quantified using colorimetric biochemical assays adapted from van Hendel’s method. The environmental effects of temperature (°C), relative humidity (%RH), and light intensity (lux) on lure response were also measured. Additionally, the effects of temperature and relative humidity on the weathering of the lures BioLure, E.G.O PheroLure, methyl eugenol and Capilure (trimedlure mixed with extenders) was evaluated in a field setting. The. The weight of each lure was measured at daily intervals for 30 days to determine weight loss of each lure product in relation to daily mean temperature and relative humidity. Additionally, I tested the effect that semiochemical pre-release feeding, diet (protein rich and iii protein deprived), and age (four-, 10-, and 20-days post emergence) had on the response of B. dorsalis males (n=20) to methyl eugenol baited traps in a field cage setting. Semiochemicals were fed to flies 48 hours prior to field cage testing, with methyl eugenol, eugenol, or no semiochemicals (control) being tested. Semiochemicals were mixed into the relevant diet treatment food at a concentration of 1.5%. I further assessed the effects that body weight and total body nutrient composition (protein, lipid, and carbohydrate content) had on the response of B. dorsalis to methyl eugenol. Body nutrient composition data was obtained with the revisited van Hendel’s method which uses colorimetric biochemical assays. The effect that temperature (°C), relative humidity (%RH), and light intensity (lux) had on the response of B. dorsalis to methyl eugenol lures was also measured. Overall, the effect of fly physiology and the environment on response is specific to the species and lure tested. Despite BioLure being considered a female biased lure there was no consistent bias towards female captures. Only in C. capitata were protein deprived females more likely to respond to BioLure. Irrespective of species, access to dietary protein decreased the response to BioLure baited traps. This suggests that abundant natural sources of protein may decrease the accuracy of fruit fly monitoring that relies on BioLure as the main attractant. Age affected the response of flies to male lures. Immature C. capitata and C. cosyra responded more strongly to E.G.O PheroLure and trimedlure. However, immature B. dorsalis were the least responsive to the male lure methyl eugenol. I found that the effects of temperature on response are largely lure and species specific. The response of B. dorsalis increased at warmer temperatures irrespective of the lure tested. Similarly, the response of flies to male lures increased with temperature. However, I observed that the response of C. capitata and C. cosyra to BioLure is not affected by temperature. Warmer temperatures resulted in greater lure weight loss for all tested lures, but this occurred to varying degrees. Combining the results of lure volatilisation and fly response, I identified that the increased response of C. capitata males to trimedlure at warmer temperatures is mostly driven by increased fly activity. Whereas increased response of C. capitata and B. dorsalis to E.G.O PheroLure and methyl eugenol, respectively, at warmer temperatures coincides with greater release rates of the lures. These results show that monitoring conducted when temperatures are cooler is likely to underestimate fruit fly populations. Feeding on either methyl eugenol or eugenol reduces the response of B. dorsalis males to methyl eugenol baited traps by similar amounts. Access to dietary protein had little effect iv onthe reduced response by males to methyl eugenol when fed semiochemicals. This suggests that feeding semiochemicals to B. dorsalis males may facilitate the simultaneous application of the sterile insect technique and the male annihilation technique. Furthermore, this shows that protein supplementation will not counteract the methyl eugenol response suppression induced by pre-release semiochemical feeding. These results also show that eugenol is a promising alternative to methyl eugenol to achieve the required reduction in response to methyl eugenol. Overall, this dissertation highlights that fly physiology and the environment significantly impact the response of fruit flies to commercially used lures. Specifically, access to natural sources of protein may decrease the accuracy of trap surveys that rely on BioLure. The minimal response of flies occurring at temperatures below 12 °C indicates that trapping surveys deployed below this will largely misrepresent population sizes and are likely to miss incipient fruit fly incursions. It is thus crucial to integrate fruit fly physiology and environmental variables into fruit fly monitoring and survey programmes to increase their accuracy. My results further indicate that eugenol is an effective and safe semiochemical that can be used in joint MAT-SIT programmes. I also observed that protein supplementation and semiochemical pre-release feeding can occur simultaneously in MAT-SIT programmes without increasing the response of B. dorsalis to methyl eugenol. Overall, this dissertation highlights the complex nature of tephritid lure response and the value that quantifying and integrating these effects into monitoring and control programmes can have on fruit fly management.Citrus Research International (Project 1229) and the International Atomic Energy Agency (CRP D41027) funded this project.Zoology and EntomologyMSc (Entomology)UnrestrictedFaculty of Natural and Agricultural SciencesSDG-15: Life on lan
Dispersal and mating behaviour of Queensland fruit fly, Bactrocera tryoni(Froggatt) (Diptera: Tephritidae): Implicationsfor population establishment and control.
No full textThe Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), a major pest of horticulture in eastern Australia, is a relatively poor coloniser of new habitat. This thesis examines behavioural properties that might limit the ability of B. tryoni to establish new populations. As the potential for B. tryoni to establish an outbreak population may be most directly limited by mechanisms associated with dispersal and mating behaviour, these two factors were the focus of this research project. The relevance of dispersal and mating behaviour for control of outbreak populations was assessed. Dispersal (i) Dispersal patterns of males and females are not different. Dispersal of post-teneral male B. tryoni from a point within an orchard near Richmond, New South Wales, was monitored following temporally replicated releases. Application of sterile insect technique (SIT) requires knowledge of dispersal from a release point so that effective release rates can be determined. In addition, dispersal following introduction to new habitat can lead to low or negative population growth and an Allee effect. In Spring and Autumn, 2001 – 2003, three different strains of B. tryoni were released: (1) wild flies reared from infested fruit collected in the Sydney Basin; (2) a laboratory-reared strain with a colour mutation (white marks); and (3) sterile flies obtained by gamma-irradiation of a mass-reared strain. Dispersal was monitored using a grid of traps baited with the male attractant, cuelure. During the majority of releases, flies were massmarked using a self-marking technique and fluorescent pigment powder to enable identification of recaptured flies. A preliminary study found that fluorescent pigment marks had no effect on adult survival and marks did not fade significantly in the laboratory over a period of five weeks after eclosion. As cuelure repels inseminated sexually mature female B. tryoni, unbaited, coloured flat sticky traps, and black and yellow sticky sphere traps baited with a food lure (protein autolysate solution) were used to supplement traps baited with cuelure. The effectiveness of these two sticky trap types was assessed, and recaptures used to compare patterns of dispersal from a release point by male and female B. tryoni. Fluorescent yellow (chartreuse), green, and clear unbaited flat sticky traps were relatively ineffective for monitoring dispersal of sterile male and female B. tryoni, recapturing only 0.1% of released sterile flies. Monitoring dispersal with sticky ball traps baited with protein autolysate solution was more successful, with yellow spheres and black spheres recapturing 1.7% and 1.5%, respectively. Trap colour had no effect on recaptures on flat sticky traps or sticky spheres. Equal recapture rates on yellow and black sticky sphere traps suggests that the odour of yeast autolysate solution was more important than colour for attraction of post-teneral flies to traps. Using the results of recaptures on odoriferous black and yellow sticky sphere traps within one week of release, regression equations of male and female recaptures per trap were found to be similar (Figure 4-3). This is the first study to clearly indicate that post-teneral dispersal patterns of male and female B. tryoni released from a point do not differ, enabling the use of existing models to predict density of both sexes of B. tryoni following post-teneral dispersal. (ii) Males disperse further in Spring than in Autumn, but this is not temperature-related. Analysis of replicated recaptures in traps baited with cuelure revealed that dispersal of male B. tryoni in an orchard near Richmond, New South Wales, was higher in Spring than in Autumn (Figure 5-6). As the maximum daily temperature was significantly higher in Spring than in Autumn this result was unexpected, since earlier studies have found that B. tryoni disperse at the onset of cool weather in search of sheltered over-wintering sites. Dispersal of post-teneral B. tryoni may have been affected by habitat suitability; it was found that seasonal trends in dispersal could have been influenced by local habitat variables. Low mean dispersal distances in Autumn may be explained by the presence of fruiting hosts in the orchard, or the availability of resources required by over-wintering flies. There was no significant correlation between temperature and mean dispersal distance, suggesting that higher rates of dispersal cannot be explained by temperature-related increases in activity. Recapture rate per trap was significantly negatively correlated with increasing daily maximum and average temperature. This may have consequences for detection of B. tryoni outbreaks in quarantine areas due to reduced cuelure trap efficiency. (iii) Maturity and source variation affect dispersal and response to cuelure. This research indicated that most male and female B. tryoni do not disperse far from a release point, suggesting that an invading propagule would not spread far in the first generation. However, there is considerable variation in flight capability among individuals. Comparison of wild, laboratory-reared white marks, and gamma-irradiated sterile male B. tryoni indicated that mean dispersal distance and redistribution patterns were not significantly affected by fly origin. Despite no difference in dispersal distance from the release point, recaptures of wild and sterile males per Lynfield trap baited with cuelure were highest within one week after release, whereas recaptures of white marks males per trap increased in the second week. This result may offer evidence to support the hypothesis that sterile male B. tryoni respond to cuelure at an earlier age. Rearing conditions used to produce large quantities of males for sterilisation by gamma-irradiation may select for earlier sexual maturity. Mating Behaviour (i) Density and sex ratio do not affect mating, except at low densities. Demographic stochasticity in the form of sex ratio fluctuations at low population density can lead to an observed Allee effect. The effect of local group density and sex ratio on mating behaviour and male mating success of a laboratory-adapted strain of B. tryoni was examined in laboratory cages. In the laboratory-adapted strain of B. tryoni used in this study, a group of one female and one male was sufficient for a good chance of mating success. The proportion of females mated and male mating success was not significantly affected by density or sex ratio, although variability in male mating success was higher at low density. This could indicate that mating success of B. tryoni can be reduced when local group density is low owing to decreased frequency in encounters between males and females. (ii) Mass-reared males exhibit aberrant mating behaviour, but this does not reduce mating success. Strong artificial selection in mass-rearing facilities may lead to decreased competitiveness of sterile males released in SIT programs as a result of alteration or loss of ecological and behavioural traits required in the field. The effects of domestication and irradiation on the mating behaviour of males of B. tryoni were investigated by caging wild, mass-reared and sterile (mass-reared and gammairradiated) males with wild females. Mating behaviour of mass-reared males was different from that of wild males, but behaviour of wild and sterile males was similar. Mass-reared males were found to engage in mounting of other males much more frequently than wild and sterile males, and began calling significantly earlier before darkness. Male calling did not appear to be associated with female choice of mating partners, although this does not exclude the possibility that calling is a cue used by females to discriminate between mating partners. Conditions used to domesticate and rear large quantities of B. tryoni for SIT may select for an alternative male mating strategy, with mass-reared males calling earlier and exercising less discrimination between potential mating partners. Despite differences in behaviour of wild, mass-reared and sterile males, frequency of successful copulations and mating success were similar. (iii) Pheromone-calling by males was increased in larger aggregations but this did not result in significantly more female visits. Finally, large laboratory cages with artificial leks were used to investigate the importance in B. tryoni of male group size for female visitation at lek sites and initiation of male pheromone-calling. Calling propensity of male B. tryoni was increased by the presence of conspecific males. Females visited the largest lek more frequently than single males, but there was no correlation between lek size and female visitation. Female B. tryoni had a limited capacity to perceive a difference between the number of calling males; female visitation at leks was only weakly associated with male calling, suggesting that lek size and the number of pheromone-calling males may not be the only factor important in locating mates in B. tryoni. The weak, but positive correlation between male calling and female visitation may indicate that passive attraction maintains lek-mating in B. tryoni. Further studies are essential on mating behaviour of B. tryoni, including identification of male mating aggregations in the field, measurement of habitat variables associated with male aggregations, the influence of density on wild B. tryoni mating success, and the role of pheromone-calling, in order to optimise use of SIT for control of this pest
Cellular- and symbiont-mediated defenses in Bactrocera dorsalis (Hendel) and Ceratitis cosyra (Walker) against their native and introduced parasitoids
No full textThesis (PhD (Zoology))--University of Pretoria, 2024.The use of parasitoids as pest biological control agents has been adopted globally.
Nonetheless, the success of parasitoid-oriented biological control programs is dependent on the virulence of the parasitoid, a phenomenon that is influenced by several host (pest) and parasitoid-associated factors. Common among the host factors are host innate (i.e., cellular, and humoral) immune defences and host-associated bacterial symbionts. Host innate immunity, through regulating encapsulation and melanisation of the parasitoid egg, has been shown to influence host-parasitoid dynamics. Additionally, bacterial symbionts through immunomodulation, competition for nutrients, and releasing toxins, affect the development and fitness of the parasitoids. However, in the oriental fruit fly, Bactrocera dorsalis (Hendel) and the marula fruit fly, Ceratitis cosyra (Walker) (both Diptera: Tephritidae), common pests of fruticulture, the effect of host immunity on the outcome of their interaction with parasitoid wasps is unknown. Moreover, several B. dorsalis-associated symbionts are known to affect the development, reproduction, pesticide resistance, and susceptibility of this pest to entomopathogenic fungi. Nonetheless, the effect of larvae-associated gut symbionts on the outcome of the interaction between B. dorsalis and its associated parasitoid wasps is unknown.
The egg-prepupal parasitoid, Fopius arisanus (Sonan) and the larval-pre-pupal parasitoid, Diachasmimorpha longicaudata (Ashmead) (both Hymenoptera: Braconidae) and are the most common parasitoid wasps used as biological control agents of B. dorsalis, globally. Additionally, since its invasion and detection in Africa, some native parasitoids, such as the larval-prepupal parasitoid, Psyttalia cosyrae (Wilkinson) (Hymenoptera: Braconidae) has been investigated as a potential biological control agent of this pest and its native counterpart, C. cosyra. Diachasmimorpha longicaudata and F. arisanus successfully develop in B. dorsalis and C. cosyra whereas P. cosyrae develops in C. cosyra but not in B. dorsalis. This is suggestive of possible differences in defence mechanisms of B. dorsalis and C. cosyra against these parasitoids, a phenomenon that could be attributed to host intrinsic factors e.g., cellular immunity and host-associated microbes that enable the pests to defend themselves against some parasitoids and not others. Moreover, the differences in wasp performance could be due to variations in parasitoid virulence. This thesis investigated the cellular immune responses of C. cosyra and B. dorsalis to parasitoids, the impact of parasitisation on B. dorsalis gut microbiota, as well as the effects of B. dorsalis-associated larval gut symbionts on parasitoid development and their consequences for parasitoid offspring fitness.
To evaluate the role of cellular immune defences on the outcome of host-parasitoid interactions in B. dorsalis and C. cosyra, I investigated the melanotic encapsulation responses, total and differential hemocyte counts, hemocyte viability, and hemocyte spreading ability in the fruit flies after parasitisation by D. longicaudata and P. cosyrae. The adult fly emergence rate post-parasitisation was also recorded. I found stronger immune responses in B. dorsalis, mediated by a higher haemocyte load enabled this pest to mount effective melanotic-encapsulation responses against D. longicaudata and P. cosyrae than in C. cosyra. Furthermore, D. longicaudata was more efficient than P. cosyrae at suppressing host-immune defences, especially by reducing hemocyte spreading and the proportion of viable hemocytes in both host fruit flies. This was corroborated by the low encapsulation rates of this parasitoid and the consequential higher number of emerging D. longicaudata adults compared to P. cosyrae. These results reveal that D. longicaudata is a more efficient parasitoid wasp and can be used as a biological control agent of C. cosyra and B. dorsalis.
Using next generation amplicon sequencing, parasitoid-mediated perturbations on the B. dorsalis gut microbiota were investigated in response to parasitisation by D. longicaudata and the native counterpart, P. cosyrae. My results showed that, parasitisation shaped the composition, abundance, and diversity of the bacterial and fungal communities of B. dorsalis. Parasitisation by P. cosyrae had no effect on the gut microbial diversity of B. dorsalis larvae. On the other hand, D. longicaudata induced dysbiosis in the guts of B. dorsalis larvae and increased the abundance of pathogenic bacteria genera such as Stenotrophomonas, Serratia and MorganelIa. Diversity and abundance of the fungi community of B. dorsalis were negatively affected by parasitisation by both parasitoid species.
Furthermore, I investigated the impact of some B. dorsalis gut symbionts on the acceptability of B. dorsalis (axenic, symbiotic, or the bacteria mono-associated lines) by parasitoids, adult parasitoid emergence, and the fitness of parasitoid offsprings. I found that Lactococcus lactis, a common gut symbiont of this pest, increased the number of F. arisanus and D. longicaudata emerging from B. dorsalis. This bacterium also increased the fitness of the F1 parasitoid offspring. In contrast, Providencia alcalifaciens, reduced the proportion of emerging parasitoid wasps but increased F1 wasp fitness parameters such as size and fecundity.
The findings of my thesis contribute to our understanding of the underlying physiological factors influencing parasitoid performance and their implications for the management of the frugivorous pest, B. dorsalis. This thesis has also identified a candidate symbiont, L. lactis that can be incorporated as a probiotic during mass rearing of the potent parasitoids, D. longicaudata and F. arisanus. This could potentially increase the number and fitness of the mass-reared parasitoids hence contributing to the development of a sustainable biological control programme against B. dorsalis.The German Academic Exchange Service (DAAD) through the African Regional Postgraduate Programme in
Insect Science (ARPPIS).
The International Development Research Centre (IDRC) and the Australian Centre for International Agricultural Research (ACIAR) (grant number 109040)
The Norwegian Agency for Development Cooperation (NORAD), and the Section for Research, Innovation, and Higher Education (grant number RAF-3058 KEN-18/0005)
The German Agency for International Cooperation (grant number 81298148)Zoology and EntomologyPhD (Zoology)UnrestrictedFaculty of Natural and Agricultural SciencesSDG-01:No povertySDG-02:Zero HungerSDG-13:Climate actionSDG-15:Life on lan
Two Depressions, One Banking Collapse
No full textThe depression of the 1890s in Australia was associated with the collapse of the banking system, whereas problems in the financial system during the 1930s depression were far less severe. This is despite the fact that the initial macroeconomic shock during the 1930s depression was at least as large as that during the 1890s depression. We show that variation in the performance of the financial sector during the two depressions was due to differences in the condition of the financial sector well before each depression. Differences in real external factors and government policies were not sufficient to explain variation in the performance of the financial sector.Australian economic depressions; financial instability; banking crises
Investigating the effect of micro-quadcopter flight on UAS instruction
No full textThis paper examines student perceptions of micro-quadcopter flights in a higher education setting through a case study format. The purpose of the flight activity discussed is to allow students to familiarize themselves with quadcopter flight characteristics, as early as possible, at their own pace in a low stress environment. Through a series of interviews with students who had taken a course where this activity was performed it was found that students enjoyed the activity and found it engaging. Some students felt that the activity provided them confidence for later courses, and many felt that it helped teach basic quadcopter control. It was also found that if the activity is repeated in later courses it should include some form of directed activity, instead of focusing on “free flight”. Several students brought up another activity in the course, simulator flights, and these are briefly discussed. Future work should look to find if these activities have a positive effect on student flight performance
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