The impact of a primary infection with the incompatible digenean Plagiorchis elegans to groups composed of young, juvenile and adult Biomphalaria glabrata and a challenge infection with the compatible parasite Schistosoma mansoni was examined. Egg production of young B. glabrata was significantly reduced by P. elegans at the higher exposures of 16 eggs per snail, while egg production of adult B. glabrata was reduced at exposures of 8 and 16 eggs per snail. Egg production of juvenile B. glabrata snails was not significantly affected by any of the levels of P. elegans exposures. The survivorship of juvenile B. glabrata snails was significantly lowered by an exposure to 16 P. elegans eggs per snail. The survivorship of adult snails was significantly reduced by exposures to both 8 and 16 P. elegans eggs per snail. Interestingly enough, the survivorship of young B. glabrata snails was not significantly affected by P. elegans exposure. Snails harboring small P. elegans infections acquired a resistance to Schistosoma mansoni infection. Infection with P. elegans did not have any significant effect on the egg production of the young and adult sympatric snails, Helisoma trivolvis trivolvis. The survivorship of adult H. trivolvis trivolvis was not significantly affected by exposure to P. elegans. This being said, young H. t. trivolvis that were exposed to P. elegans had a higher survivorship than did control snails. Exposed Bulinus truncatus snails laid up to 50% fewer eggs for the first five weeks due to P. elegans infection. There was however no effect on the survivorship of the snails.

The potential of Smicronyx umbrinus Hustache and Smicronyx guineanus Voss (Coleoptera: Curculionidae) as biocontrol agents of Striga hermonthica (Del) Benth was investigated at both population levels of Striga and Smicronyx spp. in the field in Burkina Faso. High population levels of Smicronyx spp. resulted in higher percentages of seed-pod galls although the weevils' adult populations decreased during S. hermonthica seed capsule production. Smicronyx spp. were observed galling Striga aspera (Willd) Benth capsules ca. 60 days before S. hermonthica emerged in sorghum fields. The weevils also galled S. hermonthica stems at soil level and Sm. umbrinus was found to be the main species causing this symptom. Smicronyx spp. also galled Alectra vogelii Benth stems, Smicronyx dorsomaculatus Cox being the main species attacking this parasitic weed. Another Smicronyx species not yet described was collected on A. vogelii. Stem galls appeared to be more effective nutrient sinks than fruit galls. The weevils alone did not have sufficient impact to be considered successful biocontrol agents for S. hermonthica but they could contribute to an integrated control strategy against Striga. Smicronyx spp. have a good potential as biocontrol agents for A. vogelii.

Thirty-two isolates of rhizosphere bacteria, selected for their ability to inhibit zoospore germination and/or mycelial growth of Pythium aphanidermatum (Pa) in vitro, were evaluated in a test tube bioassay using cucumber c.v. 'Straight 8'. These isolates were identified as Psedudomonas corrugata (Pc13 or 35) and P. fluorescens (Pf15, 16 or 27). All but one of the five isolates effectively colonised the roots of cucumber plants in short term studies. Isolates 15 and 35 were found to maintain high population densities throughout the time period. Pa-inoculated plants treated with the Pc13 or Pf15 produced fruit yields equal to 92 and 74% respectively of the control (no Pa, no bacteria). Pa-inoculated plants without bacteria yielded only 46% of the control. In the fall crop, Pa-inoculated plants treated with Pc13 or Pf15 yielded 52 and 47% of the control compared to Pa-only treatment, which yielded 12.5% of the control. In both crops, treatment with any of the bacterial isolates resulted in significantly reduced cull rates compared to the Pa-only treatment.

The use of a biofungicide on the perfect stage of V. inaequalis on leaf litter is one potential way to reduce the number of fungicides used to control apple scab. The previous in vitro screenings of Quebec mycoflora have shown that several isolates are able to significantly reduce the primary inoculum of the pathogen. Among the screened fungi, P176A and P130A, reduced over 98% of the ascospore production and were as effective as Athelia bombacina. However, because in vitro tests are generally poor predictors of in vivo assays a re-evaluation of the antagonists was done under field conditions. Eight fungal isolates, leaf shredding, and two comparative treatments (A. bombacina, 5% urea) were applied to intact scabbed leaves in October 1994 and 1995. After the treatments, the leaves overwintered on the orchard ground until the next spring. In April, samples of treated leaves were randomly selected and placed in spore traps to collect the ejected ascospores during rainfall. Since the primary inoculum was ejected during a four-month period, antagonism was based upon ratings taken throughout the whole ejection season. To evaluate the effect of incubation conditions on the antagonistic performance we incubated separately, in vitro and in vivo, sterile leaf disks which were artificially inoculated with V. inaequalis and fungal isolates. (Abstract shortened by UMI.)

Soybean (Glycine max (L.) Merr.) is one the major crops produced worldwide. However, soybean is susceptible to many diseases. Sclerotinia stem rot (SSR) disease caused by Sclerotinia sclerotiorum (Lib.) de Bary is considered one of the most important fungal diseases of soybean. It can be controlled by chemicals (e.g. fungicides), by breeding cultivars with disease resistance and by cultural control (e.g. increasing the width between rows, reducing plant populations). A promising and complementary method of controlling SSR disease in the field is the application of biological control agents. Biological control agents introduced in a soil environment will interact with other soil food web organisms, as do the pathogenic organism and infected plants, which may change the genetic and functional diversity in soil microbial communities. Profiling these changes may lead to an improved understanding of the interactions between these players (biological control agents, pathogens, soil biota and plants) in the biological control phenomenom, permiting us to exploit naturally-occurring ecological relationships and develop more sustainable approaches to control soybean diseases. Fatty acid biomarkers analysis was used to profile microbial communities in soils. Two laboratory studies were conducted to evaluate the methods used for extraction and profiling the fatty acid biomarkers from soil samples with a range of soil properties (clay content, organic matter content), The first study investigated the best solvent mixture for recovering fatty acid biomarkers from soil using an automated pressurized solvent extraction (PSE) system. Solvent mixtures containing chloroform and methanol were more efficient at extracting fatty acids from agricultural soils than hexane:2-propanol and acetone. The second study presented an exploratory pyrolysis-mass spectrometry technique to rapidly fingerprint soil lipids extracted from different agroecosystems. Pyrolysis-mass spectrometry discriminated among soils and crop production systems in the same way as the fatty acid profiling. I also report on the efficicacy of biological control agents to control Sclerotinia stem rot disease in soybean. A two-year study was conducted in soybean fields under conventional or no tillage to determine whether Trichoderma virens (SoilGard(TM)) and arbuscular mycorrhizal fungi (a mixture of Glomus intraradices and G. mosseae ), used alone or in combination, could reduce sclerotinia stem rot (SSR) disease incidence. Generally, SSR disease indicators, as well as the soybean yield, were not affected significantly by the biological control treatments. I then studied whether changes in microbial community composition were related to the inoculation of the biological control agents and the disease incidence in soybean fields. Inoculation of biological control agents changes the expression of many soil fatty acids during both years of the trial. Also, in the plots with severely diseased plants, fatty acids biomarkers of gram positive and actinomycetes bacteria were significantly greater than in plots with healthy plants. I conclude that further improvement in laboratory techniques and procedures will permit researchers to efficiently extract and characterize soil lipids, providing new insight into soil organic matter dynamics and soil microbial ecology. Further study will be needed to verify the efficacy and optimize the application method, dose and timing of biocontrol agents to provide protection against SSR disease in soybean fields.

Addendum in pocket. / Biblography: leaves 162-173. / v, 177, [5] leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Phytophagous sucking insects, aphids in particular, are common pests of plants. These insects secrete salivary enzymes into their food material. One plant defence mechanism is the induction and/or accumulation of deterrent phytochemicals. In the present study, a model enzyme system was chosen to mimic the oxidative activity of insect saliva. Isolation and sructural identification of the products of plant allelochemicals was achieved for several substrates. Insects were also exposed to individual plant chemicals in feeding "choice" tests. Preliminary examinations suggest that plants containing increased levels of phenolic allelochemicals show correlated increases in resistance to attack by aphids. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1996

Este trabalho objetivou isolar leveduras capazes de produzir e excretar a toxina killer a partir de frutos tropicais, para atuarem no controle biolÃgico de fitopatogenos em pÃs-colheita. Inicialmente, foram isoladas 580 leveduras a partir de 87 amostras de frutos tropicais (mamÃo, caju, sapoti, murici, manga e acerola), dentre as quais 29 exibiram o fenÃtipo killer. Todas as cepas killer foram identificadas pelo sequenciamento da regiÃo D1/D2 do 28S rRNA, em que ficou demonstrada a presenÃa de Candida aaseri, Wickerhamomyces anomalus, Pichia kluyveri, Meyerozyma guilliermondii, Kodamaea ohmeri. Cinco leveduras foram capazes de inibir em 100% a germinaÃÃo de conÃdios em meio lÃquido e reduzir o crescimento micelial, em meio sÃlido de Colletotrichum gloeosporioides in vitro, com destaque para M. guilliermondii (cepa 443) que foi capaz de reduzir o crescimento micelial do fitopatogeno em 60% em meio sÃlido. As duas leveduras com melhores resultados in vitro foram testadas in vivo, contra C. gloeosporioides, agente da antracnose em pÃs-colheita de mamÃo e outros frutos tropicais, W. anomalus (cepa 422) e M. guilliermondii (cepa 443). TambÃm foi investigada a ocorrÃncia de micoparasitismo como mecanismo de aÃÃo do antagonista por meio de microscopia eletrÃnica de varredura â MEV e detecÃÃo das enzimas hidrolÃticas, quitinase e β-1-3 glucanase. Os resultados demonstraram que, quando aplicada simultaneamente ao fitopatÃgeno e incubadas em cÃmara Ãmida (95% U.R.) a 28 ÂC, as leveduras W. anomalus (cepa 422) e M. guilliermondii (cepa 443) foram capazes de reduzir a ocorrÃncia da doenÃa em 24,62%, 7,0% e 20,68%, respectivamente, atà 06 dias apÃs a inoculaÃÃo. Verificou-se que o tempo de inoculaÃÃo da levedura teve significativa influÃncia sobre sua aÃÃo antagonista; a aplicaÃÃo dos agentes com 24 ou 12 horas de antecedÃncia em relaÃÃo ao fitopatÃgeno resultou em reduÃÃo de 30% e 13,75% para W. anomalus (cepa 422), em 40% e 35% para W. anomalus (cepa 440) e em, 41,17 e 31,35% para M. guilliermondii (cepa 443) respectivamente. A ocorrÃncia de micoparasitismo foi confirmada atravÃs de eletromicrografias que evidenciaram a uniÃo das leveduras Ãs hifas do C. gloeosporioides, provocando, em alguns casos, perda de turgidez e atà ruptura dessas; tudo isso associado à produÃÃo de β 1-3-glucanase. As leveduras killer, W. anomalus (cepa 422) e M. guilliermondii (cepa 443) que apresentaram melhores resultados nos testes in vivo foram testadas associaÃÃo com cinco diferentes veÃculos de aplicaÃÃo na proteÃÃo em pÃs-colheita de mamÃo. ApÃs 90 dias de incubaÃÃo a 4 ÂC, essas leveduras mantiveram-se viÃveis em todos os veÃculos de aplicaÃÃo testados e durante todo o perÃodo de incubaÃÃo, frutos tratados com formulaÃÃes (leveduras + veÃculos de aplicaÃÃo) apresentaram incidÃncia de doenÃa, pelo menos 30% menores, quando comparadas aos frutos nÃo tratados. Para W. anomalus (cepa 422), o tratamento que utilizou amido (2%) reduziu em 48,3% a ocorrÃncia de doenÃas, jà para M. guilliermondii, (cepa 443), os tratamentos mais eficientes no controle da doenÃa foram os que utilizaram gelatina e cera lÃquida de carnaÃba (2%) como veÃculos de aplicaÃÃo, ambos foram capazes de reduzir em 50% a ocorrÃncia de doenÃas em pÃs-colheita de mamÃes. Eletromicrograficas revelaram que todos os veÃculos de aplicaÃÃo foram eficientes em permitir a fixaÃÃo das leveduras na superfÃcie do fruto. Leveduras killer podem atuar no biocontrole em pÃs-colheita de mamÃo e estes microrganismos atuam atravÃs de uma variedade de mecanismos de aÃÃo, o que potencializa seu efeito protetor e amplia sua eficiÃncia de aÃÃo. / This study aimed to isolate yeast able to produce and excrete the toxin from killer tropical fruits, to act in the biological control of plant pathogens in postharvest. A total of 580 yeasts strains, isolated from Ceara State of Brasil, were evaluated for their ability to produce killer toxin. Of these strains, 29 tested positive for the killer phenotype and were further evaluated for their ability to control Colletotrichum gloeosporioides germination in vitro. All yeast strains that expressed the killer phenotype were characterized by sequencing the D1/D2 regions of the large subunit of the rRNA gene. Five yeast strains provided a significant reduction in mycelial growth and conidial germination of C. gloeosporioides in vitro, especially Meyerozyma guilliermondii, which was able to reduce the fungal mycelial growth on solid medium (PDA) by 60% and block 100% of conidia germination in liquid media (PDB). Filtering and autoclaving the liquid cultures had no effect on the growth of the pathogen. These results indicate the potential use of antagonist yeasts isolated from tropical fruits in the control of anthracnose caused by C. gloeosporioides in papaya. Further elucidation of main mechanisms involved on anthracnose control by these yeasts could be helpful for the development of biocontrol techniques related to the management of this disease in tropical fruits. The efficiency of two killer yeast strains, with better results in vitro were tested in vivo against C. gloeosporioides, Wickerhamomyces anomalus (strain 422) and Meyerozyma guilliermondii (strain 443), as biocontrol agents against C. gloeosporioides, a postharvest anthracnose agent of papaya and other tropical fruits, was assessed. These strains were previously selected through in vitro assays, but in the present study, their in vivo action was assessed. In addition, the influence of phytopathogen inoculation time on the fruit in combination with the use of the biocontrol agent was also assessed. Through the use of scanning electron microscopy (SEM), we assessed mycoparasitism as an antagonistic mechanism of action. In addition, two hydrolytic enzymes, chitinase and β-1, 3 glucanase, were assayed. Our results indicated that W. anomalus (strain 422) and M. guilliermondii (strain 443) reduced the disease occurrence by 24.62% and 20.68%, respectively, for up to 6 days after inoculation, when applied 3 hours before the phytopathogen and incubated in a wet chamber (95% relative humidity) at 28ÂC. The time of yeast inoculation had a significant effect on its antagonistic action. Application of the yeasts 12 or 24 hours before the phytopathogen inoculation resulted in 13.75% and 30% of disease reductions for W. anomalus (strain 422) and 31.35% and 41.17% reductions for M. guilliermondii (strain 443), respectively. Electron micrographs confirmed mycoparasitism by clearly indicating the interaction of the yeasts with C. gloeosporioides hyphae, causing, in some cases, a loss of turgor and yeast penetration of walls with marked concavity formation on hypha cell walls. The efficiency of two killer yeasts, Wickerhamomyces anomalus (strain 422) and Meyerozyma guilliermondii (strain 443), which showed better results in tests in vtro and in vivo, associated with five different application vehicles was assessed for the protection of papayas postharvest. In this study, after 90 days of incubation at 4ÂC, W. anomalus (strain 422) and M. guilliermondii (strain 443) were viable with all application vehicles tested. Fruits treated with different formulations (yeasts + application vehicles) had a decreased incidence of disease (by at least 30%) compared with untreated fruits. The treatment of W. anomalus (strain 422) + 2% starch lowered disease occurrence by 48.3%. The most efficient treatments using M. guilliermondii (strain 443) were those with 2% gelatin or 2% liquid carnauba wax, both of which reduced anthracnose by 50% in postharvest papayas. Electron micrographs of the surface tissues of the treated fruits showed that all application vehicles provided excellent adhesion of yeast to the surface. The formulations based on starch (2%), gelatin (2%) and carnauba wax (2%) were the most efficient at controlling fungal diseases in postharvest papayas

The life-history and infection parameters of the entomopathogenic nematodes Steinernema feltiae (Filipjev)(Nematoda:Rhabditida) and Heterorhahditis megidis (Poinar, Jackson & Klein)(Nematoda:Rhabditida) were examined to provide specific details for the construction of mathematical SI models for biological control of soil insect pests. Laboratory experiments using the Greater Waxmoth, Galleria mellonella as the model host were undertaken to specifically examine the transmission behaviour of infective juvenile nematodes. The proportion of infective juveniles of S. feltiae which infected hosts was dependent on time. Previous studies declared that the proportion of infective juveniles which can infect is static, however, over a period of 5 days most of the infective juveniles infected hosts, demonstrating that the proportion infecting is dynamic. Infection of hosts by both species of nematode was compared using two mathematical representations of the transmission rate. Whereas the most parsimonious form of transmission for H. megidis was the linear Mass Action function, it was evident that, when measured at the individual nematode scale, S. feltiae transmission was non-linear. I postulated that this functional difference is due to the biology of the two species of nematodes. The subsequent effect of including the non-linear response on model predictions were investigated and it was demonstrated that the dynamics of the host nematode interaction became less stable. Spatial models of S. feltiae infection were parameterised from laboratory experiments, and control prediction of these models examined. The horizontal rate of dispersal through sand columns was determined in the presence and absence of hosts. Infective juveniles were found to disperse preferentially towards hosts. The predicted dynamics of pest control using the spatial moqel were highly dependent on the degree of nematode dispersal, host dispersal and the attraction of nematode infective juveniles towards hosts. The overall findings of this thesis have been placed in the context of epidemiological models created elsewhere, and predict that entomopathogenic nematodes may be targeted to specific pest systems with a high degree of success. An understanding of the infection biology of these nematode species is crucial in determining how and when pests may be controlled, and equally importantly, which systems successful control is not predicted.

This thesis investigates aspects of the community ecology of rabbit parasites with particular emphasis upon the gut helminths, utilising a 23 (later extended to 26) year time series of rabbits and their parasites. A clearer understanding of parasite communities can lead to more effective biological control strategies. Rabbits are regarded as a serious pest species throughout Europe and the Antipodes and the use of the myxomatosis virus, as a biological control agent, has already been tried and failed. However, a clearer picture of the parasite community may offer future possibilities for control. Additionally, the rabbit is a good model for other grazing species, as it carries a similar gut helminth community. Drug resistance is an increasing problem in a wide range of parasites. A clearer appreciation of parasite communities could also aid in the search for effective and environmentally sound pathogen control strategies (e.g. via cross immunity or competition with benign species). Theoretical models have revealed the importance of aggregation to the stability of the host parasite relationship, to parasite evolution and to interspecific parasite interactions. A number of models have considered the effect of varying aggregation upon these dynamics with differing outcomes to those where aggregation was a fixed parameter. Here the stability of the distribution for each of the rabbit helminths was examined using Taylor's power law. The analyses revealed that aggregation was not a stable parameter but varied with month, year, host sex, host age, and host myxomatosis status. Evidence for the existence of interspecific parasite interactions in natural systems has been equivocal. Factors influencing parasite intensity were evaluated for the gut helminth. A network of potential interactions between the parasites was revealed. Only month was shown to be of greater influence on the community. Following, from the above analyses, a community model was constructed which incorporated both seasonal forcing and interspecific parasite interactions, with interaction mediated via host immunity. One unexpected emergent property was an interaction between the seasonality and the immune decay rate with slower immune decay resulting in a shift of the immune response out of phase with the species against which it was produced. The model was also used to assess the potential effects of two control strategies, an anticestodal and a single species vaccine. The vaccine had greater effects on the whole community than the anticestodal because of the immune- mediated interactions. The host is also an integral part of the community as the parasite dynamics are linked with that of their host. Therefore an assessment of the parasites' impact upon host condition and fecundity was also undertaken. This revealed a variety of positive and negative associations between the parasites and their host, with potential implications for future host control strategies. This study has shown that ignoring parasite-parasite or parasite-host interactions and interactions of both the host and the parasite with the external environment, could result in a poor description of the community dynamics. Such complexities need to be considered and incorporated into theory if future control strategies for either host or parasites are to be effective.

Cryptophlebia leucotreta is an economically important agricultural pest throughout Sub-Saharan Africa. CrleGV has been considered as an alternative to chemical control of this pest due to its host specificity and innocuous nature towards vertebrates. A CrleGV free laboratory colony of C. leucotreta would be useful for the isolation of genotypically pure strains of the CrleGV and for virulence comparisons between isolates. It is preferable to have a full characterisation of CrleGV prior to its registration and release into the environment as a biopesticide. A laboratory colony of C. leucotreta, set up at Rhodes University, containing a low level of infection indicated that CrleGV is vertically transmitted. To establish a virus free laboratory colony of C. leucotreta, a solution of 3.5% sodium hypochlorite and 1% Tween 20 was used to surface decontaminate C. leucotreta eggs for removal of transovum CrleGV from the laboratory colony. No apparent infection by CrleGV was induced by subjecting larvae to stress. PCR of DNA extracted from larvae using CTAB failed to detect virus in the laboratory colony. This detection protocol was able to detect down to 60 fg (480 genome copies of CrleGV). The possibility of low-level virus remaining in the colony requires monitoring of genotypic purity of virus manipulated in the colony. Sequencing of Bam HI/KpnI fragments produced a preliminary sequence of the granulin region of CrleGV. This preliminary sequence supports the trend that the gene organisation of the granulin region of the granuloviruses infecting the family Tortricidae is conserved.