O Huanglongbing (HLB) é uma das mais temidas doenças da citricultura mundial, associada a bactérias do gênero Candidatus Liberibacter, que foram detectadas no Brasil em 2004. Em 2008, detectou-se outra bactéria associada a sintomas de HLB no Estado de São Paulo, que foi caracterizada como sendo um fitoplasma do grupo 16 SrIX. Fitoplasmas são molicutes fitopatógenos restritos ao floema de plantas, disseminados por insetos vetores. O presente trabalho buscou identificar cigarrinhas potencialmente vetoras do fitoplasma associado ao HLB e plantas hospedeiras desses insetos, bem como desenvolver uma técnica de quantificação de DNA desse patógeno em insetos e plantas. Amostragens de cigarrinhas foram realizadas quinzenalmente por 12 meses em dois pomares de laranja com histórico de ocorrência do fitoplasma 16SrIX na região norte do Estado de São Paulo, usando-se armadilhas adesivas amarelas em duas alturas (0,3 e 1,5 m) da copa de árvores cítricas, e rede de varredura na vegetação espontânea. Dados faunísticos identificaram uma espécie de Agalliinae (Agallia albidula Uhler) e três de Deltocephalinae, [Balclutha hebe (Kirkaldy), Planicephalus flavicosta (Stål) e Scaphytopius (Convelinus) marginelineatus (Stål)], como os cicadelídeos (Hemiptera: Cicadellidae) mais abundantes e frequentes nas áreas estudadas. Essas espécies predominaram na amostragem com rede de varredura e na menor altura de coleta com armadilhas adesivas, indicando comportamento de alimentação em vegetação rasteira. Com observações visuais, verificou-se associação das espécies com certas plantas invasoras, e influência da composição florística da vegetação rasteira sobre a abundância das cigarrinhas. S. marginelineatus e P. flavicosta ocorreram com maior frequência em Sida rhombifolia L. e Althernantera tenella Colla, respectivamente, enquanto que A. albidula foi predominante em Conyza bonariensis (L.) Cronq., e B. hebe ocorreu exclusivamente em gramíneas, principalmente Panicum maximum Jacq.. Plantas invasoras amostradas nas áreas foram testadas para a presença do fitoplasma 16SrIX, porém sem resultados positivos. No entanto, amostras de campo da cigarrinha S. marginelineatus foram positivas por PCR e sequenciamento para o referido fitoplasma. Indivíduos de S. marginelineatus criados em laboratório e mantidos por um período de acesso à aquisição de 72 h em citros infectado com o fitoplasma 16SrIX, foram capazes de transmití-lo para citros, após 21 dias de latência, porém com baixa eficiência (0,5%). Por meio de PCR quantitativo desenvolvido para esse fitoplasma, verificou-se baixo título do patógeno tanto em S. marginelineatus, quanto em plantas cítricas infectadas, o que pode explicar, pelo menos em parte, a baixa eficiência de transmissão pelo inseto tendo citros como fonte. Isto sugere a existência de outros hospedeiros mais adequados como fontes de inóculo para aquisição do fitoplasma por S. marginelineatus ou outro vetor ainda desconhecido. / Huanglongbing (HLB) is a severe citrus disease associated to phloemlimited bacteria in the genus Candidatus Liberibacter, which were detected in Brazil in 2004. In 2008, another bacterium was found in association with HLB symptom in the São Paulo State, and characterized as a phytoplasma belonging to 16SrIX group. Phytoplasmas are vector-borne phytopathogenic mollicutes that inhabit plant sieve elements. The goals of this study were to identify potential leafhopper vectors of the HLB-associated phytoplasma and their host plants, as well as to establish a real-time PCR procedure for pathogen quantification in vectors and plants. Leafhoppers were sampled fortnightly for 12 months by yellow sticky cards placed at two heights (0.3 and 1.5 m) on the citrus tree canopy and by sweep net in the ground vegetation of two sweet orange groves with history of infection by the 16SrIX phytoplasma, in the northern region of São Paulo State. Faunistic analyses indicated 1 Agalliinae (Agallia albidula Uhler) and 3 Deltocephalinae [Balclutha hebe (Kirkaldy), Planicephalus flavicosta (Stål) e Scaphytopius (Convelinus) marginelineatus (Stål)] species that were the most abundant and frequent leafhoppers (Hemiptera: Cicadellidae) in the experimental areas. These species predominated in sweep net and in sticky traps catches at 0.3 m above soil, showing that they inhabit the ground vegetation. Visual observations indicated a strong association of leafhopper species with some weeds and the influence of weed species composition on leafhopper abundance in the ground vegetation. S. marginelineatus and P. flavicosta were more frequent on Sida rhombifolia L. and Althernantera tenella Colla, respectively, while A. albidula was observed more often on Conyza bonariensis (L.) Cronq., and B. hebe occurred solely on grasses, more abundantly on Panicum maximum Jacq. Fourteen weed species sampled in the area were PCR tested for infection by the 16SrIX phytoplasma, but none was found infected. Nevertheless, 3 out of 30 field-collected samples (10 adults per sample) of S. marginelineatus tested positive for this phytoplasma by PCR and sequencing. Healthy lab-reared adults of S. marginelineatus were able to transmit inefficiently (0,5%) the 16SrIX phytoplasma to healthy citrus after a 72-h acquisition access period on infected citrus plants followed by a 21-day latent period on S. rhombifolia plants. By using the qPCR method developed for this phytoplasma, a very low pathogen titer was found both in S. marginelineatus and in infected citrus plants, which may explain, at least partially, the low transmission efficiency by this vector using citrus as a source plant. It also suggests that existence of alternative hosts that might be more adequate as inoculum sources for phytoplasma acquisition and spread by S. marginelineatus or another vector yet to be discovered.

Speciation is the process by which life diversifies into discrete forms, and understanding its underlying mechanisms remains a primary focus for biologists. Increasingly, empirical studies are helping explain the role of ecology in generating biodiversity. Adaptive radiations are often propelled by selective fitness tradeoffs experienced by individuals that invade new habitats, resulting in reproductive isolation from ancestral conspecifics and potentially cladogenesis. Host specialist insects are among the most speciose organisms known and serve as highly useful models for studying adaptive radiations. We are just beginning to understand the pace and degree with which these insects diversify. The apple maggot, Rhagoletis pomonella, is a well-studied insect whose eastern and southern populations are models for ecological speciation. Recently (40–65 ya), the fly has invaded the Pacific Northwestern United States through human-transported apples infested with larvae. There, populations of R. pomonella have rapidly colonized two novel hawthorn hosts whose fruiting times bracket apple’s (early-season native Crataegus douglasii and introduced C. monogyna, which fruits late in the season). The recent introduction might initiate host shifts, providing opportunities to examine the pace and mechanistic means with which host races (an evolutionary stage preceding speciation) become established. Here, I demonstrate that host-associated populations at a site in southwest Washington are partially allochronically isolated from one another, and life cycles temporally match with natal host fruit ripening times in sympatry. If spatially widespread, these temporal barriers could result in reproductive isolation and possibly cladogenesis. Implications of these findings reach beyond academic import, as R. pomonella is expanding not only its host range, but its geographic range is encroaching upon central Washington, the site of a multi-billion dollar per year apple-growing industry.

Solanum mauritianum (bugweed, woolly nightshade) is a perennial tree native to South America that has invaded many countries including South Africa and New Zealand. In South Africa, after 143 years of naturalization, the plant is ranked as the country‟s sixth worst weed and has invaded 1.76 million ha. Invaded areas include agricultural lands, forest plantations, water courses and conservation areas, especially in the eastern higher rainfall regions. The success of the spread of this weed is due to its production of very high numbers of bird-dispersed seeds. Since conventional control methods are unsustainable in the long term, the weed has been targeted for classical biological control since 1984. Following exploration work in its native range, biological control experts recommended that agents that are able to limit the weed‟s reproductive potential would help to manage the spread and invasiveness of this weed. Anthonomous santacruzi, a flower-feeding weevil found throughout the native range of the weed, was imported and tested between 1998 and 2002. Following approval for its release in South Africa in 2007, a new colony was imported and propagated at the University of KwaZulu-Natal Pietermaritzburg. This study was initiated to investigate aspects that could influence the release and establishment of this agent. Three aspects were investigated namely: (1) reassessing the weevil's host range to confirm that the new colony is not different from the colony tested originally and to assess the risks associated with the release of the weevil in New Zealand; (2) surveying the arthropods associated with S. mauritianum in the field to identify groups of predators that could interfere with the establishment of the weevils as well as to investigate, through laboratory-based trials using spiders as surrogate, the impact of these predators on the survival and proliferation of the weevils; and (3) propagation and release of the weevil and monitoring of its establishment. Host-specificity tests revealed that the host range of new colony is not different from that of the originally tested culture. In no-choice trials, the weevils fed and reproduced on some non-target Solanaceae species but reverted back to S. mauritianum in the choice tests. Although the risks for releasing the weevils in New Zealand were calculated to be very low, additional evidence is needed to demonstrate this conclusively. Future research to provide this evidence includes open-field trials complemented with a chemical ecology study, to resolve the case of two species, a New Zealand native and South African native, which have shown higher risks in comparison to the other tested species. For arthropods associated with S. mauritianum in the field, Araneae (especially Thomisidae), Thysanoptera, Hemiptera (especially Miridae) and Hymenoptera (especially Formicidae) were identified as generalist predators that could interfere with the establishment of A. santacruzi. However, their numbers in the field appear to be too low to provide a major threat. Also, laboratory trials using spiders as a surrogate suggested that A. santacruzi populations can survive and reproduce in the presence of such predators. The weevils were released at four sites in KwaZulu-Natal and monitoring of three of these has confirmed establishment at the warmest site along the South Coast but not at the coldest site in the Midlands. Further releases in the province are intended to complement these promising results, while additional studies are intended to facilitate the weevil's release in New Zealand. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

O Huanglongbing (HLB) é uma das mais temidas doenças da citricultura mundial, associada a bactérias do gênero Candidatus Liberibacter, que foram detectadas no Brasil em 2004. Em 2008, detectou-se outra bactéria associada a sintomas de HLB no Estado de São Paulo, que foi caracterizada como sendo um fitoplasma do grupo 16 SrIX. Fitoplasmas são molicutes fitopatógenos restritos ao floema de plantas, disseminados por insetos vetores. O presente trabalho buscou identificar cigarrinhas potencialmente vetoras do fitoplasma associado ao HLB e plantas hospedeiras desses insetos, bem como desenvolver uma técnica de quantificação de DNA desse patógeno em insetos e plantas. Amostragens de cigarrinhas foram realizadas quinzenalmente por 12 meses em dois pomares de laranja com histórico de ocorrência do fitoplasma 16SrIX na região norte do Estado de São Paulo, usando-se armadilhas adesivas amarelas em duas alturas (0,3 e 1,5 m) da copa de árvores cítricas, e rede de varredura na vegetação espontânea. Dados faunísticos identificaram uma espécie de Agalliinae (Agallia albidula Uhler) e três de Deltocephalinae, [Balclutha hebe (Kirkaldy), Planicephalus flavicosta (Stål) e Scaphytopius (Convelinus) marginelineatus (Stål)], como os cicadelídeos (Hemiptera: Cicadellidae) mais abundantes e frequentes nas áreas estudadas. Essas espécies predominaram na amostragem com rede de varredura e na menor altura de coleta com armadilhas adesivas, indicando comportamento de alimentação em vegetação rasteira. Com observações visuais, verificou-se associação das espécies com certas plantas invasoras, e influência da composição florística da vegetação rasteira sobre a abundância das cigarrinhas. S. marginelineatus e P. flavicosta ocorreram com maior frequência em Sida rhombifolia L. e Althernantera tenella Colla, respectivamente, enquanto que A. albidula foi predominante em Conyza bonariensis (L.) Cronq., e B. hebe ocorreu exclusivamente em gramíneas, principalmente Panicum maximum Jacq.. Plantas invasoras amostradas nas áreas foram testadas para a presença do fitoplasma 16SrIX, porém sem resultados positivos. No entanto, amostras de campo da cigarrinha S. marginelineatus foram positivas por PCR e sequenciamento para o referido fitoplasma. Indivíduos de S. marginelineatus criados em laboratório e mantidos por um período de acesso à aquisição de 72 h em citros infectado com o fitoplasma 16SrIX, foram capazes de transmití-lo para citros, após 21 dias de latência, porém com baixa eficiência (0,5%). Por meio de PCR quantitativo desenvolvido para esse fitoplasma, verificou-se baixo título do patógeno tanto em S. marginelineatus, quanto em plantas cítricas infectadas, o que pode explicar, pelo menos em parte, a baixa eficiência de transmissão pelo inseto tendo citros como fonte. Isto sugere a existência de outros hospedeiros mais adequados como fontes de inóculo para aquisição do fitoplasma por S. marginelineatus ou outro vetor ainda desconhecido. / Huanglongbing (HLB) is a severe citrus disease associated to phloemlimited bacteria in the genus Candidatus Liberibacter, which were detected in Brazil in 2004. In 2008, another bacterium was found in association with HLB symptom in the São Paulo State, and characterized as a phytoplasma belonging to 16SrIX group. Phytoplasmas are vector-borne phytopathogenic mollicutes that inhabit plant sieve elements. The goals of this study were to identify potential leafhopper vectors of the HLB-associated phytoplasma and their host plants, as well as to establish a real-time PCR procedure for pathogen quantification in vectors and plants. Leafhoppers were sampled fortnightly for 12 months by yellow sticky cards placed at two heights (0.3 and 1.5 m) on the citrus tree canopy and by sweep net in the ground vegetation of two sweet orange groves with history of infection by the 16SrIX phytoplasma, in the northern region of São Paulo State. Faunistic analyses indicated 1 Agalliinae (Agallia albidula Uhler) and 3 Deltocephalinae [Balclutha hebe (Kirkaldy), Planicephalus flavicosta (Stål) e Scaphytopius (Convelinus) marginelineatus (Stål)] species that were the most abundant and frequent leafhoppers (Hemiptera: Cicadellidae) in the experimental areas. These species predominated in sweep net and in sticky traps catches at 0.3 m above soil, showing that they inhabit the ground vegetation. Visual observations indicated a strong association of leafhopper species with some weeds and the influence of weed species composition on leafhopper abundance in the ground vegetation. S. marginelineatus and P. flavicosta were more frequent on Sida rhombifolia L. and Althernantera tenella Colla, respectively, while A. albidula was observed more often on Conyza bonariensis (L.) Cronq., and B. hebe occurred solely on grasses, more abundantly on Panicum maximum Jacq. Fourteen weed species sampled in the area were PCR tested for infection by the 16SrIX phytoplasma, but none was found infected. Nevertheless, 3 out of 30 field-collected samples (10 adults per sample) of S. marginelineatus tested positive for this phytoplasma by PCR and sequencing. Healthy lab-reared adults of S. marginelineatus were able to transmit inefficiently (0,5%) the 16SrIX phytoplasma to healthy citrus after a 72-h acquisition access period on infected citrus plants followed by a 21-day latent period on S. rhombifolia plants. By using the qPCR method developed for this phytoplasma, a very low pathogen titer was found both in S. marginelineatus and in infected citrus plants, which may explain, at least partially, the low transmission efficiency by this vector using citrus as a source plant. It also suggests that existence of alternative hosts that might be more adequate as inoculum sources for phytoplasma acquisition and spread by S. marginelineatus or another vector yet to be discovered.

Os enfezamentos vermelho e pálido são importantes doenças do milho, causadas, respectivamente, por um fitoplasma e por um espiroplasma (Spiroplasma kunkelii). As duas formas de enfezamento foram relatadas no Brasil no início da década de 70 e se tornaram economicamente relevantes no início dos anos 80, com a introdução de novas técnicas de cultivo no milho. Apesar de ser um patossistema conhecido e estudado, ainda há certos pontos em relação à doença que permanecem desconhecidos. Um deles é em relação à sobrevivência do vetor (Dalbulus maidis) e do patógeno durante a entressafra. Outro, diz respeito às alterações bioquímicas envolvidas na relação hospedeiro-patógeno. O presente trabalho visou avaliar algumas gramíneas, usadas na formação de pastagens, e ervas-daninhas, que ocorrem nas áreas cultivadas com milho, como possíveis hospedeiros alternativos destes patógenos; ainda, buscouse estudar algumas alterações bioquímicas que ocorrem nas plantas de milho quando infectadas por espiroplasma. Para isto, o trabalho foi desenvolvido em três etapas. Na primeira, onze espécies de capins e ervas daninhas foram experimentalmente inoculadas com o espiroplasma através do vetor. As avaliações foram realizadas com base na observação de sintomas, na detecção molecular do espiroplasma nos tecidos das plantas inoculadas e na contagem de insetos sobreviventes nestas plantas inoculadas. Como resultado, nenhuma das espécies testadas mostrou resultado positivo para presença do patógeno inoculado e não demonstrou capacidade em hospedar o espiroplasma. Em uma segunda etapa, três gramíneas sabidamente infectadas com o fitoplasma do enfezamento vermelho do milho (capim colonião, capim braquiária e capim marmelada) foram testadas quanto à capacidade de servirem como planta-fonte na aquisição do fitoplasma pelo vetor. Após o estabelecimento dos insetos nestas plantas, os mesmos foram transferidos para plantas sadias de milho. As avaliações também foram realizadas com base na observação de sintomas e detecção molecular do fitoplasma nos tecidos das plantas inoculadas. Das três espécies testadas como hospedeiras alternativas, o capim colonião demonstrou ser um hospedeiro alternativo do fitoplasma. Estes resultados trouxeram uma significativa contribuição ao melhor conhecimento da epidemiologia da doença, mostrando a existência de outro hospedeiro do patógeno além do milho. Na última etapa, foram escolhidos um híbrido suscetível e um resistente, os quais foram inoculados com cigarrinhas infectadas pelo espiroplasma e submetidos à análise bioquímica para avaliação de alguns compostos, como proteínas, fenóis, clorofilas, açúcares e as enzimas peroxidase e -1,3-glucanase. Amostras foliares foram coletadas e avaliadas em 6 diferentes períodos: 0, 10, 20, 40, 60 e 80 dias após a inoculação. Os resultados revelaram um aumento na quantidade de todos os compostos avaliados, porém uma redução na clorofila e proteína total para o híbrido suscetível. As análises evidenciaram que as alterações nas atividades enzimáticas parecem fazer parte de uma resposta inespecífica de defesa da planta. / The maize bushy stunt and corn stunt are relevant diseases caused, respectively, by a phytoplasma and a spiroplasma (Spiroplasma kunkelii). Both kinds of stunting were reported in Brazil in the beginning of the 1970´s and became economically important in the beginning of the 1980´s, with the adoption of new techniques for maize cultivation. Although this pathosystem has been well studied, there are still some unknown points related to the diseases. One of them is related to survival of the leafhopper vector (Dalbulus maidis) and pathogens during the maize off-season. The other one is related to biochemical changes involved in the host-pathogen interaction. This research aimed to evaluate some pasture grasses and weeds that occur on areas cultivated with corn as possible alternatives hosts for these pathogens; an additional study was conducted to investigate biochemical alterations in maize plants infected by S. kunkelii. So, the research was carried out on three steps. First, eleven species of grasses and weeds were inoculated with S. kunkelii by using infective leafhoppers. The evaluations were based on symptoms and molecular detection of the pathogen in the inoculated plants, as well as on counting of surviving insects onto these inoculated plants. S. kunkelii was not detected by PCR or symptoms in any of the inoculated plant species, indicating that they are not able to host this pathogen. In the second step, three species of grasses (Panicum maximum, Brachiaria plantaginea and Brachiaria decumbens) infected with the maize bushy stunt phytoplasma (MBSP) were tested as source plants of this pathogen for acquisition by its vector. After insects establishing on these plants, they were transferred to healthy corn plants. Transmission to maize was determined based on symptoms and molecular detection of the phytoplasma in the inoculated plant tissues. Out of the three grass species tested, only P. maximum was shown to serve as an alternative host of the phytoplasma. These results represent a relevant contribution to understanding of the disease epidemiology, indicating a species distinct of maize as a source plant for MBSP. In the last study, a susceptible and a resistant hybrid were inoculated with S. kunkelii by infective leafhoppers. Biochemical analyses were carried out to evaluate changes in proteins, phenols, chlorophylls, total sugars and enzymes peroxidase and -1, 3 glucanase. Leaf samples were harvested at 6 different times: 0, 10, 20, 40, 60 and 80 days after inoculation. Results revealed an increase in all biochemical parameters evaluated, with exception for the chlorophyll content and soluble protein in a susceptible hybrid that decreased. The analysis showed that enzyme activity may be an unspecific response of the plant to the pathogen.

Os nematoides que atualmente tem sido classificados como P. coffeae, demonstram ampla variabilidade morfológica, molecular e quanto à reação à diferentes hospedeiros. Por conseguinte, é essencial que se identifique corretamente as espécies e que se conheça a capacidade de parasitismo em alguns hospedeiros, para que se possa estabelecer medidas de controle e estimar eventuais riscos da entrada de um patógeno em uma área com hospedeiro suscetível. Neste sentido, a presente pesquisa propõe, numa primeira parte, uma medida de controle de P. jaehni (K5), que é muito agressivo à cafeeiro arábico, baseada no uso de plantas má hospedeiras. Na segunda parte deste trabalho é realizada uma caracterização da reação de diferentes espécies vegetais à quatro populações de Pratylenchus spp. Em virtude do exposto, este estudo objetivou avaliar a reação de diferentes cultivares de feijoeiro comum frente à P. jaehni (K5), visando seu possível uso no manejo de áreas cafeeiras infestadas e caracterizar a reação de diferentes espécies vegetais de importância econômica (café, porta-enxertos cítricos, banana e sorgo) frente à quatro populações de Pratylenchus spp. As populações inciais utilizadas nos experimentos variaram entre 180 e 200 nematóides. Em todos os experimentos, os nematóides foram extraídos das raízes pelo método de Coolen e D´Herde (1972) e, eventualmente, do substrato pelo método de Jenkins (1964). Foram realizados três ensaios: i) o primeiro com feijoeiro comum, onde todas as cultivares utilizadas foram resistentes à P. jaehni (K5), inclusive na réplica; ii) o segundo com porta-enxertos cítricos, no qual somente o limão-cravo foi hospedeiro de P. jaehni (K5); iii) o terceiro, no qual foi utilizado café, limão-cravo, banana e sorgo para o conhecimento das respectivas reações frente à 4 populações de Pratylenchus spp. Neste último experimento ocorreu uma reação hospedeira diferenciada para cada população. De acordo com os resultados, concluise que as cultivares de feijoeiro comum utilizadas apresentam potencial de uso em áreas cafeeiras infestadas por P. jaehni (K5), em consórcio ou em áreas de renovação de cafezal, e que as populações de Pratylenchus spp. são capazes de se reproduzir de forma diferenciada frente às espécies vegetais testadas. / Nematode populations that have been classified as P. coffeae show wide morphological, molecular and host range variability. Therefore, is essential the correct identification of the species and the knowledge about its parasitism capacity on some hosts, to ensure appropriate control measures and to estimate the entry risks of a pathogen in an area with susceptible host. In this sense, the present research report, firstly, propose a control measure of P. jaehni (K5), which is very aggressive to the arabic coffee, based on the use of poor host plants. In the second part, was carried out a host status evaluation of different plant species to four populations of Pratylenchus spp. In this context, were evaluated the reaction of different common bean cultivars to P. jaehni (K5), for its possible use in management of coffee areas infested with this nematode, and characterized the response of different economic important plant species (coffee, citrus rootstocks, banana and sorghum) to four populations of Pratylenchus spp (IB01P, IB02P, K5 e C1). The initial population used in experiments ranged between 180 and 200 nematodes. In all experiments, nematodes were extracted from roots by Coolen e D\'Herde´s method (1972) and eventually from the substrate by Jenkins´ method (1964). Three assays were conducted and results was as following: i) in the first one, with common bean, all tested cultivars were resistant to P. jaehni (K5), including the replica; ii) in the second one, with rootstocks, only rangpur lime was a good host of P. jaehni (K5); iii) in the third one, in which was used coffee, rangpur lime, banana and grain sorghum, was observed a differential host reaction for each nematode population evaluated. According to the present results, we suggest that common bean cultivars tested have great potential for use, or in intercropping or in crop rotation, in coffee areas infested by P. jaehni (K5) and populations of Pratylenchus spp. have different reproductive fitness in the plants species tested.

This study lists and compares insect herbivores of Senecio inaequidens and of Senecio pterophorus around Butterworth by 18 Tables and 38 Figures. The two plant species are widely distributed around Southern Africa. Samples were taken during a month of each of the four main seasons of the year, which in Butterworth did not show much difference in temperature. The two plant species shared generalist insect herbivores most of which were also on other surrounding plant species. The population of most of the herbivores was affected by the seasons while the two plant species were not seasonal, thus the correlation between insect herbivores and the two plant species was not significant. The heavier, and apparently chemically protected species, Senecio pterophorus, accommodated borers and supported a wider variety of but fewer individual insects. Senecio pterophorus could be having more defences but had more serious herbivores. There were no serious insect herbivores that could control the abundance of the two plant species around Butterworth. Anatomical differences between S. pterophorus and S. inaequidens could be highlighted by the kind and number of insect herbivores found upon them. Similarities were more difficult to identify through studying their insect herbivores. The biology of one serious weed, Lixus sp., on Senecio pterophorus was studied in more detail. The life cycle of the weevil was found to be synchronised with that of the host. This weevil shared the stems with other species of weevils with no indication of competition.

Aphthona spp. flea beetles were released in the Little Missouri National Grasslands (LMNG) in western North Dakota in 1999 to control leafy spurge (Euphorbia esula L.). The changes in soil seed bank composition and leafy spurge density were evaluated on two ecological sites five (2004) and ten years (2009) after Aphthona spp. release to monitor the effectiveness of the insects on weed control and associated change in plant communities. In 2009, leafy spurge stem density averaged 2 and 9 stems m-2 in the loamy overflow and loamy sites, respectively, compared to 110 and 78 stems m-2, respectively, in 1999 and 7 and 10 stems m-2, respectively, in 2004. Leafy spurge constituted nearly 67% of the loamy overflow seed bank in 1999 compared to 17% in 2004 and 2% in 2009. In the loamy seedbank, the weed represented nearly 70% in 1999 compared to approximately 11% in 2004 and 15% in 2009. As leafy spurge was reduced, native species diversity and seed count increased ten years following Aphthona spp. release. High-seral species represented 17% of the loamy overflow seedbank in 2009, an increase from 5% in 1999. However, Kentucky bluegrass, a non-target weedy species, increased over 250% in the loamy overflow seedbank from 2004 to 2009. The reestablishment of native plant species has often been slow in areas where leafy spurge was controlled using Aphthona spp. A bioassay was completed to evaluate native grass establishment when grown in soil from Aphthona spp. release and non-release sites throughout North Dakota. Native grass production was not affected when grown in soil collected from established Aphthona spp. sites (1.5 g per pot) compared to soil without insects (1.6 g per pot). The cause of reduced native grass production in sites with Aphthono spp. previously observed is unknown but may have been due to a chemical inhibition caused by the insects within the soil that no longer exists. The native warm-season switchgrass (Ponicum virgotum L.) may be an alternative to corn for efficient biofuel production; however, control of cool-season grassy weeds has been a problem in switchgrass production. Various herbicides were evaluated for smooth bromegrass (Bromus inermis Leyss.) and quackgrass [Elymus repens (L.) Gould] control in an established switchgrass stand near Streeter, ND and a weed-infested field in Fargo, ND. Switchgrass yield was higher than the control 14 mo after treatment (MAT) when aminocyclopyrachlor or sulfometuron were applied early in the growing season, but no treatment provided satisfactory long-term grassy weed control. Herbicides were reevaluated at increased rates for smooth bromegrass or quackgrass control in Fargo. Sulfometuron provided 99% smooth bromegrass control when applied at 280 g ha-1 in the fall but injured other grass and forb species as well. Sulfometuron would likely be injurious to switchgrass and could not be used for biofuel production. Aminocyclopyrachlor did not injure other grass species but only reduced smooth bromegrass control by 76% when applied at 280 g ha-1 in the fall. No treatment provided satisfactory long-term quackgrass control.

The Russian wheat aphid (RWA) (Diuraphis noxia Kurdjumov) is one of the important insect pests of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and other grasses. To date, there are four RWA biotypes identified in South Africa. The virulent biotypes emerged, partly due to climate change and new genetic variations within populations of RWA; hence there is a need to improve host-plant resistance, as an effective control measure. Bread wheat (Triticum aestivum L.) accession Cereal Introduction (CItr) 2401 is known to be resistant to all RWA biotypes worldwide. The goal of this study was to use a backcrossed near-isogenic line (NIL) BC5F5 mapping population, developed from a cross between CItr 2401 and susceptible Kavkaz, to identify and validate single nucleotide polymorphism (SNP) markers linked to the resistance phenotype in CItr 2401. This was achieved by (i) conducting a preliminary study that evaluated the suitability of simple sequence repeat (SSR) markers previously reported in literature for discriminating stacked RWA resistance genes and, (ii) employing SNP markers for the first time in a RWA resistance study as a future alternative to the widely used SSR markers. None of the tested SSR markers showed potential use in marker-assisted selection (MAS). The mapping population was phenotypically evaluated for RWA resistance using the four South African biotypes, viz. RWASA1, RWASA2, RWASA3 and RWASA4. Analysis of variance (ANOVA) showed significant (P<0.001) differences of genotypes after confirming the normality of residuals and homogeneity of variance. The Illumina iSelect 9,000 wheat SNP platform was used to genotype the two crossing parents and a selection of 24 NIL genotypes from the mapping population. Eight SNP markers found to be linked to the phenotype were converted to breeder-friendly and high-throughput Kompetitive allele-specific polymerase chain reaction (KASP) markers. The designed KASP markers were validated on the two crossing parents, the 24 NIL sent for SNP genotyping, on the mapping population and on the preliminary study genotypes for their effectiveness. The KASP assays developed in this study will be useful for stacking the RWA resistance from CItr 2401 with other Dn genes effective against the RWA. / Life and Consumer Sciences / M. Sc. (Life Sciences)

Predatory Ground beetles (Coleoptera: Carabidae) and Lady beetles (Coleoptera: Coccinellidae) are two of the most diverse groups found in wheat agroecosystems, globally. These groups are important from both an economic and ecological perspective due to their natural services provision. The effect of wheat agroecosystem management on species diversity, abundance, biomass and composition in South Africa is not yet documented, and there is no existing data indicating which predatory carabid and coccinellid species provides essential ecosystem services and bioindicator roles. Therefore, we examined the effects of organic, conventional and intercropped agroecosystems on ground beetle and lady beetle abundance, dried weight (biomass), composition and diversity. Sampling of wheat agroecosystems was conducted in three systems i.e. organic, conventional and organic intercropped. Post-hoc Tukey test indicated a statistically significant difference between species diversity, biomass and abundance in organic and intercropped systems compared to the conventional systems. Regression analysis indicated significant positive correlation between aphid’s density and predatory carabid and coccinellid beetles in the intercropped systems. Amongst the weather factors temperature influenced aphid density and carabid and coccinellid beetles’ abundance. PCA (Principal Component Analysis) revealed significant positive correlation between individual biomass and cropping system. Conventional system showed a negative correlations with carabid and coccinellid individual biomass. We found that some carabid and coccinellid species can be used to measure the quality of agroecosystems. This study provides a fundamental basis for identification and monitoring of carabid and coccinellid species and their role as bioindicators of ecological disturbance. The identified bioindicator species in this study can assist in developing conservation and biomonitoring strategies within agroecosystems. / Agriculture and  Animal Health / M. Sc. (Agriculture)