Submitted by FERNANDA DA SILVA VON PORSTER (fdsvporster@univates.br) on 2016-07-27T17:50:14Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) 2016MaiconToldi.pdf: 1223571 bytes, checksum: 8d5afc2a1dc5fe44e12a9a7cf2ee7291 (MD5) / Approved for entry into archive by Ana Paula Lisboa Monteiro (monteiro@univates.br) on 2016-08-30T11:47:26Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) 2016MaiconToldi.pdf: 1223571 bytes, checksum: 8d5afc2a1dc5fe44e12a9a7cf2ee7291 (MD5) / Made available in DSpace on 2016-08-30T11:47:26Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) 2016MaiconToldi.pdf: 1223571 bytes, checksum: 8d5afc2a1dc5fe44e12a9a7cf2ee7291 (MD5) Previous issue date: 2016-07 / CAPES / As cultivares geneticamente modificadas alteram o manejo da cultura da soja (Glycine max L. Merril: Fabaceae). O aumento no uso de agroquímicos decorrentes do plantio de transgênicos é exemplo de prática que coloca em cheque o futuro dos solos e biodiversidade. Dentre as espécies de ácaros fitófagos que causam danos à cultura destacam-se Mononychellus planki McGregor e Tetranychus ludeni Zacher. O Caliothrips phaseoli Hood (Thysanoptera: Thripidae) também pode atingir nível de praga nestas plantações. Estes ácaros e inseto se alimentam das folhas da soja causando clorose e perda na produção de grãos. Neoseiulus californicus McGregor (Acari: Phytoseiidae) é utilizado no controle de populações de ácaros praga em culturas agrícolas, porém não são conhecidos seus parâmetros biológicos quando alimentados com M. planki e C. phaseoli. O objetivo deste trabalho foi conhecer os parâmetros biológicos de N. californicus quando alimentado de M. planki, T. ludeni e C. phaseoli sobre folhas de soja nas condições de laboratório e avaliar a influência da transgenia sobre o ciclo biológico de T. ludeni. Os ácaros foram coletados em plantações de soja da cidade de Lajeado - RS. No estudo com o predador foram utilizados ovos individualizados em arenas com M. planki, T. ludeni e C. phaseoli como alimento. Foram realizados estudos observando o desenvolvimento e reprodução de T. ludeni sobre soja convencional Fundacef 44, RR Nideira 5909, resistente ao glifosato e BT Rota 54, resistente ao glifosato e ao ataque de lagartas. A viabilidade total de ovo-adulto para o predador se alimentando de T. ludeni, M. planki e C. phaseoli foram 96.66%, 76.67% e 53.33%, respectivamente. O predador não completou seu desenvolvimento sendo alimentado com C. phaseoli, pois não houve oviposição. A capacidade de aumentar em número (rm) foi de 14.46 fêmeas/fêmeas/dias com T. ludeni e 13.39 com M. Planki. A transgenia na soja não demonstrou interferir na biologia de T. ludeni. Esta espécie pode estar em fase de adaptação à cultura, pois teve parâmetros de reprodução menores que o esperado. Os resultados poderão subsidiar trabalhos de controle biológico na soja e outras culturas que apresentarem as mesmas espécies herbívoras em nível de praga. Também contribuir para as discussões acerca do uso de transgênicos. / The genetically modified cultivars change management culture of soybean, Glycine max L. Merri: Fabaceae. The dramatic increase in the use of agrochemicals arising from the planting of GM crops is practical example that puts in check the future of soil and agricultural biodiversity. Among the species of phytophagous mites that cause damage to culture, include Mononychellus planki McGregor, Tetranychus ludeni Zacher and Tetranychus urticae Koch. Caliothrips phaseoli Hood (Thysanoptera: Thripidae) is a species of insect that can also reach plague level in these plantations. The species lay their eggs on the leaves of soybeans and feed her causing chlorosis and loss in grain production. Neoseiulus californicus McGregor is already used in the control of pest mites in different cultures, but are not known their biological parameters feeding on M. planki and C. phaseoli. The aim of this study was to evaluate the biological parameters of N. californicus feeding on M. planki, T. ludeni and C. phaseoli in soybean leaves and the influence of transgenic on an herbivore, T. ludeni. The mites were collected in soy plantations in the city of Lajeado-RS. In the study with the predator, individualized eggs were used in arenas with M. planki, T. ludeni and C. phaseoli as food. Noted the development and reproduction of t. ludeni in different soybean cultivars, these being, conventional soybeans Fundacef 44, and of two types of genetically modified soybeans, RR Nideira 5909 glyphosate resistance e BT Rota 54 glyphosate resistant and the attack of caterpillar. The total egg viability-adult for the predator feeding on T. ludeni, M. planki and C. phaseoli was 96.66% respectively, 76.67% and 53.33%. The predator has not completed its development being fed with C. phaseoli, do you ovipositou. The ability to increase in number (rm) was 14.46 with T. ludeni and 13.39 female/female/day with M. planki. The varieties in soybeans has not shown to interfere with the biology of T. ludeni. Is species may be in the process of adaptation to the culture, as it had playback parameters smaller than expected. The results may subsidize works of biological control in soybeans and other crops which submit same herbivore species pest level. Also, contribute to discussions about the use of transgenic crops.

京都大学 / 新制・課程博士 / 博士(農学) / 甲第23618号 / 農博第2481号 / 新制||農||1088(附属図書館) / 学位論文||R4||N5366(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 日本 典秀, 教授 田中 千尋, 准教授 刑部 正博 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第20422号 / 農博第2207号 / 新制||農||1047(附属図書館) / 学位論文||H29||N5043(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 天野 洋, 教授 田中 千尋, 准教授 刑部 正博 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Made available in DSpace on 2016-12-23T14:37:41Z (GMT). No. of bitstreams: 1 Victor Bernardo Vicentini.pdf: 513256 bytes, checksum: bf76720c0875136373cb9c67a26379d6 (MD5) Previous issue date: 2010-02-19 / O ácaro rajado Tetranychus urticae Koch (1836) (Acari: Tetranychidae) é uma praga que causa dano ao morangueiro, atacando as folhas e acarretando grandes prejuízos. Portanto, este trabalho avalia os efeitos dos extratos de plantas e indutores de resistência sobre o ácaro rajado no morangueiro. No experimento com extratos botânicos, concentrações de extratos de folhas de Cymbopogon winterianus (citronela), extratos de frutos de Sapindus saponaria (saboneteira), formulado de nim (Azamax®) e Emulsionável Pratissoli (0, 1, 2, 3, 4, 5%) foram aplicadas sobre discos de folhas de morangueiro da cultivar Camarosa, acondicionadas em placa de Petri e infestadas com 10 fêmeas de T. urticae, sendo utilizadas 10 repetições por concentração. Na testemunha, foi utilizada água destilada. As avaliações foram realizadas 24, 72 e 120 horas após o início do experimento, observando-se a mortalidade e o número de ovos do ácaro rajado. A partir dos dados obtidos, foram estimadas as CL50. O experimento foi mantido em câmara climatizada, a temperatura de 25 ± 1 ºC, 70 ± 10% de UR e fotofase de 12 h. O formulado Azamax®, o emulsionável Pratissoli e todos os extratos vegetais causaram mortalidade em fêmeas do ácaro rajado, além de interferir na oviposição. Destacaram-se o extrato de saboneteira e o emulsionável Pratissoli por obterem menores CL50, portanto, são mais tóxicos. Dessa forma, a utilização dos extratos vegetais e do emulsionável Pratissoli pode ser uma alternativa com potencial de manejo para o ácaro rajado. Em relação aos indutores de resistência, avaliou-se o efeito da indução de resistência em morangueiro em relação ao ácaro rajado, utilizando argila silicatada, silicato de potássio e metassilicato de sódio em concentrações de 1%, avaliando-se a mortalidade de fêmeas adultas de T. urticae e o número de ovos. As avaliações foram realizadas após a 1°, 2° e 3° aplicações foliares dos produtos em plantas de morangueiro cultivar Camarosa. Na testemunha, foi aplicado água destilada. Após as aplicações, discos de folhas foram retiradas das plantas e acondicionadas em placas de Petri, logo, foram infestadas com 10 fêmeas de ácaro rajado em um total de 10 discos de folhas e, finalmente, mantidas em câmara climatizada a temperatura de 25 ± 1 ºC, 70 ± 10% de UR e fotofase de 12 h. Após 120 horas, a mortalidade foi quantificada e posteriormente corrigida pela fórmula de Abbott (1925), sendo também observado o número de ovos. Os tratamentos submetidos à argila silicatada e silicato de potássio apresentaram maior mortalidade quando comparados à testemunha, obtendo, resultados significativamente melhores com 3 aplicações. A redução do número de ovos foi significativa para todos os tratamentos quando comparados à testemunha na terceira aplicação, ressaltando o tratamento com silicato de potássio que conferiu maior redução. Esses resultados demonstram que a indução de resistência é uma medida com potencial para o manejo dessa praga em cultivos de morangueiro / Two-spotted spider mite Tetranychus urticae Koch (1836) (Acari: Tetranychidae) is a pest that causes damage to the strawberry, attacking the leaves and causing extensive damage. Therefore, the objective of this study was to evaluate the effects of plant extracts and inducers of resistance on the mite in strawberry. In the experiment with botanical extracts, concentrations of leaf extracts of Cymbopogon winterianus (citronella), extracts of Sapindus saponaria (saboneteira), formulated neem (Azamax ®) and Emulsionável Pratissoli (0, 1, 2, 3, 4, 5%) were applied to discs leaves of the strawberry variety Camarosa placed in a Petri dish and infested with 10 females of T. urticae, using 10 replicates per concentration. In witness it was used distilled water. Evaluations were performed 24, 72 and 120 hours after the start of the experiment, observing the mortality and the number of spider mite eggs. LC50 was estimated from data obtained. The experiment was kept at temperature of 25 ± 1º C, 70 ± 10% RH and photophase of 12 h. The formulated Azamax ®, emulsionável Pratissoli and all plant extracts caused mortality on female spider mite, and interfere with the oviposition. The extract of S. saponaria and emulsionável Pratissoli were the most notorious for having lower LC50,thus are more toxic. Thus, the plant extracts and emulsionável Pratissoli can be an alternative with potential for management mite. In the test with inductons of resistance, it was evaluated the effect of induction in strawberry against the spider mite, calcium silicate, potassium silicate and sodium metasilicate applications at concentrations of 1%, assessing the mortality of adult females of T. urticae and the number of eggs. The evaluations were performed after 1, 2 and 3 foliar applications of products on Camarosa strawberry plants cultivar. Test control was applied distilled water. Forward the applications, leaf discs from plants was placed in Petri dishes, then, were infested with 10 female mite in a total of 10 leaf discs, and kept at temperature of 25 ± 1 º C, 70 ± 10% RH and photophase of 12 h. After 120 hours the mortality was quantified and subsequently corrected by Abbotts formula (1925), and also observed the number of eggs. Tests underwent silicate clay and potassium silicate showed higher mortality compared to the control, obtaining significantly better results with 3 applications. Reducing the number of eggs was significant for all tests when compared to the control at the third application, with emphasis on test with potassium silicate assigning higher reduction. These results show that the induction of resistance is a potential method for this pest in strawberry crops

The spider mite family (Tetranychidae) is a well known pest group in agriculture. Within this family, Willamette spider mite (Eotetranychus willamettei) causes physical harm and potential damage to grapevines (Vitis vinifera) along the central and north coast of California as well as Washington and Oregon. Willamette spider mite prefers cooler climates and feeds by puncturing the plant leaf tissue; therefore removing plant nutrients in the early stages of plant growth. Amending soils with fertilizer is a common cultural practice used in commercial vineyards, but no study has documented the interaction between the effects fertilizer concentrations have on Willamette spider mite. This project consisted of a field study (at Cambria Vineyards & Winery, Santa Maria, CA) and a laboratory study (at a California Polytechnic State University, San Luis Obispo campus greenhouse). The field study tested the effects potassium, nitrogen, and control (unfertilized) treatments had on Willamette spider mite on ‘Chardonnay’ grapes. Field results showed no significant difference among the three treatments, but suggest a response, given that mite density peaked highest in the potassium treatment and had a second high peak in the nitrogen treatment. In addition, egg density peaked highest in the potassium treatment. The lab study tested the effect four different nitrogen treatments had on Willamette spider mites. Treatments ranged from High N (1500 ppm N fertilizer), Med-High N (1500 ppm N fertilizer), Med–Low N (500 ppm N fertilizer), and Low N (0-50 ppm N fertilizer). Four parameters were tested: male and female days to maturation, male and female survivorship to adult, adult female longevity and oviposition. Longevity and oviposition lab results indicate that Willamette spider mite has a non-linear response to grape N concentration. Performance was better within the two medium treatments compared to High N and Low N treatments. Survivorship suggests the same as days to maturation although not statistically significant.

Submitted by YOANDRY RODRIGUEZ RIVERO (yoandryrodriguez52@gmail.com) on 2018-04-26T18:24:48Z No. of bitstreams: 1 Dissertação_Yoandry_Rodríguez_Rivero.pdf: 1480495 bytes, checksum: 47881570b9b09290e8f11eb531a7f0ba (MD5) / Approved for entry into archive by Alexandra Maria Donadon Lusser Segali null (alexmar@fcav.unesp.br) on 2018-05-02T19:09:07Z (GMT) No. of bitstreams: 1 rodríguezrivero_y_me_jabo.pdf: 1480495 bytes, checksum: 47881570b9b09290e8f11eb531a7f0ba (MD5) / Made available in DSpace on 2018-05-02T19:09:07Z (GMT). No. of bitstreams: 1 rodríguezrivero_y_me_jabo.pdf: 1480495 bytes, checksum: 47881570b9b09290e8f11eb531a7f0ba (MD5) Previous issue date: 2018-03-02 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / No Brasil, diversos ácaros-praga podem atacar a cultura do amendoim (Arachis hypogaea), sendo responsáveis por significativas perdas na produtividade. Na tentativa de avaliar as estratégias de controle biológico conservativo dessas pragas, foi realizado uma caracterizção do sistema de cultivo de amendoim em sucessão com cana-de-açúcar (Saccharum officinarum), cana-soca e cana-planta, em uma área comercial, e uma comparação entre dois sistemas de plantios, um consorciado com sorgo (Sorghum bicolor) e girassol (Helianthus annuus) e o outro convencional, em parcelas experimentais, ambos no município de Jaboticabal-SP, Brasil. O levantamento e coleta das espécimes de artrópodes na cultura do amendoim foi realizado por meio de observações a campo e instalação de armadilhas entomológicas. Além disso, foram avaliadas as doenças fúngicas e plantas espontâneas na cultura, por sua incidência direta na produtividade. Também se avaliaram culturas como o feijão (Phaseolus vulgaris) e a soja (Glycine max), comuns na região, assim como cercas vivas de sansão-do-campo (Mimosa caesalpiniifolia). Quanto à análise entomofaunística das áreas, os dados foram processados com o programa AnaFau e as análises de variância com STATISTICA, versão 6. O sistema consorciado apresentou menor ocorrência de artrópodes-pragas do amendoim. Embora os valores da diversidade de espécies em ambos os plantios foram próximos, o consorciado teve maior riqueza de espécies, incluindo inimigos naturais. Destes últimos, foi demostrado que Zelus illotus, nas fases estudadas, independentemente de apresentar dominância nas áreas, não preda o ácaro Tetranychus ogmophallos. Com exceção do amendoim, nenhuma planta avaliada foi hospedeira de T. ogmophallos, sendo as altas densidades de amendoim tiguera em cana planta o principal fator de estabelecimento e dispersão dos ácaros e de outras pragas para a cultura na região. Estes resultados são úteis para a melhoria contínua dos programas de renovação de canaviais com a cultura do amendoim. / In Brazil, many pest mites can attack crops of peanuts (Arachis hypogaea), being responsible for significative losses in productivity. To evaluate the strategies of conservative biological control of these pests, a characterization of the sowing system of peanuts in rotation with sugarcane (Saccharum officinarum), in ratoon cycle and plant cane, in a commercial area, and a comparative between two sowing systems, one intercropped with sorghum (Sorghum bicolor) and sunflower (Helianthus annus) and other conventional, in experimental plots, were performed in the municipality of Jaboticabal-SP, Brazil. The survey and sampling of arthropod species in the peanut crop was performed through field observations and entomologic traps in the field. Furthermore, the ocurrence fungic diseases and weeds were evaluated in the crop, due to their direct impact on productivity. Crops as bean (Phaseolus vulgaris) and soybean (Glycine max), commons in the region, as the hedge plant sansão-do-campo (Mimosa caesalpiniifolia) were also evaluated. For the faunistic analysis, the data was processed using the Software Anafau and the variance analysis using the software STATISTICA, version 6. The intercropping system presented the lower occurrence of pest arthropods in the peanut crop. Although the diversity values of diversity in both sowing system were near, the intercropping system presented higher species richness, including natural enemies. Among those, it was shown that Zelus illotus, in the stages studied, do not prey on Tetranychus ogmophallos. With the exception of peanuts, none of the other evaluated plants hosted T. ogmophallos, being the volunteer peanut in plant cane the responsible for the establishment and dispersal of mites and other peanut pests in the region. The results are important for the continuous improvement of rotation systems on sugarcane crops. / 190185/2015-5

Host-plant resistance is an important component of integrated pest management. Host resistance to phytophagous insects and mites based on chemical and morphological characteristics has been identified in various agronomic crops. The present study was undertaken to examine how variation in selected morphological and chemical characteristics of beach strawberry Fragaria chiloensis (L.) Duchesne affects population parameters of the twospotted spider mite Tetranychus urticae Koch. The results from this study show that clones of F. chiloensis and the cultivar "Totem" vary in suitability for the twospotted spider mite. Selected clones of F. chiloensis and the cultivar "Totem" differed also in the following foliar characteristics: densities of glandular and nonglandular trichomes and concentrations of total and catechol-based phenolics. In contrast, qualitative analysis of phenolic compounds, determined via HPLC, revealed a close similarity between F. chiloensis and F. x ananassa (cultivated strawberry) and among selected clones of F. chiloensis. Mite oviposition was negatively correlated with densities of glandular and nonglandular trichomes and concentrations of total foliar phenolics. In spite of these significant relationships, mite oviposition was best predicted by a combination of interacting plant characteristics rather than by any individual characteristic. Entrapment by sticky exudates from glandular trichomes appears to explain the negative relationship between mite survival and density of glandular trichomes. Spider mite development was negatively related to concentrations of foliar phenolics; twospotted spider mite development is delayed on leaves with high concentrations of phenolics. The correlation between mite development and foliar phenolics was greater when catechol-based phenolics were used. / Land and Food Systems, Faculty of / Graduate

The aims of this study were to develop a detailed record of the tetranychid mites of Kenya and Tanzania, to assess the diversity of tetranychid mites in the east African biodiversity hotspots and to determine female characters that can be used to identify the species of the economically important Tetranychus species found in these countries. The genetic diversity of the most abundant Tetranychus species (Tetranychus evansi Baker & Pritchard) was also assessed. The Tetranychidae (Acari) contain some of the most important pest species of phytophagous mites worldwide. Out of the almost 1,300 species in this family, 256 species are known to occur in Africa. Before this study, ten species had been reported from Kenya and only three in Tanzania. The genus Tetranychus to which most of the pest species belongs to, can only be identified to species level by the use of the male aedeagus that is often difficult to visualize. The natural habitat, the Eastern Arc Mountains and East African Coastal Forests in Kenya and Tanzania is recognized as biodiversity hotspots but prior to his study, information on Tetranychidae in these hotspots was lacking. Thus, no information on the natural mite fauna composition was available. In Kenya, 18 tetranychid mite species from various plant hosts have been recorded. Four of these species belong to the subfamily Bryobiinae and the other 14 to the subfamily Tetranychinae. Eight of the mite species identified belong to the genera Bryobia, Petrobia, Peltanobia, Paraplonobia, Duplanychus, Eutetranychus and Mixonychus and are being reported for the first time in Kenya while the other ten had already been reported before. For Tanzania, six species belonging to the genera Tetranychus, Eutetranychus and Mixonychus are being reported for the first time from Tanzania and other three had been reported before. A list of these species, their brief descriptions as well as a key for identification is provided. A redescription of Peltanobia erasmusi including previously undescribed male characters is given. Schizotetranychus kwalensis sp. nov. from Kenya and Brevinychus meshacki from Tanzania were collected on Omorcarpum kirkii (Fabaceae) from Matuga, Kwale district, Kenya and Philonoptera eriocalyx (Fabaceae) from Sangasanga, Mvomero district, Tanzania respectively and described. Revised keys of Brevinychus and of the African species of Schizotetranychus are also provided. Tetranychus evansi Baker & Pritchard ranked highest in abundance amongst all the tetranychid mites collected. It was found in four out of five fragments of the hotspot, and it survives in a wide range of altitudes from as low as 123 m to 1655 m. Molecular examination of T. evansi collected from Kenya and Tanzania and on different host plants revealed an identical DNA sequence of the mitochondrial COI fragment and 19 identical microsatellite alleles suggesting a single introduction of this species to this part of East Africa. Female characters of four Tetranychus species found in Kenya were explored using the scanning electron microscope. Differences in the distances between the duplex setae of species belonging to the desertorum group (Tetranychus evansi Baker & Pritchard and Tetranychus ludeni Zacher) and those grouped by Flechtmann and Knihinicki (2002) under group 9 (Tetranychus neocaledonicus Andre and Tetranychus urticae Koch) were observed. The dorsal striae of T. evansi, T. neocaledonicus and T. urticae have semicircular lobes whereas those on the dorsal striae of T. ludeni are triangular. / Thesis (PhD (Environmental Sciences))--North-West University, Potchefstroom Campus, 2012.

The aims of this study were to develop a detailed record of the tetranychid mites of Kenya and Tanzania, to assess the diversity of tetranychid mites in the east African biodiversity hotspots and to determine female characters that can be used to identify the species of the economically important Tetranychus species found in these countries. The genetic diversity of the most abundant Tetranychus species (Tetranychus evansi Baker & Pritchard) was also assessed. The Tetranychidae (Acari) contain some of the most important pest species of phytophagous mites worldwide. Out of the almost 1,300 species in this family, 256 species are known to occur in Africa. Before this study, ten species had been reported from Kenya and only three in Tanzania. The genus Tetranychus to which most of the pest species belongs to, can only be identified to species level by the use of the male aedeagus that is often difficult to visualize. The natural habitat, the Eastern Arc Mountains and East African Coastal Forests in Kenya and Tanzania is recognized as biodiversity hotspots but prior to his study, information on Tetranychidae in these hotspots was lacking. Thus, no information on the natural mite fauna composition was available. In Kenya, 18 tetranychid mite species from various plant hosts have been recorded. Four of these species belong to the subfamily Bryobiinae and the other 14 to the subfamily Tetranychinae. Eight of the mite species identified belong to the genera Bryobia, Petrobia, Peltanobia, Paraplonobia, Duplanychus, Eutetranychus and Mixonychus and are being reported for the first time in Kenya while the other ten had already been reported before. For Tanzania, six species belonging to the genera Tetranychus, Eutetranychus and Mixonychus are being reported for the first time from Tanzania and other three had been reported before. A list of these species, their brief descriptions as well as a key for identification is provided. A redescription of Peltanobia erasmusi including previously undescribed male characters is given. Schizotetranychus kwalensis sp. nov. from Kenya and Brevinychus meshacki from Tanzania were collected on Omorcarpum kirkii (Fabaceae) from Matuga, Kwale district, Kenya and Philonoptera eriocalyx (Fabaceae) from Sangasanga, Mvomero district, Tanzania respectively and described. Revised keys of Brevinychus and of the African species of Schizotetranychus are also provided. Tetranychus evansi Baker & Pritchard ranked highest in abundance amongst all the tetranychid mites collected. It was found in four out of five fragments of the hotspot, and it survives in a wide range of altitudes from as low as 123 m to 1655 m. Molecular examination of T. evansi collected from Kenya and Tanzania and on different host plants revealed an identical DNA sequence of the mitochondrial COI fragment and 19 identical microsatellite alleles suggesting a single introduction of this species to this part of East Africa. Female characters of four Tetranychus species found in Kenya were explored using the scanning electron microscope. Differences in the distances between the duplex setae of species belonging to the desertorum group (Tetranychus evansi Baker & Pritchard and Tetranychus ludeni Zacher) and those grouped by Flechtmann and Knihinicki (2002) under group 9 (Tetranychus neocaledonicus Andre and Tetranychus urticae Koch) were observed. The dorsal striae of T. evansi, T. neocaledonicus and T. urticae have semicircular lobes whereas those on the dorsal striae of T. ludeni are triangular. / Thesis (PhD (Environmental Sciences))--North-West University, Potchefstroom Campus, 2012.

Tetranychus urticae es una especie plaga importante en cítricos que puede también alimentarse de otras especies asociadas a la cubierta vegetal de este cultivo. Para determinar el efecto de la gestión de la cubierta vegetal en el control biológico de este ácaro, hemos estudiado la dinámica tanto de ácaros Tetranychidae como Phytoseiidae en cuatro parcelas comerciales de mandarino clementino en las que se aplicó tres estrategias diferentes de gestión de la cubierta vegetal: (1) suelo desnudo, (2) cubierta espontánea y (3) cubierta sembrada de Festuca arundinacea. Los resultados apuntan a que tanto los enemigos naturales (mecanismos "top-down") como la planta huésped (mecanismos "bottom-up") juegan un papel importante en la regulación de los ácaros Tetranychidae. Por un lado, la selección de dos razas de T. urticae especializadas en F. arundinacea y en Citrus clementina, en la cubierta y en el árbol respectivamente, cuando esta gramínea se utiliza como cubierta podría explicar en parte los resultados obtenidos (regulación "bottom-up") ya que esto impediría a los especímenes de una planta huésped colonizar con éxito la otra. Los ensayos de trasplante recíproco realizados muestran que las dos demos de T. urticae recogidas de clementina y F. arundinacea difieren considerablemente en su éxito en el desarrollo en el huésped alternativo y esto indica la existencia de fenómenos de adaptación local. Esta adaptación se traduciría en mecanismos "bottom-up" que evitarían que los ácaros que habitan en la cubierta colonicen con éxito la copa de los árboles. Por otro lado, la composición cualitativa de las comunidades de Phytoseiidae asociados a las diferentes cubiertas podría ser clave en la regulación de las poblaciones de T. urticae y Panonychus citri (regulación "top-down"). Los ácaros Phytoseiidae tipo I y II, depredadores especializados en Tetranychidae, se encuentran de manera consistente en la cubierta de F. arundinacea y esto puede explicar la mejor regulación de las poblaciones de ácaros Tetranychidae en los árboles asociados a esta cubierta. Por el contrario, la disposición más regular de fuentes de alimentación alternativas (polen) en la cubierta natural en relación con la cubierta de F. arundinacea, podría explicar la mayor abundancia de Phytoseiidae tipo IV en la primera. Como consecuencia, los Phytoseiidae tipo I y II, más eficaces en el control de Tetranychidae, podrían sufrir las consecuencias de ser competitivamente inferiores que el Phytoseiidae generalista tipo IV que explota el polen en la cubierta espontánea. Este hecho, en combinación con los períodos de escasez de presa, podría dar lugar a su desaparición del agroecosistema y resultar en un deficiente control de los ácaros Tetranychidae en los árboles asociados a una cubierta natural. Haciendo balance de gastos e ingresos, la cubierta más favorable fue la de F. arundinacea (entre 44,4 y 74,5% de reducción de costes en relación con la más cara). Festuca arundinacea como cubierta vegetal es una estrategia de control biológico por conservación muy recomendable para los productores de clementina. Aunque su uso no redujo las poblaciones de ácaros en los árboles por debajo del umbral económico, la disminución en la necesidad de tratamientos, hace que la adopción de esta táctica sea una alternativa beneficiosa tanto ecológica como económicamente. Nuestros resultados apuntan a la cubierta de F. arundinacea, que no permitió el establecimiento de Tetranychus evansi y ofrece una mejor regulación de P. citri y T. urticae que en suelo desnudo o cubierta natural, como la más adecuada para un control más sostenible de los ácaros Tetranychidae en cítricos.