Plant Strata Research Articles

Efectos ecológicos del fuego sobre la avifauna de un bosque en El Salvador

Con el objetivo de evaluar los efectos ecológicos causados por los incendios forestales sobre la avifauna del bosque seco caducifolio en el parque Walter Thilo Deininger, en El Salvador establecí cuatro puntos de conteo en cada zona de estudio basado en el tiempo desde el fuego (Z1 = cinco años, Z2 = dos años y Z3 = un año). La prueba t de Hutcheson determinó que las zonas recién afectadas mantuvieron una diversidad de aves significativamente más grande que la zona con mayor tiempo desde el fuego (Z1-Z2 t = 5.198, gl = 208, P < 0.01; Z1-Z3 t = 5.499, gl = 170, P < 0.01). Los números efectivos de especies reforzaron esta premisa. El índice de Sørensen cuantitativo demostró que la similitud entre pares de zonas fue de baja a moderada (Z1-Z2 31%; Z1-Z3 48%; Z2-Z3 52%), lo cual fue consistente con la alta diversidad que hallé, dado que pocas especies fueron compartidas entre zonas. Con el análisis de correspondencia encontré una asociación significativa entre los gremios tróficos estudiados y el estrato vegetal característico de cada zona (x2 = 143.0521, P < 0.01). Mis resultados aportan evidencia de que los incendios forestales han favorecido la diversidad avifaunística del parque y además que el uso de los gremios tróficos es útil en el estudio comparativo de comunidades de aves.

Sampling procedures and action threshold level of vectors of viruses that cause maize lethal necrosis disease in Kenya

Maize lethal necrosis disease (MLND) has emerged as a major threat to maize production in East Africa. The disease is caused by a co-infection of maize by maize chlorotic mottle virus (MCMV) and sugarcane mosaic virus (SCMV) which are respectively vectored by corn thrips, Frakliniella williamsi Hood and corn leaf aphids, Rhopalosiphum maidis Fitch. Developing a reliable and practical sampling plan and action threshold for population monitoring of the two vectors is key for implementing a reliable integrated vector management strategy. A study was carried out to determine the sampling regime and action threshold levels for the vectors. Three maize stratas (upper, mid and lower foliage levels), three sampling intervals and five spray regimes using Thunder OD 145 (110 g/L Imidacloprid and 100 g/ L Betacyfluthrin 45 g/L) (were tested. The upper plant strata proved a preferred target for corn thrips (P < 0.001) while the lower section was preferred by corn leaf aphids during season 2(P = 0.03). Scouting at 8.30 to 10.30 am (P = 0.04) gave a better estimation of the vector infestation. Corn thrips infestation was significantly lower on maize sprayed on a weekly regime (P = 0.01). However, maize crop from thunder sprayed plots was MLND negative while the unsprayed maize crop was positive (P < 0.001). Although the yield from weekly sprayed plots was higher than any other treatments (P < 0.001), the net returns from monthly sprayed plots was higher. The action threshold level for corn thrips and corn leaf aphids was found to be six and three per plant respectively. These findings provide information on how, when and where to scout and spray for the two vectors. This may eventually lead to minimal wide spread of the virus by the vectors.

Sistema imune inato de peixes e o uso do alho como imunoestimulante: revisão de literatura

O objetivo desta revisão de literatura é evidenciar os principais aspectos do sistema imune inato dos peixes demonstrando a necessidade de novas alternativas para controle de enfermidades, respeitando a premissa da sustentabilidade, com o uso de imunoestimulantes biologicamente ativos. Nos peixes não há presença de tecidos ou órgãos mieloides, os componentes do seu sistema imune são classificados apenas como linfoides, ou seja, a imunidade inata, é considerada a primeira linha de defesa do organismo frente ao patógeno. Dessa forma, o uso de aditivos alimentares e imunoestimulantes auxiliam a melhorar o sistema imune natural desses animais. Podem ser substâncias sintéticas, químicas ou biológicas que induzem a ativação ou aumento de componentes do sistema imune, proporcionando assim defesa precoce contra enfermidades, podendo ser utilizado como tratamento preventivo. Os compostos vegetais, óleos essenciais e estrato de plantas bioativas tem grande potencial, pois possuem funções antimicrobianas e antiparasitária comprovadas. Dentre eles, o alho é apontado como um dos mais eficazes, por atuar como promotor de crescimento, estimulador de apetite, antimicrobiano, antioxidante e imune estimulante, ajuda ainda em parâmetros hematológicos e aumentando o bem-estar dos peixes, bem como, capacidade de melhorar a qualidade da carne e estender o tempo de prateleira.

A predatory mite, Amblyseius swirskii, and plastic mulch for managing melon thrips, Thrips palmi, in vegetable crops

Melon thrips, Thrips palmi Karny (Thysanoptera: Thripidae), is a significant pest of vegetable crops and ornamental plants due to feeding and oviposition injury to vegetative and reproductive tissues. As an integrated approach, we evaluated the efficacy of a phytoseiid mite, Amblyseius swirskii Athias-Henriot, and different colored and UV-reflective plastic mulches for managing T. palmi in snap bean (Phaseolus vulgaris L.), cucumber (Cucumis sativus L.), yellow squash (Cucurbita pepo L.), eggplant (Solanum melongena L.), Jalapeño pepper (Capsicum annuum L.), and tomato (Solanum lycopersicum L.). The five mulch treatments evaluated were: “Shine N′ Ripe” (Metalized top and black bottom), “Can-Shine” (Metalized top and white bottom), “Black” plastic black-on-black (Can-Grow-XSB), black-on-white (Can-Grow XSB), “White” plastic; white-on-black (Can-Grow XSB), and bare soil with no mulch. The number of T. palmi adults and larvae in leaf samples collected from the middle third (stratum) of plants in each treatment was determined. In 2015 at 49 days after planting (DAP), curative release of 40–50 A. swirskii per plant did not suppress T. palmi effectively when the thrips population was high. There were no significant interactions between A. swirskii and crop or A. swirskii and mulch type on the number of T. palmi. However, in 2016 at 15 DAP, preventive release of A. swirskii, reduced the number of T. palmi in each of the mulch and crop treatments. Metalized mulch reduced the number of T. palmi early in the season when plants’ canopy did not shade the mulched area. These results suggest that use of metalized reflective mulch and A. swirskii, each have the potential to manage T. palmi at low population densities.

Efeitos de atributos ambientais na biodiversidade de formigas sob diferentes usos do solo

O objetivo foi avaliar a influência de variáveis ambientais sobre a fauna de formigas em um fragmento de floresta nativa e em áreas sob cultivo orgânico. Os dados foram coletados no município de Seropédica-RJ, nas estações chuvosa e seca, nas seguintes áreas: plantação de bananas (Musa pariadisiaca L.); agrofloresta; cafezal (Coffea conephora Pierre) sombreado com Gliricidia sepium (Jacq.); fragmento de floresta (8 ha) em estágio intermediário de sucessão secundária. Para a amostragem, foram utilizadas cinco unidades amostrais por área, cada uma composta por três armadilhas de queda tipo pitfall e uma parcela de 1 m² onde foi extraída a cobertura morta/ serapilheira, que foi peneirada e alocada no extrator de Winkler. Foram coletadas 53 espécies de formigas, ocorrendo maior riqueza de espécies na agrofloresta (38 espécies), seguida do cafezal (31 espécies), floresta secundária (29 espécies) e plantação de bananas (28 espécies). Na estação seca houve o efeito do tipo de uso do solo e da profundidade de serapilheira sobre a riqueza e diversidade de espécies de formigas. Nas duas estações, a composição de espécies de formigas variou significativamente entre todas as áreas estudadas. O aumento da heterogeneidade estrutural do ambiente e da profundidade de serapilheira em áreas cultivadas proporcionou maior riqueza e diversidade de espécies de formigas, além de mudanças na composição de espécies. Desta forma, pela diversidade de espécies cultivadas e estratos vegetais que apresentam, os sistemas agroflorestais funcionam como alternativa às monoculturas. Principalmente, no que se refere à proteção da biodiversidade, já que estes ambientes apresentam maior disponibilidade de recursos alimentares e de locais para a nidificação, não somente para a fauna de formigas.

Biology and host selection stage of Symmetrischema dulce Povolny (Lepidoptera: Gelechiidae) in chili pepper.

The pepper-fruit-borer Symmetrischema dulce Povolny (Lepidoptera: Gelechiidae) is an important chili pepper pest causing significant yield losses. However, chili pepper has insufficient crop protection support and primary information about S. dulce is scarce. In the present study, we aimed to study the biology and ecology of S. dulce in pepper plants (Capsicum frutescens L.) focusing to support integrated pest management programs. In the field, we sampled ripe and unripe chili pepper fruits in three different plant strata. In the laboratory, we established colonies of the S. dulce and we recorded the duration, viability, morphology of each life stage, and number of larval instars. We conducted experiments to evaluate insect reproduction, whereby we registered the pre-oviposition and oviposition period, daily oviposition rate, and sex ratio. From these results, we estimated the reproductive success of S. dulce through the intrinsic population growth rate. The higher occurrence of S. dulce was in unripe fruits with no difference between plant strata. Egg stage lasted 4days with 94% viability, and larval phase lasted on average 10.72days and presented four instars with viability of 66.6%. Pupal stage lasted 9.61days with viability of 94.73%. The adult stage lasted 24.14days with a pre-oviposition period of 3days and oviposition period of 13.85days. The intrinsic growth rate (rm) recorded was 0.0035. Our results suggest that the biology of S. dulce has similarities with other Lepidoptera, but its peculiarities in reproductive parameters are essential for future programs of pest management.

Adaptive Agroforestry Model To Improve Livelihood And To Support The Management Of Minraleng Watershed In Maros Regency

Many watershed area in Indonesia and South Sulawesi experience erosion, flood and landslide in rainyseason and in dry season experience drought, like in Minraleng Watershed. This condition have impacted to food insecurity of the community that reside in watershed area. This study aim to formulate adaptive agroforestry model to increase farmer livelihood in supporting watershed management. Population study i.e. all of the farmer household in Minraleng Hulu Watershed. Study sampling was done by purposive sampling in 4 sampling village (Limampoccoe, Cenrana Baru, Timpuseng and Batu Putih). Data collection was done by in-depth interview and observation. Data was analyzed by qualitative descriptive and spatial analysis. Result of the study indicated that combination pattern of landscape agroforestry model need to be developed in dry land and the big property land in Cenrana Baru, Limampoccoe and Batu Putih. That agroforestry model known by Taungya by developing adaptive plant to drought and give livelihood diversification and adaptive to the short rainy season, secure from pest i.e. swine, monkey, and cow. In Timpuseng village, agroforestry pattern need to be was permanent intensive agroforestry which is known by Talun where farmer need to develop three to fourth strata of plant to resolve limited land by planting gamal tress and candlenut in the top of the strata, while planting coffee and pepper in second strata, and chili and elephant grass in third strata. Intensive permanent agroforestry with low labour input to resolve limited farmer labour which dominant in rice field

Intra-Plant Distribution and Population Fluctuation of Raoiella indica Hirst (Acari: Tenuipalpidae) on Coconuts in the State of Falcón, Venezuela

Knowledge of the ecology of the red palm mite, Raoiella indica Hirst, is still fragmentary in South America since it was only recently introduced from East Asia. Gathering intra-plant distribution and population fluctuation data could contribute to developing more efficient sampling methods for R. indica. Taking this into consideration, studies were carried out to determine spatial temporal distribution of R. indica in three commercial plantations in the state of Falcon, in Venezuela. Higher mite numbers were registered on middle and lower leaf portions collected from middle or lower plant strata, suggesting that sampling should be allocated to these canopy areas on coconut trees. The R. indica population showed to be negatively associated with rainfall. In 2010, population levels of R. indica were higher than in 2011 (maximum 7 mites/cm2); this was probably a function of lower rainfall values for that year. In 2011, the highest population levels were reached between April and July, coinciding with the lowest rainfall values over that year. Relating to this population spike, the Amblyseius largoensis population showed a numerical response in relation to R. indica density; this predator species does not appear to be exerting bio-control on the mite pest population.

Peatland vegetation change and establishment of re-introduced Sphagnum moss after prescribed burning

Fire, including prescribed burning, is common on peatlands globally and can affect vegetation, including peat-forming Sphagnum mosses, and affect ecosystem services. We monitored vegetation in different burn-age categories at three UK peatland sites over a 19-month period. Half of the plots had Sphagnum fragments added and their survival was assessed. Changes in vegetation composition over time, and associations between vegetation composition, site and burn-age category were investigated. Plots in the most recently burned category were likely to have more bare peat, a thinner moss layer and lower vascular plant strata. Graminoid cover initially increased after burning but was low after 10 + years. Dwarf shrub cover increased after burning and remained high after 10 + years. At the most Sphagnum-rich site, a high proportion of existing Sphagnum cover was bleached one year after burning, but recovery occurred during the study period. Sphagnum re-introduction success decreased over the study period in the most recent and intermediate burn-age categories at the most Sphagnum-poor site. These results show that burning rotation length is an important factor in determining site-level vegetation composition on burned sites. More frequent burning will result in a greater proportion of land in the early post-burning stages, potentially resulting in a thinner moss layer, more bare peat and less healthy Sphagnum, with potential consequences for carbon balance. No evidence was found to support the use of burning as a tool to increase existing Sphagnum or promote Sphagnum re-establishment success.

Desempeño agronómico y valor nutritivo de Tithonia diversifolia (Hemsl.) A Gray para la alimentación de bovinos

La producción ganadera tradicional debido a la presión ejercida sobre los recursos, debe sufrir una transformación que incluya elementos que permitan la sostenibilidad de la actividad en el entorno productivo. La implementación de sistemas silvopastoriles se constituye en una alternativa viable para el mejoramiento de la producción a través de la inclusión de especies leñosas en el potrero para la formación de diferentes estratos, que generen múltiples beneficios a todos los elementos del ciclo bovino. La selección de las especies silvopastoriles debe ser realizada teniendo en cuenta aspectos agronómicos y composicionales para optimizar la respuesta animal. Este documento presenta una revisión sobre el potencial agronómico, la calidad nutricional y el uso del Botón de oro (Tithonia diversifolia – Asteraceae) en la alimentación de bovinos. Se describen las principales formas de establecimiento, contenido de nutrientes, producción de biomasa, acción en el suelo debido a su uso como abono verde y sus efectos productivos en la dieta de los rumiantes. El establecimiento del Botón de oro (Tithonia diversifolia), puede ser realizado a través de semilla sexual y vegetativa. Su composición nutricional muestra niveles elevados de proteína y carbohidratos solubles, bajo contenido de FDN, y niveles adecuados de minerales, su establecimiento y uso como abono verde puede mejorar las condiciones de fertilidad del suelo para aumentar la producción y rendimiento del pasto. Estas características le confieren una alto potencial en la alimentación bovina, ya sea como recurso para ramoneo, procesado en harina o ensilado, para reducir los costos de producción en explotaciones ganaderas.

Vegetation Indices to Estimate Spray Application Rates of Crop Protection Products in Corn

Spray deposition in corn crop is related to the vegetation indices. Spray deposition in corn crop is related to the spray application rate. Plant stand density has no influence on the spray deposition. Determination of the spray application rates (SAR) of crop protection products for different crops is subjective. The study aimed to develop an equation to estimate optimal spray application rates using a vegetation index (VI) and an expected relative spray deposition for summer corn crop. An experiment was performed in the crop year 2015 to 2016, and 2016 to 2017, with a plant density of 60,000 plants ha−1 with 0.45‐m row spacing, under the no‐tillage system, in the municipality of Chapadão do Sul. An active multispectral sensor (Crop Circle ACS‐470) was used to obtain the VI Red Edge, Normalized Difference Red Edge (NDRE), and Normalized Difference Vegetation Index (NDVI), using the red, red edge, and near‐infrared bands. The experiment consisted of plots subdivided in a 4 × 4 factorial scheme (four spray application rates and four phenological stages), with four replications for each treatment. The mass balance analysis measured leaf deposits. The relationship between vegetation index values and middle stratum deposits showed a quadratic trend. When the vegetation index values are increased, the spray application rate (from 40 to 100 L ha−1) needs to also increase to maintain the same spray deposition (from 50 to 100%) in the middle stratum of corn plants. The vegetative indices studied (VI Red Edge, NDRE, and NDVI) positively correlated to the spray deposition in the middle stratum of corn plants, which also depends on the SAR. Furthermore, the relationship between vegetation index and spray deposits need to be studied for other crops, plant architecture, and stand density.

Systems and rates of aerial application of fungicides in irrigated rice

ABSTRACT The present research studied the performance of flat-fan and hollow-cone nozzles, with application rates of 20 and 30 L ha-1, and rotary disc atomizer with application rates of 10 and 15 L ha-1. The test was conducted with a fungicide spray tank composed of Azoxystrobin + Difenoconazole, in which the density and penetration of droplets into the canopy were evaluated using a water-sensitive paper and the distribution of the active ingredients in the plant was evaluated through the chromatographic analysis. Higher application rates resulted in higher droplet density in the upper stratum of plants. In all treatments, the penetration of the droplets was 26% into the middle stratum and 23% into the lower stratum, in relation to the top of the crop, resulting in an average 25% penetration of droplets into the leaf canopy. The active ingredients were distributed in greater quantity in the upper stratum of the plant. For the same weight, the upper part of the ‘Puitá Inta CL’ rice cultivar has a leaf area 6.4 times larger than the lower part. It was concluded that higher application rate leads to higher droplet density in the upper stratum of the leaf canopy and that all systems and application rates promoted similar penetration of droplets into the canopy.

Behaviour‐driven micro‐scale niche differentiation in carabid beetles

AbstractCarabid beetles form rich and abundant communities in arable landscapes. Their generalist feeding behaviour and similar environmental requirements raise questions about the mechanisms allowing the coexistence of such species‐rich assemblages. We hypothesized that subtle niche partitioning comes into play on spatial, temporal, or trophic basis. To test this, we performed experiments and made observations on the behaviour of two sympatric carabid species of similar size and life cycle, Bembidion quadrimaculatum L. and Phyla obtusa Audinet‐Serville (both Coleoptera: Carabidae: Bembidiini). We compared plant climbing behaviour, daily activity patterns, and trophic preferences between the two carabid species under laboratory conditions. Whereas no clear difference in trophic preference was observed, our results suggest temporal niche differentiation at the nychthemeron scale (a period of 24 consecutive hours), with one of the species being more diurnal and the other more nocturnal, and spatial differentiation in their habitat use at the plant stratum scale. Intra‐specific variation suggests that micro‐scale spatio‐temporal niche differentiation could be mediated by behavioural plasticity in these two carabid species. We speculate that such behavioural plasticity may provide carabid beetles with a high adaptive potential in intensively managed agricultural areas.

Within-plant distribution of Aulacorthum solani (Hemiptera: Aphididae), on various greenhouse plants with implications for control.

Foxglove aphid, Aulacorthum solani (Kaltenbach) (Hemiptera: Aphididae), has recently undergone a status change from an occasional pest to a serious pest in greenhouses of North America and the United Kingdom. Little nonanecdotal information exists on the ecology of this insect in greenhouse crops. To help improve integrated pest management decisions for A. solani, the within-plant distribution of this pest was explored on a variety of common greenhouse plants in both the vegetative and flowering stage. This aphid generally was found on lower leaves of vegetative plants, but was found higher in the canopy on reproductive plants (on flowers, flower buds, or upper leaves). Aphid numbers were not consistently positively correlated with total leaf surface areas within plant strata across plant species. Thus, the observed differences in preferred feeding sites on vegetative versus flowering plants are possibly a response to differences in nutritional quality of the various host-plant tissues. Despite being anecdotally described as a "stem-feeding aphid," A. solani was rarely found feeding on stems at the population densities established in our tests, with the exception of racemes of scarlet sage (Salvia splendans). Although some previous reports suggested that A. solani prefers to feed on new growth of plants, our results indicate that mature leaves are preferred over growing tips and young leaves. The implications of the within-plant feeding preferences of A. solani populations with respect to both biological and chemical control are discussed.

Effect of Selected Insecticides onLygus hesperus(Heteroptera: Miridae) Oviposition Behavior in Cotton

Oviposition behavior of western tarnished plant bug, Lygus hesperus Knight, as affected by residual insecticides, was studied in potted as well as field-grown cotton. In this study, we investigated the spatial distribution and phytotomical preference of Lygus oviposition in presquaring and blooming cotton, as affected by selected insecticides. Flonicamid, acephate, and cypermethrin were applied to cotton at 82, 516, and 114 g (active ingredient)/ha, respectively. At 3 d posttreatment, a gravid female Lygus was caged on the plants. After 4 d, caged plants were harvested and eggs were counted by whole plant dissection. Results indicated significantly greater egg deposition in untreated controls than treated plants in both potted and field-grown cotton. For untreated plants, Lygus preferred to oviposit on the pulvinus and leaf petiole, where 76 and 85% of eggs were laid in potted and field-grown cotton, respectively. For insecticide-treated plants, no plant structure preference was observed, although fewer eggs were laid. The upper stratum of the plant canopy had significantly more eggs than the lower or middle strata of untreated plants, while more eggs were observed in the middle strata of plants treated with acephate in field-grown cotton. Sublethal effects could not be adequately assessed in the cypermethrin treatment owing to high Lygus mortality.

An accurate record of volcanic ash fall deposition as characterized by dispersed organic matter in a lower Permian tonstein layer (Faxinal Coalfield, Paraná Basin, Brazil)

For the first time, the dispersed organic matter in the tonstein layer interbedded with a coal seam in the Faxinal Coalfield (Sakmarian, Southern Parana Basin, Brazil) is characterized. The deposition of clusters of pollen grains was highly influenced by the intense ash fall process that probably occurred during seasonal dehiscence of reproductive structures. The well-preserved phytoclasts with their upper and lower leaf cuticles stuck together indicate that the rapid fall of ash on this material hindered organic biodegradation. The preservation of seemingly autochthonous Botryococcus colonies at the top of the tonstein layer is evidence of the subaqueous deposition of this layer. The darkening in cuticles and xylem phytoclasts can be attributed to different causes: the thermal influence of ash fall during deposition, chemical effects of the ash, prolonged oxidation of organic matter in low water level conditions or the burning of plant organs by wildfires. Analyses of dispersed organic matter along the tonstein layer showed that the organic matter succession reflects the composition of different plant strata (herbaceous pteridophytes and arboreal glossopterids-cordaitaleans) around the deposition site.

Responses of Whitefly, Bemisia tabaci (Genn.) (Homoptera: Aleyrodidae) Population on Tomato Lycopersicon esculentnm Mixed with Other Crops under Glasshouse Conditions

The whitefly Bemisia tabaci is one of the most important pests of the tomato Lycopersicon esculentnm in the world; it affects plant vigour, transmits geminiviruses and reduces crop quality. This experiment was conducted to determine the response of Bemisia tabaci population when tomato (Solanum lycopersicum MT1) planted alone (non-choice), tomato planted with brinjal (Solanum malagna MTe1), tomato with chilli (Capsicum annuum MC11), tomato with okra (Abelmoschus esculentus MKBE1), and all together (choice experiment) under glasshouse conditions (30-36°C, 80% RH). The results have shown that, there were significantly higher (P< 0.05) numbers of adults, eggs and nymphs on tomato alone or planted with chilli, whereas significantly lower numbers of adults, eggs and nymphs were seen when tomato was planted with okra and brinjal. Generally, the number of adults and eggs was observed to be more on the upper stratum compared to the lower plant stratum. Interestingly, the number of nymphs was found to be higher on the middle stratum than on the other strata in all treatments.

The influence of intraguild competitors on reproductive decisions by two predatory Heteroptera, Orius insidiosus (Anthocoridae) and Nabis americoferus (Nabidae)

The relationship between the oviposition site preferences of predators in the face of intraguild competitors has received little attention, but it likely shapes the reproductive ecology of predatory species. In this study, oviposition intensity and the within-plant distribution of Orius insidiosus (Heteroptera: Anthocoridae) and Nabis americoferus (Heteroptera: Nabidae) eggs on Phaseolus vulgaris plants was studied when the two species were present independently or in combination. Both predators laid more eggs in the presence of the other species relative to when they were only exposed to conspecifics. When only exposed to conspecifics, O. insidiosus preferred to lay eggs on leaves and petioles on the upper half of the plant, whereas N. americoferus laid eggs mostly on the petioles and petiolules equally throughout the height of the plant. But when both species were present, O. insidiosus preferred to lay eggs on the leaf, whereas N. americoferus altered their behavior to lay an even greater proportion of their eggs on the petioles and petiolules. They altered their preferences for different plant strata too: N. americoferus laid more eggs on the upper quarter of the plant when O. insidiosus was present, and O. insidiosus was marginally more likely to lay eggs lower on the plant in the presence of N. americoferus. This study indicates that these two Cimicomorpha can detect the presence of one another, and that they adjust their reproductive decisions, presumably to avoid potential competitive interactions.

Distributions of western flower thrips (Thysanoptera: Thripidae) and its predatory bug Orius niger (Hemiptera: Anthocoridae) assessed by coloured sticky traps and plant samplings in cotton

The capturing efficiency of four coloured (yellow, green, white and blue) sticky traps, placed at the top, middle and bottom strata of cotton plants, was tested for the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), and its predatory bug, Orius niger (Wolff) (Hemiptera: Anthocoridae), as well as spatial distributions of both insects on the plant in years 2006 and 2007. The white coloured trap was the most attractive to F. occidentalis and O. niger in the 2-year study. The blue coloured trap was the least attractive for Orius. The mean numbers of F. occidentalis and O. niger on the top plant parts (flowers and leaves) and in all coloured traps positioned on the upper parts of the plants were greater than those found in the lower two strata. Taylor's power law analysis showed that F. occidentalis and O. niger adults aggregated in the flowers or on the leaves. This study suggests that top flowers could be preferentially sampled to determine population densities of Frankliniella flower thrips and Orius species in cotton, and thus, sticky traps should be placed on the top level of plants. F. occidentalis: O. niger ratios in the flowers varied from 4 to 60 thrips per Orius adult in the three plant strata. This result may indicate that F. occidentalis experiences more predation from Orius.

Tuberous root yield of Dahlia variabilis Wild (Desf.) under different agronomic management practices

The Dahlia variabilis Wild (Desf.) is considered the Mexican national flower and their exploitation is mainly for ornamental purposes. Recent studies have shown that the tuberous roots dry weight of this species contains from 38 to 53% of a polysaccharide of fructose called inulin. The consumption of this compound does not elevate the levels of glucose in the blood of human beings, making this polysaccharide an attractive product for the food industry. This fact has helped to diversify (1) the production of Dahlia variabilis and (2) research towards the production of their roots. The aim of this study was to evaluate the effect of phosphorus fertilization, planting density and leaf removal on dry matter production of roots of Dahlia variabilis. In spring-summer 2009, two experiments were established. In the first study, we evaluated four phosphorus levels (0, 60, 100 and 120 kg P2O5/ha) and four planting densities (2.5, 3.12, 4.16 and 6.25 plants/m2) under a factorial arrangement in a randomized complete block design with four replications. In the second study, the source-sink relationship was evaluated defoliating different plant strata. The treatments were: undefoliated (t1), defoliated the lower stratum (t2), the intermediate stratum defoliated (t3), defoliated the upper stratum (t4), defoliated the lower and middle strata (t5), defoliated the lower and upper strata (t6), defoliated the middle and upper strata (t7), and completely defoliated (t8). These treatments were distributed in a randomized complete block design with four replications. The results showed significant differences in the factors phosphorus and planting density. The highest production of root dry matter (345 g/m2) was achieved with 120 kg/ha of phosphorus and 6.25 plants/m2. Leaf removal revealed that the middle and lower strata (66%) satisfied the “sink” from the root.