Impact of small variations in temperature and humidity on the reproductive activity and survival of Aedes aegypti (Diptera, Culicidae)

In short space of time increase in temperature and rainfall can affect vector populations and, consequently, the diseases for them transmitted. The present study analyzed the effect of small temperature and humidity variations on the fecundity, fertility and survival of Aedes aegypti. These parameters were analyzed using individual females at temperatures ranging from 23 to 27 °C (mean 25 °C); 28 to 32 °C (mean 30 °C) and 33 to 37 °C (mean 35 ºC) associated to 60±8% and 80±6% relative humidity. Females responded to an increase in temperature by reducing egg production, oviposition time and changing oviposition patterns. At 25 ºC and 80% relative humidity, females survived two-fold more and produced 40% more eggs when compared to those kept at 35 ºC and 80% relative humidity. However, in 45% of females kept at 35 ºC and 60% relative humidity oviposition was inhibited and only 15% females laid more than 100 eggs, suggesting that the intensity of the temperature effect was influenced by humidity. Gradual reductions in egg fertility at 60% relative humidity were observed with the increase in temperature, although such effect was not found in the 80% relative humidity at 25 º C and 30 º C. These results suggest that the reduction in population densities recorded in tropical areas during seasons when temperatures reach over 35 ºC is likely to be strongly influenced by temperature and humidity, with a negative effect on several aspects of mosquito biology.

The effect of environment on development and survival of pupae of the necrophagous fly Ophyra albuquerquei Lopes (Diptera, Muscidae)

The effect of environment on development and survival of pupae of the necrophagous fly Ophyra albuquerquei Lopes (Diptera, Muscidae). Species of Ophyra Robineau-Desvoidy, 1830 are found in decomposing bodies, usually in fresh, bloated and decay stages. Ophyra albuquerquei Lopes, for example, can be found in animal carcasses. The influence of environmental factors has not been evaluated in puparia of O. albuquerquei. Thus, the focus of this work was motivated by the need for models to predict the development of a necrophagous insect as a function of abiotic factors. Colonies of O. albuquerquei were maintained in the laboratory to obtain pupae. On the tenth day of each month 200 pupae, divided equally into 10 glass jars, were exposed to the environment and checked daily for adult emergence of each sample. We concluded that the high survival rate observed suggested that the diets used for rearing the larvae and maintaining the adults were appropriate. Also, the data adjusted to robust generalized linear models and there were no interruptions of O. albuquerquei pupae development within the limits of temperatures studied in southern Rio Grande do Sul, given the high survival presented.

Population growth and within-plant distribution of the striped mealybug Ferrisia virgata (Cockerell) (Hemiptera, Pseudococcidae) on cotton

Population growth and within-plant distribution of the striped mealybug Ferrisia virgata (Cockerell) (Hemiptera, Pseudococcidae) on cotton. The striped mealybug, Ferrisia virgata (Cockerell) (Hemiptera, Pseudococcidae), is a widely distributed and polyphagous pest species, which naturally occurs on cotton plants in Brazil. This study evaluated the establishment and population growth as well as the within-plant distribution of F. virgata on four cotton cultivars: CNPA 7H (white fibers), BRS Verde, BRS Safira, and BRS Rubi (colored fibers). The experiment was conducted in a complete randomized design with four treatments (cultivars) and 18 replications of each. Thus, cotton plants of each cultivar were infested with 100 newly hatched nymphs of F. virgata. The number of adult female mealybugs and the total number of mealybugs per plant were quantified, respectively, at 25 and 50 days after infestation. The developmental and pre-reproductive periods were also determined. Furthermore, we verified the distribution of F. virgata on the plant parts at 25 and 50 days after infestation. Ferrisia virgata showed similar growth of 412-fold in the four cotton cultivars studied. Also, the nymphs were spread on infested leaves; the secondgeneration nymphs were spread and established in all plant parts. Our results characterize F. virgata as having much potential as an important cotton pest in Brazil.

Growth and metabolic activity of the extramatrical mycelium of endomycorrhizal maize plants

The objective of this experiment was to quantify the extramatrical mycelium of the arbuscular mycorrhizal (AM) fungus Glomus etunicatum (Becker & Gerdemann) grown on maize (Zea mays L. var. Piranão) provided with various levels of phosphate fertilizer and harvested at 30, 60 and 90 days after planting (DAP). Total extramatrical mycelium (TEM) was extracted from soil using a modified membrane filtration method, followed by quantification using a grid intersection technique. Active extramatrical mycelium (AEM) proportion was determined using an enzymatic method which measured dehydrogenase activity by following iodonitrotetrazolium reduction. At low levels of added P, there was relatively less TEM than at high levels of added P, but the AEM proportion at low soil P availability was significantly greater than at high soil P.

Peach palm growth and heart-of-palm yield responses to liming

The effects of liming rates on growth and heart-of-palm yield of peach palm plants (Bactris gasipaes Kunth) were studied in a two-year field experiment conducted in Pariquera-Açu, State of Sao Paulo, Brazil. Soils in this region are allic (sub group Ultic Haplorthox), with base saturation ranging from 15 to 26 % of the cation exchange capacity (CEC). A randomized complete block design, with five rates of dolomitic limestone (0, 0.7, 4.7, 8.7, and 14.6 Mg ha-1) and five replications was utilized. Individual plots were composed of 80 plants but only the inner rows (24 plants) were used for data recording. Planting spacing was 2 x 1 m. There was a cubic effect of liming rates on growth and yield. Maximum heart-of-palm yield was estimated to be achieved at 4.3 Mg ha-1 of limestone application, corresponding to 51.4 % soil base saturation. A significant decrease in growth and yield was observed when large amounts of limestone were applied (8.7 and 14.6 Mg ha-1), probably due to a decreased micronutrient availability.

Orchid growth and nutrition in response to mineral and organic fertilizers

Orchid fertilization is fundamental for a satisfactory plant growth and development for commercial orchid production as well as in collections. Mineral and/or organic sources can be used for fertilization. The objective of this study was to evaluate the effect of the use of organic and/or mineral fertilizers on the nutrition and growth of orchid (Laelia purpurata 'werkhanserii' x L. lobata 'Jeni') seedlings in greenhouse. The following fertilizers were tested: an NPK fertilizer + micronutrients; a Ca source in the form of calcium nitrate; two organic fertilizers, one prepared with a mixture of bone meal, castor meal and ash, and a similar commercial fertilizer. The organic fertilizers were distributed on the surface of the pots every two months and the minerals were applied weekly to the substrate in 25 mL aliquots of a solution containing 1 g L-1 of the respective fertilizer. The plant response to the application of mineral together with organic fertilizer was better, with higher dry matter production than by the isolated application of each fertilizer (organic or mineral). The treatments with calcium nitrate + NPK fertilizer did not differ significantly from the use of NPK fertilizer, probably due to the S deficiency detected in a mineral analysis of the tissues. Commercial organic fertilizer had a very elevated B level, leading to toxicity symptoms, reduced growth and necrotized tips of the older leaves in all fertilized treatments.

Aluminum in corn plants: influence on growth and morpho-anatomy of root and leaf

Aluminum (Al) toxicity is one of the most limiting factors for productivity. This research was carried out to assess the influence of Al nutrient solution on plant height, dry weight and morphoanatomical alterations in corn (Zea mays L.) roots and leaves. The experiment was conducted in a greenhouse with five treatments consisting of Al doses (0, 25, 75, 150, and 300 µmol L-1) and six replications. The solutions were constantly aerated, and the pH was initially adjusted to 4.3. The shoot dry matter, root dry matter and plant height decreased significantly with increasing Al concentrations. Compared to the control plants, it was observed that the root growth of corn plants in Al solutions was inhibited, there were fewer lateral roots and the development of the root system reduced. The leaf anatomy of plants grown in solutions containing 75 and 300 µmol L-1 Al differed in few aspects from the control plants. The leaf sheaths of the plants exposed to Al had a uniseriate epidermis coated with a thin cuticle layer, and the cells of both the epidermis and the cortex were less developed. In the vascular bundle, the metaxylem and protoxylem had no secondary walls, and the diameter of both was much smaller than of the control plants.

Seeds with high molybdenum concentration improved growth and nitrogen acquisition of rhizobium-inoculated and nitrogen-fertilized common bean plants

Seeds of common bean (Phaseolus vulgaris) with high molybdenum (Mo) concentration can supply Mo plant demands, but to date no studies have concomitantly evaluated the effects of Mo-enriched seeds on plants inoculated with rhizobia or treated with N fertilizer. This work evaluated the effects of seed Mo on growth and N acquisition of bean plants fertilized either by symbiotic N or mineral N, by measuring the activities of nitrogenase and nitrate reductase and the contribution of biological N2 fixation at different growth stages. Seeds enriched or not with Mo were sown with two N sources (inoculated with rhizobia or fertilized with N), in pots with 10 kg of soil. In experiment 1, an additional treatment consisted of Mo-enriched seeds with Mo applied to the soil. In experiment 2, the contribution of N2 fixation was estimated by 15N isotope dilution. Common bean plants grown from seeds with high Mo concentration flowered one day earlier. Seeds with high Mo concentration increased the leaf area, shoot mass and N accumulation, with both N sources. The absence of effects of Mo application to the soil indicated that Mo contents of Mo-enriched seeds were sufficient for plant growth. Seeds enriched with Mo increased nitrogenase activity at the vegetative stage of inoculated plants, and nitrate reductase activity at late growth stages with both N sources. The contribution of N2 fixation was 17 and 61 % in plants originating from low- or high-Mo seeds, respectively. The results demonstrate the benefits of sowing Mo-enriched seeds on growth and N nutrition of bean plants inoculated with rhizobia or fertilized with mineral N fertilizer.

Effects of nickel and nitrogen soil fertilization on lettuce growth and urease activity

Nickel is a micronutrient involved in nitrogen metabolism and a constituent of the urease molecule. Plant growth and urease activity were evaluated in lettuce (Lactuca sativa L.) grown in soil-filled pots in a 2 x 8 factorial design with two nitrogen (N) sources and eight Ni rates, with five replications. Nitrogen was applied at 200 mg dm-3 (half the dose incorporated into the soil at seedling transplanting and half top-dressed later) using the sources NH4NO3 (AN) and CO(NH2)2 (Ur). The Ni treatments (0, 2, 4, 8, 12, 16, 24 and 32 mg dm-3) were applied as NiCl2. The shoot dry-matter yield, leaf urease activity, Ni levels in the lettuce leaves and Ni levels extracted from soil with Mehlich-3 (M-3) and DTPA were determined. In the plants supplied with AN, the shoot dry-matter yield was higher than in those supplied with Ur. There was no difference in shoot dry matter in response to soil-applied Ni. The leaf urease activity increased with Ni application, regardless of the N source. The extractions with M-3 and DTPA were efficient to evaluate Ni availability for lettuce in the Red-Yellow Latosol.

Soybean root growth and crop yield in reponse to liming at the beginning of a no-tillage system

Analyzing the soil near crop roots may reveal limitations to growth and yield even in a no-tillage system. The purpose of the present study was to relate the chemical and physical properties of soil under a no-tillage system to soybean root growth and plant yield after five years of use of different types of limestone and forms of application. A clayey Oxisol received application of dolomitic and calcitic limestones and their 1:1 combination in two forms: surface application, maintained on the soil surface; and incorporated, applied on the surface and incorporated mechanically. Soil physical properties (resistance to mechanical penetration, soil bulk density and soil aggregation), soil chemical properties (pH, exchangeable cations, H+Al, and cation exchange capacity) and plant parameters (root growth system, soybean grain yield, and oat dry matter production) were evaluated five years after setting up the experiment. Incorporation of lime neutralized exchangeable Al up to a depth of 20 cm without affecting the soil physical properties. The soybean root system reached depths of 40 cm or more with incorporated limestone, increasing grain yield an average of 31 % in relation to surface application, which limited the effect of lime up to a depth of 5 cm and root growth up to 20 cm. It was concluded that incorporation of limestone at the beginning of a no-tillage system ensures a favorable environment for root growth and soybean yield, while this intervention does not show long-term effects on soil physical properties under no-tillage. This suggests that there is resilience in the physical properties evaluated.

Growth and Nutrition of Eucalypt Rooted Cuttings Promoted by Ectomycorrhizal Fungi in Commercial Nurseries

ABSTRACT Ectomycorrhizal fungi (EMF) may improve the adaptation of eucalypts saplings to field conditions and allow more efficient fertilizer use. The effectiveness of EMF inoculum application in promoting fungal colonization, plant growth, nutrient uptake, and the quality of rooted cuttings was evaluated forEucalyptus urophylla under commercial nursery conditions. For inoculated treatments, fertilization of the sapling substrate was reduced by 50 %. The experiment was carried out in a completely randomized design in a 4 × 4 factorial arrangement, wherein the factors were inoculum application rates of 0 (control), 5, 10, and 15 gel beads of calcium alginate containing the vegetative mycelium of Amanita muscaria, Elaphomyces antracinus, Pisolithus microcarpus, andScleroderma areolatum, plus a non-inoculated treatment without fertilization reduction in the substrate (commercial). Ectomycorrhizal fungi increased plant growth and fungal colonization as well as N and K uptake evenly. The best plant growth and fungal colonization were observed for the highest application rate. The greatest growth and fungal colonization and contents of P, N, and K were observed at the 10-bead rate. Plant inoculation with Amanita muscaria, Elaphomyces anthracinus, and Scleroderma areolatum increased P concentrations and contents in a differential manner. The Dickson Quality Index was not affected by the type of fungi or by inoculum application rates. Eucalypt rooted cuttings inoculated with ectomycorrhizal fungi and under half the amount of commercial fertilization had P, N, and K concentrations and contents greater than or equal to those of commercial plants and have high enough quality to be transplanted after 90 days.

Physiological responses of two tropical weeds to shade: I. Growth and biomass allocation

Ipomoea asarifolia (Desr.) Roem. & Schultz (Convolvulaceae) and Stachytarpheta cayennensis (Rich) Vahl. (Verbenaceae), two weeds found in pastures and crop areas in Brazilian Amazonia, were grown in controlled environment cabinets under high (800-1000 µmol m-² s-¹) and low (200-350 µmol m-² s-¹) light regimes during a 40-day period. For both species leaf dry mass and leaf area per total plant dry mass, and leaf area per leaf dry mass were higher for low-light plants, whereas root mass per total plant dry mass was higher for high-light plants. High-light S. cayennensis allocated significantly more biomass to reproductive tissue than low-light plants, suggesting a probably lower ability of this species to maintain itself under shaded conditions. Relative growth rate (RGR) in I. asarifolia was initially higher for high-light grown plants and after 20 days started decreasing, becoming similar to low-light plants at the last two harvests (at 30 and 40 days). In S. cayennensis, RGR was also higher for high-light plants; however, this trend was not significant at the first and last harvest dates (10 and 40 days). These results are discussed in relation to their ecological and weed management implications.

Effect of management practices on mycorrhizal infection, growth and dry matter partitioning in field-grown bean

The experiment was carried out on unsterilized field soil with low phosphorus availability with the objective of examining the effect of cultural practices on mycorrhizal colonization and growth of common bean. The treatments were: three pre-crops (maize, wheat and fallow) followed by three soil management practices ("ploughing", mulching and bare fallow without "ploughing" during the winter months). After the cultural practices, Phaseolus vulgaris cv. Canadian Wonder was grown in this soil. Fallowing and soil disturbance reduced natural soil infectivity. Mycorrhizal infection of the bean roots occurred more rapidly in the recently cropped soil than in the fallow soil. Prior cropping with a strongly mycorrhizal plant (maize) increased infectivity even further.

Growth and yield of common bean cultivars at two soil phosphorus levels under biological nitrogen fixation

The genotypic differences on growth and yield of common bean (Phaseolus vulgaris L.) in response to P supply were evaluated in a field experiment under biological N2 fixation. Eight cultivars were grown at two levels of applied P (12 and 50 kg ha-1 of P -- P1 and P2 respectively), in randomized block design in factorial arrangement. Vegetative biomass was sampled at three ontogenetic stages. The effects of genotype and phosphorus were significant for most traits, but not the genotype ´ phosphorus interaction. The cultivars presented different patterns of biomass production and nutrient accumulation, particularly on root system. At P1, P accumulation persisted after the beginning of pod filling, and P translocation from roots to shoots was lower. The nodule senescence observed after flowering might have reduced N2 fixation during pod filling. The responses of vegetative growth to the higher P supply did not reflect with the same magnitude on yield, which increased only 6% at P2; hence the harvest index was lower at P2. The cultivars with highest yields also presented lower grain P concentrations. A sub-optimal supply of N could have limited the expression of the yield potential of cultivars, reducing the genotypic variability of responses to P levels.

Growth and biomass allocation of the C4 grasses Brachiaria brizantha and B. humidicola under shade

The growth and biomass allocation responses of the tropical forage grasses Brachiaria brizantha cv. Marandu and B. humidicola were compared for plants grown outdoors, in pots, in full sunlight and those shaded to 30% of full sunlight over a 30day period. The objective was to evaluate the acclimation capacity of these species to low light. Both species were able to quickly develop phenotypic adjustments in response to low light. Specific leaf area and leaf area ratio were higher for low-light plants during the entire experimental period. Low-light plants allocated significantly less biomass to root and more to leaf tissue than high-light plants. However, the biomass allocation pattern to culms was different for the two species under low light: it increased in B. brizantha, but decreased in B. humidicola, probably as a reflection of the growth habits of these species. Relative growth rate and tillering were higher in high-light plants. Leaf elongation rate was significantly increased on both species under low light; however, the difference between treatments was higher in B. brizantha. These results are discussed in relation to the pasture management implications.