Untreated Leaf Research Articles

Evaluation of untreated and urea molasses-treated finger millet (Eleusine coracana) straw and lowland bamboo (Oxytenanthera abyssinica) leaf hay on nutritive values and the performance of Gumuz sheep in Ethiopia.

The experiment was conducted to evaluate effects of untreated and urea molasses-treated finger millet straw and lowland bamboo leaf hay feeding on nutrient utilization, growth and carcass characteristics of Gumuz sheep. Twenty yearling intact male sheep with initial body weight of 21.6 ± 1.31kg (mean ± SD) were purchased from local market and were used for 7- and 90-day digestibility and feeding trials, respectively. The sheep were grouped into five blocks of four animals and randomly assigned to four dietary treatments. The treatment diets were untreated finger millet straw (UFMS) + 150g wheat bran (WB) and noug seed cake (NSC) mixture (T1), untreated lowland bamboo leaf hay (ULBLH) + 150g WB and NSC mixture (T2), urea molasses (UM)-treated finger millet straw (TFMS) + 150g WB and NSC (T3), and UM-treated lowland bamboo leaf hay (TLBLH) + 150g WB and NSC mixture (T4). Water and salt were given freely throughout the experimental period. Data were analyzed using ANOVA procedure of SAS software. The result of the experiment indicated that better CP was recorded in T4 (21.8%) than other treatments. The total DM intake of sheep was significantly (p < 0.001) higher for T2 = T4 > T3 > T1. Significantly higher (p < 0.001) CP intake was recorded in T4 than T3. Similarly, significantly higher CP digestibility was recorded in groups assigned in T4 than other treatments. UM treatment significantly improved (p < 0.05) the FMS than LBL in most of nutrients. Moreover, significantly (p < 0.001) higher ADG was recorded for T2 and T4 than T3; treatment on FMS did not show significant (p > 0.05) effect. T4 and T3 were similar and significantly higher in most of the carcass parameters except in hot carcass weight. In conclusion, UM treatment could be taken as an option to improve nutritive value of locally available lowland bamboo leaf hay and finger millet straw.

Predation on Diamondback Moth Larvae and Aphid by Resistant and Susceptible Lady Beetle, Eriopis connexa.

A successful pest control requires both chemical and biological agents for most commercially grown crops. However, insecticide resistance is increasing worldwide. Cabbage, a widely grown Brassicaceae, hosts the most resistant insect pest to insecticides, the diamondback moth (DBM), Plutella xylostella L. However, insecticide-resistant populations Eriopis connexa (Germar), a lady beetle often found controlling aphids and other soft-bodied pest species sharing brassica fields with DBM. Thus, as a model for integration of insecticide and biological control methods, we evaluated predation by pyrethroid-resistant and pyrethroid-susceptible lady beetles on DBM larvae offered alone and in the presence of a preferred prey, the aphid Lipaphis pseudobrassicae (Davis). During 24-h exposure, resistant and susceptible E. connexa consumed an average of 9.8 and 6.0 second-instar instar DBM larvae, respectively. Resistant beetles showed no significant preferences for prey consumption between untreated and deltamethrin-treated leaf surfaces, at field-recommended rate. As a function of DBM availability, resistant beetles exhibited similar predation on treated and untreated arena and higher predation than susceptible beetles in a treated arena. In greenhouse cages, resistant and susceptible beetles exhibited similar survival after 10days on cabbage treated with deltamethrin and promoted the reduction of DBM to 5.0% and 5.6%, respectively. Both populations fed on a mixed diet of aphids and DBM larvae even under high availability of the preferred aphid prey. Resistant E. connexa survives deltamethrin exposure and do not alter their predatory behavior in response to this insecticide-treated environment.

Experimental Investigation on the Thermal Behavior of Untreated and Alkali-Treated Pineapple Leaf and Coconut Husk Fibers

The primary objective of this research work is to study the thermal behavior of untreated and alkali treated pineapple leaf (PALF) and coconut husk fibers (COIR). In this context, firstly the cellulosic fibers were treated with an alkali solution of various concentration (2%, 4%, 6%, 8%, and 10 wt%) then secondly the change in their surface chemistry and thermal stability were investigated by means of a Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis technique (TGA) respectively. A significant variation in the chemical composition of cellulosic fibers was observed after an alkaline treatment. Changes in the peak at 1745, 1525, and 1250 cm−1 in FTIR spectra corresponds to the partial removal of hemicellulose and lignin components. The thermal degradation of lignocellulosic fibers consists of two major steps i.e. moisture loss (below 150°C) and the decomposition of hemicellulose, cellulose, and lignin components (between 150°C to 400°C). An alkali treatment increases the thermal stability of pineapple leaf and coir fibers through physical and chemical changes. It was observed that the 4 wt% NaOH treated PALF and COIR fibers possess higher thermal stability as compared to other treated and untreated fibers. PALF exhibits a higher rate of decomposition than the COIR fiber but its main decomposition peak lies at a higher temperature of about 40°C.

Fabrication of pandanus tectorius (screw-pine) natural fiber using vacuum resin infusion for polymer composite application

Natural cellulose fiber extract from Pandanus tectorius (Screw pine) leaves is comprehensively investigated as viable alternative for synthetic based fibers made from petro-chemical which is non-degradable and toxic. P. tectorius leaves fiber is extracted and investigated as reinforcement in polymer composite for engineering applications. The habitant are easily found and grown along mangroves and in local jungles located at shallow water. The plant can grow up to 14m tall. In order to use these continuous cellulose fibers as reinforcement in polymer composites, the microstructural analysis and yield content analysis were carried out using SEM micrographs to establish the certainty of using them as reinforcement fiber. The alkaline, bleaching and combined alkaline-bleach treatments are utilized in extraction of the cellulose fiber to evaluate the effect on the mechanical property. The cellulose percentage of the fiber was increased as the concentration and soaking time were increased. The extraction process resulted in 73% cellulose percentage for 10wt. % NaOH and 120min treatment. Hence, it caused 87% increment in cellulose percentage compared to the untreated leaf. The combined alkali-bleach cellulose fiber composite showed 40% higher tensile strength compared to untreated cellulose fiber composite at 35 2.8MPa.

Splitting Tensile Strength, Physical and Durability Properties of Cement Stabilized Earth Block Reinforced with Treated and Untreated Pineapple Leaf Fibre

In the present study, the physical and mechanical strength of cement stabilized earth block reinforced with treated and untreated pineapple leaf fibre (T-PALF, N-PALF) have been studied. Three types of blocks were casted, firstly the block of dimensions 290*140*120mm were casted and these block were casted for abrasion test, secondly the cube blocks of dimensions 150*150*150mm were made and they were casted for water absorption and density test; thirdly were casted cylinder block of dimensions 200*100mm for Splitting tensile strength. It was found that, the water absorption of the blocks increase with increase of fibre content, the density decrease with fibre content. The fibre have increased the abrasion resistance and tensile strength of the blocks up to 3% of fibre content afterward it decreased. It was also observed that, the T-PALF had significantly improved the properties of the blocks comparing to those reinforced with N-PALF.

Leaf disc-mediated oral delivery of small molecules in the absence of surfactant to the two-spotted spider mite, Tetranychus urticae.

The two-spotted spider mite (TSSM), Tetranychus urticae, is a chelicerate herbivore with a wide host range and strong ability to develop pesticide resistance. Experimental TSSM populations are easy to maintain, and the recent publication of the complete TSSM genome sequence and development of RNA interference-based reverse genetics protocols make this species an ideal chelicerate model for the study of pesticide resistance and plant-herbivore interactions. In such studies, treated leaf discs are often used for oral delivery of test compounds. When preparing these leaf discs, the organosilicone surfactant Silwet L-77 is used to promote wetting of the leaf surface and distribution of the test compound across the entire leaf surface. Here, we examined the toxicity of Silwet L-77 and found it to be toxic to TSSMs. We then developed a novel means of preparing leaf discs in which a polypropylene sheet rather than Silwet L-77 was used to ensure distribution of a tracer dye across the entire leaf surface. These leaf discs were then successfully used to deliver the tracer dye into the midgut of TSSMs. No significant differences were observed in the survival, fecundity, or feeding activity of TSSMs fed on leaf discs treated with water via our novel method compared with those fed on untreated leaf discs. Thus, our novel method of preparing leaf discs eliminates concerns regarding the bioactivity of surfactants in TSSMs, and we anticipate that it will be useful for improving oral delivery-based bioassays that use TSSMs.

A simple and inexpensive method for practical storage of field-sample proteins for subsequent MALDI-TOF MS analysis

BackgroundProtein-containing samples can readily be characterised and/or identified using matrix-assisted laser-desorption and ionisation time-of-flight mass spectrometry (MALDI-TOF MS). This technique however requires relatively-fresh biological material that contains proteins that have not yet undergone significant degradation. For field-work collection of samples, problems are often encountered due to delays between collection and sample processing, sample storage (possibly at elevated temperature and/or humidity in some climates), quarantine/regulatory restrictions on the transfer of living biological materials across national borders, and the potential to transfer unwanted microorganisms via non-living biological materials.ResultsIn an attempt to overcome the above difficulties, we have developed a simple and inexpensive method for practical storage of field-sample proteins, for subsequent MALDI-TOF MS analysis, in which biological material is crushed onto filter paper and dried. The dried and protein-impregnated filter paper can then be soaked in an alcoholic solution suitable for the inactivation of microorganisms of concern and again dried for storage. After subsequent dry storage, the proteins may be eluted from the paper using a solution containing acetonitrile, trifluoroacetic acid, water, and MALDI-TOF MS matrix near to saturation. The extracted proteins are then pipetted onto the MALDI-TOF MS sample plate for subsequent analysis. Using this method, spectra of comparable quality to fresh-material controls have been obtained for acid-soluble proteins from Fallopia japonica and Impatiens glandulifera leaf material. Unlike untreated leaf material, high-quality spectra can be obtained with and without alcohol treatment even after storage for one month at up to 40 °C.ConclusionsWe have developed a simple and inexpensive method for practical storage of field-sample proteins for subsequent MALDI-TOF MS analysis. Key benefits of this approach are a reduction in sample degradation, and consequent conservation of taxon-discriminatory spectral profiles, whilst minimising the potential for carryover of viable microorganisms.

Chemical composition and repellent activity of essential oils from the leaves of Cinnamomum zeylanicum and Eugenia uniflora against Diaphania hyalinata L. (Lepidoptera: Crambidae)

Diaphania hyalinata is an important pest in organic melon crops and has caused considerable harm to growers in northeastern Brazil. The aim of the present study was to determine the chemical composition of essential oils from Eugenia uniflora (pitanga) and Cinnamomum zeylanicum (cinnamon) as well as evaluate the repellant action, oviposition deterrence and effect on body mass caused by the oils and the constituents linalool and β-pinene in D. hyalinata. The essential oils from pitanga and cinnamon had a predominance of sesquiterpenes and phenylpropanoids, respectively. The pitanga oil was more effective as a larval repellent than the cinnamon oil and the constituents tested exhibited low repellent activity. In the evaluation of oviposition deterrence, the response of D. hyalinata exposed to the cinnamon oil did not vary with the distance between the treated and untreated leaf disks, but varied significantly when exposed to the pitanga oil. Linalool exhibited greater long-distance oviposition deterrence in comparison with β-pinene. In the experiments on body mass gain, second-instar larvae were more susceptible to the cinnamon oil than the pitanga oil and constituents tested. The findings suggest that these oils, especially the pitanga oil, could be an alternative for the control of D. hyalinata in the larval and adult phases. Further studies are needed to evaluate the effect on natural enemies and pollinating insects as well as the cost–benefit of the formulation of an insecticide for use on organic crops in northeastern Brazil.

Establishment of Metarhizium anisopliae (Metchnikoff) sorokin as endophyte in maize and sorghum

Glasshouse experiments were conducted to establish an indigenous soil-derived strain of Metarhizium anisopliae (ICAR-NBAIR Ma-35) as endophyte in maize and sorghum by artificial inoculation through foliar spray of conidial suspension. Colonization of M. anisopliae were studied at 15, 30, 45, 60, 75 and 90 Days After Treatment (DAT) in stem and leaf tissues of maize and sorghum by plating technique and PCR method. Metarhizium anisopliae showed variation with regard to the extent of colonization in stem and leaf tissues of maize and sorghum. In maize, colonization was observed at 30DAT in stem and 30-45DAT in leaf. In sorghum, colonization of M. anisopliae was observed during 15-60DAT in stem and 15-75DAT in leaf indicating longer persistence compared to maize. Colonization of M. anisopliae was observed in young growing stem tips and leaves (unsprayed) indicating the internal spread of M. anisopliae in maize and sorghum plants. M. anisopliae was not detected in the untreated stem and leaf tissues of maize and sorghum. The positive results of colonization of M. anisopliae in maize and sorghum stem/leaf tissues observed in plating technique were confirmed by the PCR amplification.

Effect of Fiber Loadings and Treatment on Dynamic Mechanical, Thermal and Flammability Properties of Pineapple Leaf Fiber and Kenaf Phenolic Composites

This study deals with the analysis of dynamic mechanical, thermal and flammability properties of treated and untreated pineapple leaf fiber (PALF) and kenaf fiber (KF) phenolic composites. Results indicated that storage modulus was decreased for all composites with increases in temperature and pattern of slopes for all composites, having almost the same values of E' at glass transition temperature (Tg). The peak of the loss modulus of pure phenolic composites was shown to be much less. After the addition of kenaf/PALF, peaks were higher and shifted towards a high temperature. The Tan delta peak height was low for pure phenolic composites and maximum for 60% PALF phenolic composites. Cole-Cole analysis was carried out to understand the phase behavior of the composite samples. Thermogravimetric analysis (TGA) results indicated that pure phenolic composites have better thermal stability than PALF and kenaf phenolic composites. Vertical and horizontal UL-94 tests were conducted and showed pure phenolic resin is highly fire resistant. The overall results showed that treated KF composites enhanced the dynamic mechanical and thermal properties among all PALF/KF composites.

Biological Activity of Serine Protease Inhibitor Isolated from the Seeds of Phaseolus vulgaris

Seed flour extract of local common bean cultivar Baspa inhibited gut proteases of Spodoptera litura Fab. The inhibitor protein was purified by ammonium sulphate precipitation and gel filtration chromatography. Freshly laid eggs of Pieris brassicae L. treated with 220-µg inhibitor protein showed 89.60% reduction and delay in hatching by 2 days as compared to control. Feeding neonate larvae of P. brassicae on cabbage leaf discs coated with inhibitor protein (79.25 and 118.88 µg) for 6 days resulted in 50 and 89% larval mortality and reduction in larval growth by 20.77 and 48.47% as compared to untreated control. The treated larvae (118.88 µg) shifted on untreated leaf discs showed mortality after 3 days. However, the growth of treated larvae (79.25 µg) fed on untreated leaf discs further decreased to 45.17% showed delayed pupation, deformed pupa formation and no adult emergence in contrast to control larvae.

Ultrastructures of Colletotrichum orbiculare in Cucumber Leaves Expressing Systemic Acquired Resistance Mediated by Chlorella fusca.

Chlorella, one single-cell green algae organism that lives autotrophically by photosynthesis, can directly suppress some plant diseases. The objective of this study was to determine whether pre-spraying with Chlorella fusca suspension could induce systemic acquired resistance (SAR) in cucumber plants against anthracnose caused by Colletotrichum orbiculare. In order to illustrate SAR induced by algae, infection structures in host cells were observed under a transmission electron microscope (TEM). Cytological changes as defense responses of host mesophyll cells such as accumulation of vesicles, formation of sheath around penetration hyphae, and thickness of cell wells adjoining with intracellular hyphae were demonstrated in cucumber leaves. Similar defense responses were also found in the plant pre-treated with DL-3-aminobutyric acid, another SAR priming agent. Images showed that defense response of host cells was scarcely observed in untreated leaf tissues. These cytological observations suggest that C. fusca could induce SAR against anthracnose in cucumber plants by activating defense responses of host cells.

The Tensile Strength Evaluation of Untreated Agel Leaf/Jute/Glass Fiber-Reinforced Hybrid Composite

The aim of this study is to obtain and compare the tensile strength of untreated agel leaf/jute/glass fiber-reinforced hybrid composites. Six types of composite specimens are fabricated using hand-layup followed by vacuum bagging method. Unsaturated polyester is used as matrix and fibers are not chemically treated. Each type of specimens is reinforced using 7 plies of fibers with different stacking sequences. Pure untreated agel leaf fiber-reinforced composite is used as control variable. All specimens are tensile tested under ASTM D638 condition. The results show that pure untreated agel leaf fiber-reinforced composite has the lowest value of tensile strength. Agel leaf/jute fiber-reinforced composite has bigger tensile strength than pure agel leaf fiber-reinforced composite. Incorporating glass fiber can enhance the value of tensile strength significantly and this value is proportional to the quantity of glass fiber its self.

Modulation of δ-aminolevulinic acid dehydratase activity by the sorbitol-induced osmotic stress in maize leaf segments

Osmotic stress induced with 1 M sorbitol inhibited δ-aminolevulinic acid dehydratase (ALAD) and aminolevulinic acid (ALA) synthesizing activities in etiolated maize leaf segments during greening; the ALAD activity was inhibited to a greater extent than the ALA synthesis. When the leaves were exposed to light, the ALAD activity increased for the first 8 h, followed by a decrease observed at 16 and 24 h in both sorbitol-treated and untreated leaf tissues. The maximum inhibition of the enzyme activity was observed in the leaf segments incubated with sorbitol for 4 to 8 h. Glutamate increased the ALAD activity in the in vitro enzymatic preparations obtained from the sorbitol-treated leaf segments; sorbitol inhibited the ALAD activity in the preparations from both sorbitol-treated and untreated leaves. It was suggested that sorbitol-induced osmotic stress inhibits the enzyme activity by affecting the ALAD induction during greening and regulating the ALAD steady-state level of ALAD in leaf cells. The protective effect of glutamate on ALAD in the preparations from the sorbitol-treated leaves might be due to its stimulatory effect on the enzyme.

Characterization and Analysis of Extraction Process-parameter of Pandanus tectorius (Screw-pine) Natural Fiber for Polymer Composites

Natural cellulose fiber extract from Pandanus tectorius (Screw pine) leaves is comprehensively investigated as viable alternative for synthetic based fibers made from petro-chemical which is non-degradable and toxic. Pandanus tectorius leaves fiber is extracted and investigated as reinforcement in polymer composite for engineering applications. The habitant are easily found and grown along mangroves and in local jungles located at shallow water. The plant can grow up to 14 meters tall. In order to use these continuous cellulose fibers as reinforcement in polymer composites, the microstructural analysis and yield content analysis were carried out using SEM micrographs to establish the certainty of using them as reinforcement fiber. The alkaline, bleaching and combined alkaline-bleach treatment is utilized in extraction of the cellulose fiber to evaluate the effect on the mechanical property. The cellulose percentage of the fiber was increased as the concentration and soaking time were increased. The extraction process resulted in 73% cellulose percentage for 10 wt.% NaOH and 120 minutes treatment. Hence, it caused 87% increment in cellulose percentage compared to the untreated leaf.

Acaricidal activity and sublethal effects of the microbial pesticide spinosad on Tetranychus urticae (Acari: Tetranychidae)

Laboratory bioassays were conducted to evaluate the toxicity of the microbial pesticide spinosad to different life stages of the two-spotted spider mite, Tetranychus urticae Koch, as well as its sublethal effects on reproduction and population growth of this important mite pest. The biopesticide was applied to bean primary leaves or leaf discs carrying spider mites using a Potter spray tower (2.7 mg/cm2 aqueous deposit). The following LC50 and LC90 (mg/L) estimates for motile stages were obtained in acute toxicity bioassays: 27.52 and 116.72 (larvae), 36.55 and 136.20 (protonymphs), 82.76 and 721.28 (female deutonymphs), and 61.47 and 457.21 (adult females). Spinosad showed no significant ovicidal action: toxic effect observed after spraying eggs (LC50 = 105.78 mg/L, LC90 = 596.95 mg/L) was the result of its residual action on larvae that hatched from the treated eggs. The effects of spinosad on life history traits and population growth of adult female survivors from treatments with 240, 120 and 60 mg/L were evaluated in two successive 7-day bioassays on untreated leaf discs. In the first bioassay, females that survived treatments as 24 h old eggs and completed their juvenile development on treated leaves had significantly lower gross fecundity, net fecundity and instantaneous rate of increase (ri) but the reduction was merely 4–6%, 9–11%, and 2–3%, respectively. Female longevity was significantly reduced (approximately by half a day) only after treatment with 240 mg/L. In the second bioassay, in which females were treated during their pre-ovipositional period, the treatments with 240 and 120 mg/L significantly reduced their gross fecundity (16–17%), net fecundity (28–31%), ri values (8–9%) and female longevity (approximately by one day). Spinosad effects on the intrinsic rate of increase (rm) and other demographic parameters were evaluated in two successive bioassays in which life tables were constructed for females that survived treatment with 120 mg/L at the egg stage (first demographic bioassay) or pre-ovipositional period (second demographic bioassay). In the first bioassay, the intrinsic rate of increase was significantly higher in treated (rm = 0.278) than control mites (rm = 0.267) as a result of higher net fertility at the beginning of reproduction of treated females. In the second bioassay, treated females had significantly lower rm than control females (0.254 and 0.283, respectively). The results obtained in this study indicate that spinosad, applied against insect pests (at field relevant rates of 60–240 mg/L), could eliminate a part of T. urticae population as well, but survivors would retain a significant potential for population recovery.

In vivo label-free mapping of the effect of a photosystem II inhibiting herbicide in plants using chlorophyll fluorescence lifetime

BackgroundIn order to better understand and improve the mode of action of agrochemicals, it is useful to be able to visualize their uptake and distribution in vivo, non-invasively and, ideally, in the field. Here we explore the potential of plant autofluorescence (specifically chlorophyll fluorescence) to provide a readout of herbicide action across the scales utilising multiphoton-excited fluorescence lifetime imaging, wide-field single-photon excited fluorescence lifetime imaging and single point fluorescence lifetime measurements via a fibre-optic probe.ResultsOur studies indicate that changes in chlorophyll fluorescence lifetime can be utilised as an indirect readout of a photosystem II inhibiting herbicide activity in living plant leaves at three different scales: cellular (~μm), single point (~1 mm2) and macroscopic (~8 × 6 mm2 of a leaf). Multiphoton excited fluorescence lifetime imaging of Triticum aestivum leaves indicated that there is an increase in the spatially averaged chlorophyll fluorescence lifetime of leaves treated with Flagon EC—a photosystem II inhibiting herbicide. The untreated leaf exhibited an average lifetime of 560 ± 30 ps while the leaf imaged 2 h post treatment exhibited an increased lifetime of 2000 ± 440 ps in different fields of view. The results from in vivo wide-field single-photon excited fluorescence lifetime imaging excited at 440 nm indicated an increase in chlorophyll fluorescence lifetime from 521 ps in an untreated leaf to 1000 ps, just 3 min after treating the same leaf with Flagon EC, and to 2150 ps after 27 min. In vivo single point fluorescence lifetime measurements demonstrated a similar increase in chlorophyll fluorescence lifetime. Untreated leaf presented a fluorescence lifetime of 435 ps in the 440 nm excited chlorophyll channel, CH4 (620–710 nm). In the first 5 min after treatment, mean fluorescence lifetime is observed to have increased to 1 ns and then to 1.3 ns after 60 min. For all these in vivo plant autofluorescence lifetime measurements, the plants were not dark-adapted.ConclusionsWe demonstrate that the local impact of a photosystem II herbicide on living plant leaves can be conveniently mapped in space and time via changes in autofluorescence lifetime, which we attribute to changes in chlorophyll fluorescence. Using portable fibre-optic probe instrumentation originally designed for label-free biomedical applications, this capability could be deployed outside the laboratory for monitoring the distribution of herbicides in growing plants.

Effect of pesticides on microorganisms involved in litter decomposition in cacao plantation in Ile-Ife, Nigeria

Wide spread use of pesticides by farmers in agro-ecosystems to control pests may cause the disruption of nutrient cycling by adversely affecting the organisms especially microorganisms, namely bacteria and fungi, involved in decomposition processes thus altering normal nutrient cycling pattern in these ecosystems. This study, therefore, identified and determined the dynamics of bacterial and fungal species involved in cacao leaf litter decomposition and the effect of the pesticide, Ridomil Gold 66WP on the species. This was with a view to understanding the effects of pesticides used to control pests and diseases on litter decomposition rate in cacao plantations. Cacao leaf litter decomposition was studied using litterbag method. Freshly fallen leaf litter was thoroughly mixed and divided into two groups, treated and untreated. The treated was sprayed with Ridomil Gold 66WP at the rate of the recommended field rate of 3.3 g/L and air dried. 20 g of treated and untreated litter were weighed, put in separate 15 cm × 15 cm of 1.0 mm mesh size litter bags and randomly placed on the floor of cacao plantations in Ile-Ife, Nigeria. Three litter bags of each group were randomly retrieved from the plantation on monthly intervals for each month and the content of each litterbag was weighed to determine the rate of decomposition of the litter. The litter contents of each group litter were bulked, ground and microbiological analyses carried out to isolate, characterise and identify the species of bacteria and fungi involved in cacao leaf litter decomposition. The rate of decomposition of pesticide treated cacao leaf litter (0.473) was lower than that of untreated litter (0.582). A total of 31 microbial species consisting of 13 bacterial species and 18 fungal species were isolated from decomposing cacao leaf litter during the sampling period. More fungal species (16) than bacterial species (9) were involved in untreated cacao leaf litter decomposition. Species of the genera Klebsiella, Pseudomonas, Aspergillus, Penicillium and Rhizopus were the most common microorganisms involved in decomposition of cacao leaf litter. Ridomil Gold 66WP did not have significant effect on the total heterotrophic bacterial and fungal counts throughout the sampling period though their counts in treated litter were lower than in untreated litter. There were also no significant monthly variations in both total bacterial and fungal counts. It was concluded that the pesticide, Ridomil Gold 66WP, though had adverse effect on the rate of decomposition of cacao leaf litter, it did not have any adverse effect on the species of bacteria and fungi involved in decomposition of cacao leaf litter.

Relative toxicity of insecticides to the crucifer pests Plutella xylostella and Myzus persicae and their natural enemies

The widespread and intensive use of conventional pesticides, particularly insecticides, presents a major risk to natural enemies of target pests, as well as to the environment in general. The aim of this study was to investigate the differential intrinsic toxicity of insecticides to two key pests of crucifers, Plutella xylostella and Myzus persicae and their respective hymenopteran parasitoids, Cotesia vestalis and Aphidius colemani. Such knowledge can help inform effective integration of insecticides and biological control in IPM systems. Three insecticides generally regarded as being compatible with natural enemies (abamectin, spinosad and indoxacarb) and one compound regarded as harmful to natural enemies (lambda-cyhalothrin) were examined. A comparative measure of the intrinsic toxicity of fresh deposits of insecticides on Chinese cabbage leaf discs was determined for both pest and parasitoids species after exposure to insecticide for 24 h and 120 h, and after 24 h exposure to insecticide plus 96 h on untreated leaf discs. Differences in the susceptibility of pests and parasitoids to different insecticides were marked for P. xylostella and C. vestalis, LC50 values being significantly lower for the pest species. Such differences were not observed for M. persicae and A. colemani. There was a direct relationship between dose, exposure time and toxicity for all insecticides tested. All insecticides tested showed lower toxicity to both parasitoids compared with P. xylostella, which suggests that for this pest species side-effects on parasitoids can be minimised through IPM practices that reduce exposure time to such non-target organisms.

Host Phenology and Leaf Effects on Susceptibility of California Bay Laurel to Phytophthora ramorum.

Spread of the plant pathogen Phytophthora ramorum, causal agent of the forest disease sudden oak death, is driven by a few competent hosts that support spore production from foliar lesions. The relationship between traits of a principal foliar host, California bay laurel (Umbellularia californica), and susceptibility to P. ramorum infection were investigated with multiple P. ramorum isolates and leaves collected from multiple trees in leaf-droplet assays. We examined whether susceptibility varies with season, leaf age, or inoculum position. Bay laurel susceptibility was highest during spring and summer and lowest in winter. Older leaves (>1 year) were more susceptible than younger ones (8 to 11 months). Susceptibility was greater at leaf tips and edges than the middle of the leaf. Leaf surfaces wiped with 70% ethanol were more susceptible to P. ramorum infection than untreated leaf surfaces. Our results indicate that seasonal changes in susceptibility of U. californica significantly influence P. ramorum infection levels. Thus, in addition to environmental variables such as temperature and moisture, variability in host plant susceptibility contributes to disease establishment of P. ramorum.