Properties and inhibition of insect integumental chitin synthetase

Chitin polymerization is catalyzed by cell-free enzyme complexes from the integument of Trichoplusia ni larvae and wing tissue of developing Hyalophora cecropia pupae obtained on extraction of homogenates for 16 hr at 5°C in 25 mM Tris-HCl buffer, pH 7.2, containing 10 mM MgCl₂, 1 mM dithiothreitol, 10 mg/ml bovine serum albumin, and 4 mg/ml digitonin. In contrast, integumental preparations from Boarmia selenaria, Earias insulana, Heliothis virescens, Oncopeltus fasciatus, Spodoptera exigua, and Tribolium castaneum exhibit little or no chitin synthetase (CS) activity. H. cecropia CS requires magnesium ions but not N-acetyl-d-glucosamine for normal activity and is almost insensitive to nikkomycin and polyoxin D. CS activity is not detected in diapausing H. cecropia pupae but synthesis of this enzyme is induced or its activity is stimulated by the molting hormone, ecdysterone, indicating possible hormonal control. T. ni CS requires magnesium ions and N-acetyl-d-glucosamine for optimal activity and is sensitive to inhibition by uridine di- and triphosphates, polyoxins B and D, and particularly nikkomycin. T. ni integumental CS activity decreases in starved larvae or those about to pupate. Both T. ni and H. cecropia CS enzymes as prepared and assayed are sensitive to captan but not to the potent insecticides diflubenzuron and BAY SIR 8514, two effective benzoylphenyl urea in vivo chitin synthesis inhibitors.     

Using the Tabor Atomizer System to maintain weight and firmness in stored potato tubers

A new fogger — the Tabor Atomizer System — features unique atomizers, based on compressed air and water. The droplets produced have a very small mass (less than 10m,) and behave like a dry cloud, producing 96%–98% relative humidity (RH) without depositing free water on the tubers. After 6 months of storage at 10 C, with 96%–98% RH applied with the Tabor Atomizer System (room A), 92%–94% applied with a spin-disk humidifier (room B), and 82%–86% with no added humidity (room C), the weight losses for stored potatoes were 2%, 7%, and 12%, respectively. The firmness of the tubers expressed as newtons (N) required to penetrate the tubers before storage and after 6 months in room A, B, or C was 76, 74, 68, or 63 N, respectively.     

Prevalence and significant geospatial clusters of bovine tuberculosis infection at livestock–wildlife interface ecosystem in Eastern Tanzania

Bovine tuberculosis (BTB) is an important neglected zoonosis that affects livestock, wildlife and human. A study to determine prevalence and geospatial clusters for BTB was conducted from June 2010 to March 2012 at livestock–wildlife interface areas (LWIA). A total of 1,288 cattle located in vicinity of Mikumi-Selous ecosystem Tanzania were tested. Single Intradermal Comparative Tuberculin Test and spatial scan statistic analysis were applied to establish the status of the disease and identify significant spatial BTB clusters. Overall individual prevalence was 3.7 % (n?=?1,288) (95 % CI?=?2.8–4.9) and 7.8 % (95 % CI?=?6.4–9.4) with cut-off of >4 and >2 mm, respectively. Villages with at least one reactor were 55.8 % (n?=?43). Reactivity was significantly higher in Mvomero and Kilosa districts compared with Kilombero and Ulanga districts (χ ²?=?15.9; P?<?0.001). Significant spatial BTB clusters were revealed at 11 villages. BTB clustering was significant in Kilosa and Mvomero districts compared with Kilombero and Ulanga districts. There was overlap and aggregation of BTB clusters covering south and south-east of Kilosa district bordering Mikumi National Park (MNP) and Mvomero. Generally, clustering occurred around major rivers. The current study provides useful information on the dynamics and epidemiological status of BTB around the wildlife–livestock–human interface, it reveals that the wildlife are at risk of BTB from infected livestock. The study revealed hotspots for BTB that can be applied to guide implementation of participatory intervention at LWIA and control strategies in marginalised pastoralist communities. This study calls for similar studies in other Tanzania’s LWIA for efficient intervention of BTB countrywide.     

Properties of Tribolium gut chitin synthetase

An insect chitin synthetase (CS) is readily assayed using the microsomal fraction (～0.5 mg protein) from an homogenate of Tribolium castaneum larvae. This enzyme preparation is incubated at 22°C with uridine 5′-diphospho-N-acetyl[³H]glucosamine in 355 μl of 25 mM Tris-HCl buffer containing 10 mM MgCl₂, 17 mM N-acetylglucosamine, and 1 mM dithiothreitol. Other divalent cations and amino sugars are less effective activators or are inhibitory. T. castaneum CS is strongly inhibited by polyoxin D and uridine 5′-diphosphate. These activation and inhibition properties of Tribolium castaneum gut CS are similar to those of fungal CS. The polymerization product formed by the Tribolium enzyme is stable in alkali but hydrolyzed by chitinase. Enzymes of Tribolium confusum, Tribolium brevicornis, Tenebrio molitor, and Galleria mellonella are also active under the same conditions. These enzymes are from the gut and probably from the peritrophic membrane. Integumental CS activity is not detected under the indicated assay conditions.     

Response of pepper and eggplant to continuous light in relation to leaf chlorosis and activities of antioxidative enzymes

Activities of the oxygen radical-scavenging enzymes were determined in leaves of ‘Kyomidori’ pepper (Capsicum annuum L.) and ‘Senryo’ eggplant (Solanum melongena L.) seedlings under two photoperiod treatments; 12 h light/12 h dark (12/12 h) or with continuous light (24/0 h) for six days. Growing eggplant under continuous light resulted in leaf chlorosis after four days and a sharp decline in the chlorophyll content. In eggplants grown under 24/0 h photoperiod, the activities of antioxidative enzymes; superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) rapidly increased from day two. This was an indication of photooxidative damage. In contrast, leaf chlorosis did not occur in pepper plants grown under continuous light, while the chlorophyll content was even higher in the 24/0 h than in the 12/12 h photoperiod. Continuous light did not enhance the activities of SOD and POD in leaves of pepper. However, the CAT activity increased faster and was significantly higher in pepper than in eggplants grown under continuous illumination. Pepper plants did not appear to suffer from photooxidative damage and thus grew normally under continuous illumination.     

Eggplant dry matter composition fruit yield and quality as affected by phosphate and total salinity caused by potassium fertilizers in the irrigation solution

Eggplant (Solanum melongena L.) grown under winter conditions in unheated polyethylene covered greenhouse displays unmarketable red color fruit skin. The purpose of this work was to study the effect of potassium (K), phosphate and total salinity levels in the irrigation solution on the quality of eggplant fruit grown at winter and spring seasons. Eggplant was grown in containers filled with basalt erupted tuff scoria. The fertigation solutions were composed of three levels of P: 18, 36, and 54 g P m^‐3, using mono K phosphate (MKP). Each level of P was applied on two levels of total K concentrations, 475 and 920 g K m^‐3 composed of K nitrate, MKP, and K chloride (KCl). The KNO₃ fertilizer was used in all treatments at 150 g N m^‐3. Increasing the KCl concentration increased the average electrical conductivity (EC) in the irrigation solution from 2.3 to 3.9 dS m^‐1, reduced class A fruit number and weight, but had no effect on the skin color. During the cold winter period the intensity of the skin color was weaker than in the normal hot growing period. Increasing the average phosphorus (P) concentration in the irrigation solution throughout the growing season from 36 to 54 g m^‐3 increased the number of fruit per plant, the number of class A fruits but has no significant effect on total fruit yield. Increasing the total electrical conductivity of the nutrient solutions by K fertilizers above 3.8 dS m^‐1 decreased fruit yield and total dry matter in the spring growth period.     

Variation in quantity and quality of native forages and grazing behavior of cattle and goats in Tanzania

The study was conducted to assess the effects of seasonal variation in the quality and quantity of pasture and management of livestock exclosures (ngitili) on the grazing behavior of cattle and goats. The study was 2×2×2 factorial design with three independent variables: season (Dry or Rainy), ngitili management (Private or Communal) and animal species (Cattle or Goats). Focal and scan observation methods were used to record different behavioral activities. Vegetation attributes from the study areas were measured in two consecutive seasons. Most key forage species had significant higher crude protein (CP) content and in vitro organic matter digestibility (INVOMD) in rainy than in dry season (P<0.05), but Neutral Detergent Fiber (NDF) and Acid Detergent Fiber (ADF) did not vary significantly with season (P>0.05). ADF and NDF were significantly higher in species from communal ngitili than those from private ngitili (P<0.05). Above-ground herbaceous biomass and bulk density (BD) were significantly higher in the rainy season and in the private ngitili than in the dry season and in the communal ngitili respectively. Cattle and goats spent considerably more time grazing and browsing respectively in the rainy season than in the dry season (P<0.05). Cattle foraging activities did not vary significantly (P>0.05) with ngitili management, but goats found to spend considerably more time browsing in the communal ngitili and more time grazing in the private ngitili (P<0.05). Despite the merits of stocking cattle and goats together in the heterogeneous pasture, seasonal variation in forage resources requires investigation of other strategies such as use of multipurpose trees and treatment of crop residues to improve livestock production.     

Cytotoxic activity of Ozoroa insignis from Zimbabwe

The crude methanol bark extract of the Zimbabwean medicinal plant, Ozoroa insignis, showed in-vitro cytotoxic activity against Hep-G2 (human hepatocellular carcinoma), MDA-MB-231 (human mammary adenocarcinoma), and 5637 (human primary bladder carcinoma). Bioactivity-directed chromatographic separation led to isolation of anacardic acid and ginkgoic acid as the cytotoxic components.     

Formulation of vegetable fat pellets with pheromone and Beauveria bassiana to control the larger grain borer,Prostephanus truncatus (Horn)

The use of hydrogenated rapeseed oil as a carrier for conidia of the entomopathogenic fungus Beauveria bassiana (Bals) Vuill was investigated as part of a research programme on the control of the larger grain borer, Prostephanus truncatus (Horn). Melting the oil, which is solid at temperatures below 32 °C, allows the incorporation of materials such as aggregation pheromones and conidia; sudden cooling produces solid fat pellets. In attraction tests conducted with pellets containing P truncatus aggregation pheromone, significantly higher numbers of beetles were attracted to pellets containing pheromone at a concentration of 4 ml litre⁻¹ compared to control pellets for at least four weeks when held in Petri dishes in the laboratory and for at least six weeks when pellets held in insect traps were exposed to outside conditions. The attraction was retained over a period of storage in glass bottles; pellets stored in the freezer or incubator (at −10 °C or 27 °C) attracted beetles according to the pheromone level for the duration of the work (14 and 13 months respectively). When pheromones and conidia were incorporated into the same pellets they could be stored in a freezer or refrigerator retaining over 80% viability after 51 weeks; those stored in an incubator at 27 °C showed significantly lower germination at 20.7–27.2% after the same time. There was an indication that the pheromone caused a slight reduction in the viability of conidia, although this may have been just a slight delay in the speed of germination. Rapid dose transfer from pellets with conidia with and without the addition of pheromone was demonstrated. Insects were exposed to pellets for 24 hours and 96–100% mortality was observed in treatments containing conidia within six days of exposure. © 1999 Society of Chemical Industry