White Nets Research Articles

Biofouling of fish-cage netting: the efficacy of a silicone coating and the effect of netting colour

The efficacy of a silicone coating (Veridian 2000) to reduce fouling on salmon-cage netting was examined at a salmon farm in Tasmania, Australia. Significantly less fouling occurred on the white silicone-coated netting (1.9 kg/m 2) compared to uncoated white (7.8 kg/m 2) and black (8.5 kg/m 2) netting after 163 days immersion. On silicone-coated netting the green alga Ulva rigida dominated the fouling mass, with smaller amounts of solitary ascidians. In contrast, solitary ascidians dominated the uncoated black and white netting and accounted for more than 75% of the fouling mass. Netting colour significantly affected the growth and composition of algal fouling, but had no effect on invertebrate fouling. Cleaning experiments demonstrated that fouling organisms were poorly adhered to the silicone coating and that relatively little effort was required for their removal. Silicone coatings may provide an effective non-toxic solution to reduce fouling on sea-cages and to increase the ease of fouling removal.

Diel variation in catches of Euphausia superba Dana 1854 early larvae: vertical migration or avoidance reaction?

Samples were obtained with two pairs of black and white nets towed simultaneously at varying light conditions in the Weddell–Scotia confluence region. The statistical analysis (ANOVA, Regression and Kruskal–Wallis test) of the log transformed counts of Euphausia superba calyptopes larvae (CI, CII and CIII) shows that the significant difference between the white and black nets found in daytime are not present in darkness. A negative regression coefficient was detected between the difference in catches and sun's height, pointing to a light dependent avoidance reaction. These results demonstrate that the day/night differences in observed densities of krill larvae are due to net avoidance rather than to vertical migration, a result confirmed by hydroacoustical observations; and that the habitat of these stages is restricted at all times to the upper layers of the ocean.

The Distance from Home: The Domestication of Desire in Interior Design Manuals

In the Beacon Hill interior design showroom, sturdy and elegant pieces of furniture, tantalizingly grouped together, model a room within a home. Old books, baskets of bread and home magazines appoint the simulated living space like props on a stage. Next to an over-stuffed primitive print couch, I pick up the copy of Architectural Digest resting on a coffee table. On the cover, David Bowie stands in front of his Indonesian-style home located on the island of Mustique. Ten glossy pages of magazine photographs seize a nineteenth-century spirit of exoticism in Bowie's refuge; outside his house, Bowie, dressed in a sarong and woven hat, embraces his wife Iman, the Somalian model; inside, Bowie stands by the gilt Balinese-style living-room doors; the master bedroom displays a collection of nineteenth-century Egyptian revival furniture, and the guest bedroom shot reveals twin beds with a palm frond pattern silk screened onto the mosquito netting and the bed coverings. Surely this is the room where I would stay if David Bowie invited me to his home. The white mosquito netting flutters slightly as a cool breeze drifts through the french door. Exhausted from the Caribbean sun, I crawl under crisp cool sheets and take a nap until I am summoned for dinner.

Root respiration rate before and just after clear‐felling in a mature, deciduous, broad‐leaved forest

AbstractSoil respiration was measured throughout the year (June 1992 to May 1993) in a mature, deciduous, broad‐leaved forest and an adjacent, clear‐felled stand which was made in November 1991, in Hiroshima Prefecture, west Japan. The same soil temperature and soil moisture content as those in the forest stand were maintained in two frame boxes covered with sheets of white netting in the clear‐felled stand to observe soil respiration. A herbicide was applied to the cut end of all stumps in one of the two frame boxes in order to kill the root system. There was no significant difference in the aboveground biomass and soil environmental conditions between the forest and the frame boxes in the clear‐felled stands. The difference in soil respiration rate between the forest and the frame box, in which the root system was killed by the herbicide, was considered to be due largely to the contribution of root respiration. Taking into consideration CO2 evolution due to the decomposition of roots killed and the change in A0 layer respiration rate after clear‐felling, the proportion of root respiration to the total soil respiration before clear‐felling was estimated to be 51% annually, which coincides closely with those values estimated previously in mature forests by other methods. The difference in the soil respiration rate between the two frame boxes (one with killed roots and the other with undisturbed roots) suggested that the annual root respiration rate just after clear‐felling dropped to about two‐thirds (70%) of that before clear‐felling.

Introducing insecticide impregnated bednets in an area of low bednet usage: an exploratory study in north-east Ghana.

To find out the acceptability of the use of insecticide impregnated bednets before launching a large-scale trial to evaluate their impact on child mortality, 96 permethrin impregnated bednets were distributed in 4 communities within the Kassena Nankana district of the Upper East Region of Ghana, where previously only 4% of the people had owned a mosquito net. The nets were readily accepted and used by the recipients. The major benefit perceived by the users was the reduction of the nuisance effect of mosquitoes and other insects. The people in the study area normally sleep on mats in either an open courtyard or a sleeping room depending on the weather but this did not deter them from using the nets. The white nets distributed for this study became dirty with use, and users thought they needed to be washed. In order to discourage this, it is recommended that dark coloured nets be used in the main intervention trial. After having used the nets for a year, the community members expressed willingness to buy the nets if they were made available after the harvest season when they had sold their crops and had enough money to pay for them. The results of this study have been used to plan and conduct a large intervention trial.

Use of netting and whitewash spray to protect papaya plants against Nivun Haamir (NH)-dieback disease

A disease causing the decline of papaya ( Carica papaya) plants was noticed in the Jordan Valley in 1982. The disease caused severe yellowing of the upper leaves and dieback of the apex. The disease was not transmissible mechanically and continued efforts to associate viruses and viroids have so far been unsuccessful. Epidemiological observations suggested that the disease is airborne and probably caused by a mollicute. In order to test this hypothesis, plots were covered by an insect-proof net and with white nets providing 15, 30 and 50% shade. The 30%, 50% and insect-proof nettings provided complete protection, and the 15% netting reduced disease incidence to <2%, compared with >37% in the uncovered control plot. Spraying plants at weekly intervals with a commercial whitewash solution was also found to be effective in reducing disease incidence. The advantages of using a range of netting field treatments as a simple means for obtaining information on the epidemiological nature of a new disease are described.

Laboratory colonization of the tsetse fly Glossina pallidipes Austen (Diptera: Glossinidae) using an in vitro feeding method

AbstractAttempts to establish a laboratory colony of Glossina pallidipes Austen from adults and puparia of Uganda origin (Lugala) sent from a colony previously established in Amsterdam have been highly successful. Flies are maintained at 25 ± 0·5°C, L:D 12:12 and 85% RH. They are fed six days per week on whole defibrinated pig blood collected aseptically and irradiated at 1·5 kGy before storage at 4°C. The blood is presented through silicon rubber membranes at 37°C. Virgin female flies are mated when 7–9 days old with equal numbers of 9–12-day-old males in a 30 × 30 × 10-cm cage covered with white Terylene netting and illuminated with a fluorescent light from above, providing 300–500 lux on the cage bottom. The sexes are left together for 40–48 h, during which time they are offered food twice. After separation of the sexes, 30 females are housed in a cage 15 cm in diameter and two males are added. Flies are kept for 90 days before discarding. The establishment of this colony is discussed in terms of the mating behaviour of the species, highlighting differences in the laboratory between G. pallidipes from Uganda and Zimbabwe and between G. pallidipes and G. morsitans morsitans Westwood.

Association of the Boxelder Bug (Hemiptera: Rhopalidae) with Epicarp Lesion of Pistachio Fruits

The boxelder bug, Leptocoris trivittatus (Say), produced epicarp lesions (EL) on developing pistachio ( Pistacia vera L.) fruits. In all caged fruit clusters in the field and laboratory, boxelder bug feeding for 48-72 h caused doughnutlike, water-soaked, brown necrotic lesions. Internally, in immature fruits (April to early May), a white netting or web pattern appeared on the inner shell tissue. As shells hardened (late May), the symptoms appeared as small black spots where bugs fed. Aprotruding elicoidal microscopic stylet sheath or “spike” was sometimes found in the center of the black spots. Boxelder bugs incited EL during the growing season until early June, while the pericarp firmness was ≤1.8kg force.

The quality of seed tubers multiplied in the Golan Heights for the spring season in Israel

Seed tubers grown in the northern mountain region — the Golan Heights — were as productive as imported seed tubers. In cvs. Blanka and Desiree, both the locally grown and the imported seed tubers were similar when yield components and tuber fresh weight are considered. In Up-to-Date, the locally grown seeds produced higher yields of marketable tubers (over 60 g/tuber) than those imported. Desiree seed tubers grown for two generations in the Golan Heights did not differ significantly in their productivity as compared with common Golan seeds and with imported ones. Seed tubers harvested from plots which were protected by means of white coarse nets and weekly sprays with insecticides, were virtually virus-free and were used for growing commercial seeds in the Golan. The use of this method for seed multiplication is suggested.

Reducing the spread of aphid-transmitted viruses in peppers by coarse-net cover

Spread of the aphid-transmitted cucumber mosaic virus (CMV) and potato virus Y (PVY) in pepper plots was markedly reduced by growing the plants under a white coarse-net cover permitting normal development of the plants. This net also reduced the winged aphid population on the plants by more than 40 times. Light grey and yellow nets also reduced virus spread and aphid populations, but were much less effective than white ones. The nets do not act as a mechanical barrier to aphids. It is suggested that under white and grey netting, aphid repellency and microclimatic conditions are the primary causes of virus check, while the controlling effect of the yellow nets may be explained by their being more attractive to aphids than the plants. A reduction of “background effect” and a limiting of the aphids’ vision range by nets are probably other factors involved in the protective mechanism.

Control of non-persistently transmitted aphid-borne viruses

Transmission of non-persistent viruses, characterizedinter alia by acquisition and inoculation of virus during brief probes, absence of a latent period after acquisition, and loss of virus after short feeding periods, has not been reduced satisfactorily by vector control using insecticides. Breeding for resistance is one of the most efficient ways for control, but progress in breeding programs is slow, and resistance depending on one gene only is often overcome by new strains of the virus. Avoidance of infection, and the use of oil sprays, reflective surfaces, yellow sticky traps, white nets and border crops, are reviewed, as possible alternative control approaches. Of these, oil sprays are presently used in practice. The possible mechanisms of the mode of action of oils are discussed. It is expected that these methods, singly or in combination, may become of further importance, especially in highvalue crops such as virus-tested propagation material of flower bulbs and corms.

Effects of Color, Mesh Size, Fishing in Seasonal Concentrations, and Baiting on Catch Rates of Fishes in Gill Nets

Abstract Increasing efficiency of gear to catch more fish per unit of effort and to catch species and sizes selectively are inherent objectives in fishery research, population control, and commercial fishing. Color and mesh sizes of gill nets, fishing in seasonal concentrations of fishes, and baiting gill nets were tested to identify single and combined factors which enhance efficiency of nets for a variety of objectives in Elephant Butte Lake, New Mexico. Catch rates of one to five species of game, forage, and commercial fishes were significantly different (P < 0.10) in nets of any of nine colors than they were in white nets. Seasonal differences occurred between multifilament and monofilament nets. Stretch-meshes ranging from 5.1 to 15.2 cm were selective for all species and the three groups of fishes. Selectivity changed linearly in 10.2-, 12.7-, and 15.2-cm meshes; catches of commercial fish increased and those of game and forage fishes decreased with increasing mesh size. Concentrations of several sp...

Variations in Catchability of Fishes with Color of Gillnets

Abstract Gillnets of nine colors were compared with white nylon to determine effects of each color on catch rates of numbers and weights of 15 species of fishes in Elephant Butte Lake. Data were analyzed with mixed-model analysis of variance. Significantly different catch rates were compared, as fractions of unity (ratios), with rates in white nets. All colors afforded positive or negative selectivity for various species. Seasonal differences in catch rates between colored and white nets were found only in clear monofilament nets. Catch rates in monofilament nets were higher than in white nets during summer when water transparency was low. Catch rates in white nets were higher from September through March when water was relatively clear and monofilament nylon appeared to break light into a spectrum. Most significant differences consisted of reduced catches in colored nets. Thus, use of colors allows selection of species along with handling smaller numbers of unwanted fish. Brown nets caught more catostomi...