Cotton Nets Research Articles

Field Tests with Repellent-Treated Netting Against Black Salt-Marsh Mosquitoes13

In 1965 and 1966, 25 single compounds and 6 mixtures were tested as repellents on 4-mesh-per-inch cotton netting against the black salt-marsh mosquito, Aedes taeniorhynchus Wiedemann. Twenty single compounds gave 90% protection for periods ranging from 16 to 92 days. Four of the 6 mixtures gave protection for 19 days. The 3 most effective chemicals were dipentyl tartrate, 92 days; hexyl p-isopropylmandelate, 78 days; and N, N -dibutyl-o-ethoxy-benzamide, 56 days.

A verandah-trap hut for studying the house-frequenting habits of mosquitos and for assessing insecticides. 2. The effect of dichlorvos (DDVP) on egress and mortality of Anopheles gambiae Giles and Mansonia uniformis (Theo.) entering naturally.

Assessment of the effects of dichlorvos (DDVP), released from a Ciba XI dispenser, on females of Anopheles gambiae Giles and Mansonia uniformis (Theo.) entering a verandah-trap hut in the Umbugwe area of Tanzania was made over a period of two months in 1964. Of the numbers of A. gambiae that entered one treated and one untreated hut, 27 per cent, of those entering the hut treated with dichlorvos and 48 per cent, of those entering the untreated hut left again. Of the numbers leaving each hut, 38 per cent, left through the eaves of the treated hut as compared with 9 per cent, in the untreated one. In the case of M. uniformis, 88 per cent, of those entering the treated hut and 94 per cent, of those entering the untreated hut left again. Of the numbers leaving each hut, 59 per cent, left through the eaves of the treated hut as compared with 61 per cent, in the untreated one.Over-all mortalities were 56 per cent, for A. gambiae and 34 per cent, for M. uniformis when the eave-egress fraction from the treated hut was taken into account, compared with 62 per cent, for A. gambiae and 43 per cent, for M. uniformis when the eave-egress fraction was ignored.The results of bioassays and of chemical analyses showed that the problem of mortality from fumigation in situ was considerably less in verandah traps than indoors or in window traps fitted with funnels of cotton netting.

The Relative Efficiency of Nylon and Cotton Gill Nets for Taking Lake Trout in Lake Superior

The change from cotton to nylon twine for gill nets in 1949–52 resulted in a sharp increase in the efficiency of the most important gear used for taking lake trout in Lake Superior, and, consequently, biased estimates of fishing intensity and abundance severely.From early May to the end of September 1961, short gangs (2000 or 4000 linear feet) of cotton and nylon nets were fished in parallel sets for lake trout. A total of 343,000 feet of gill netting was lifted. Nylon nets were 2.25 times as efficient as cotton nets for taking legal-sized fish and 2.8 times as efficient for undersized lake trout. The average lengths of legal, undersized, and all lake trout taken in nets of the two materials did not differ greatly. The percentage of the catch which was undersized (less than 1.25 lb, dressed weight) was 20.8 in nylon nets and 17.7 in cotton. The relative efficiency of cotton and nylon nets showed no trend during the season. The efficiency ratio determined in this study was closely similar to that obtained by earlier workers.Correction of estimates of fishing intensity and abundance for the greater efficiency of the nylon nets used since 1951 has not been attempted. The drastic decline of the lake trout fishery has forced fishermen to make changes in fishing practices in the past few years that cause new bias of an unknown extent to estimates of fishing intensity.

Selectivity and Efficiency of Experimental Gill Nets in South Bay and Georgian Bay of Lake Huron

Gill-net selectivity curves for ciscoes (Coregonus artedii), round whitefish (Prosopium cylindraceum), chub species (mainly Coregonus hoyi, with a few representatives of C. reighardi), yellow perch (Perca flavescens), and white suckers (Catostomus commersoni) were obtained from the analysis of catch statistics of experimental nylon gill nets fished in Georgian Bay in 1958 and 1959 and in South Bay during the period of 1954 to 1959 inclusive. The method for analysis of the data is similar to that developed by McCombie and Fry (1960). The relative efficiency of nylon and cotton gill nets in catching these species has been compared on the basis of catches of each material made in South Bay. Nylon gill net was found to be 1.3 to 3.6 times as effective as cotton, depending on the species. With the exception of yellow perch, the size composition of catches made with nylon and cotton nets does not differ significantly.

Selectivity of Gill Nets for Lake Whitefish, Coregonus clupeaformis

Abstract The methods by which the curve of gill-net selectivity has been determined by various workers are discussed. An empirical demonstration of the applicability of the normal curve of probability to the distribution of size classes of lake whitefish (Coregonus clupeaformis) in catches from experimental gangs of gill nets fished in South Bay, Lake Huron, from 1954 to 1958 is presented. A plot was made of the numbers of fish caught in each length class against the logarithms of the ratios of the girth of the fish to the perimeter of the mesh. An adjustment was made to allow for the presence of unequal numbers of the various length classes in the population fished. The curves for all length classes concerned when superimposed were found to be essentially the same and could be described by the normal frequency distribution with the mode at 0.100 and a standard deviation of ± 0.0514, expressed as logarithms of fish girth to mesh perimeter. The efficiencies of nylon and cotton nets are discussed on the bas...

網地の磨耗

Cotton nets were weared by the rotating drum in water tank as shown in Fig. 1. The coef-ficient of friction was calculated with the records of reading of spring balance S and hanging weight W. Break test on the net pieces were done, the breadth and length of which are 10 meshes respectively, by using the sample in the initial and final stage in our experiment. Where, the time interval of our experiment was 4 hours. The results obtained are as follows:- The value of the coefficient of friction decreases with the increase of the time, and finally it approaches to a certain limiting value (Fig. 2 and Table 1). If the breaking load of the piece of net before and after the treatment of 4 hours be denoted by T0 and T respectively, the value of T/T0 seems to be large in the case of heavy weight and thin cord (Table 1).

綿漁網腐朽に関する粘度的研究

The weakening of cotton netting cords, being immersed in sea water, may be due mainly to bacterial decompositions of cellulose chains. A continuous reduction of average degree of polymerization (??) of the cellulose chains should then be expected to occur with increasing the period of immersion. In this investigation, such reduction of ?? occurring in cotton netting in cotton netting cords immersed in sea water was pursued by measuring intrinsic viscosities of cellulose nitrate om acetone and by comparing them with the tensile strengths of single yarns. It was found that the tensile strengths of single yarns began to decrease after 30 days immersion, reach one half of the initial value after 60 days and dropped to zero after 90 days; on the contrary, the average molecular weights showed slow reduction and reached no more than one half of the initial value for the peirod of 90 days. The linear relationship between the tensile strength and the reciprocal of average degree of polymerization which was often found to fit well for linear high polymers could not be obtained in the present investigation. It is considered that the tensile strength of cotton yarns may be responsible not only for the rupture of primary valence bond and the slippage of the cellulose chains with respect to each other, but also for the more macroscopic structures.

The Production of Fast Shades on Knitted Cotton Fabrics, Nets and Lace*

SummaryMethods of dyeing vat and Soledon dyes on knitted cotton fabrics, nets and lace on the winch machine are described. Means of overcoming frothing and oxidation difficulties with vat dyes are suggested, and a general method for dyeing a selection of the faster‐to‐light Soledon dyes without removal from the winch, based on washing between dyeing and developing, is described.

The Preservation of Fishing Nets, Trawl Twines and Fibre Robes for Use in Sea Water

Manila ropes and trawl twines, and cotton nets, have been immersed in clean sea water for periods up to 14 months, some with alternate wetting and drying, some wet all the time, but in both cases accompanied by storage in air after immersion. All the untreated specimens perished, but the 700 lb. manila ropes retained at least 40% of the original tensile strength.in every case in which a copper soap had been included in the treatment. A previous treatment with cutch is a considerable advantage as shown by the 500 lb. manila ropes and trawl twines, though cutch alone is worthless. Coal tar distillates after cutch are, however, more useful than when used alone, and their mixture with copper soaps gives excellent results. Cutch fixed with bichromate gives tolerably good preservation on nets up to 6 months, but is a poor preservative for trawl twines and ropes which are expected to have a long life. The choice of the copper soap used depends upon the material to be preserved. Naphthenate is the most soluble and penetrates thick ropes excellently; on fine nets it leaches out easily. Oleate is cheaper, but its penetration is less; it does very well with tar on twines and nets. Resinate is the least soluble, but is useful with creosote oil or tar. On account of their greasy nature naphthenate and oleate act as lubricants in ropes.Immersion tests on other preservatives, kindly suggested by Dr S. G. Barker, are to be begun.

The Preservation of Fishing Nets by Treatment with Copper Soaps and Other Substances. Part III

1. Frequent treatment with cutch is injurious, but Olie's method (cutch and ammoniacal copper sulphate) applied every four months preserved cotton netting for six years and eight months in Aquarium sea-water.2. Varieties of cutch tested showed differences which were quite insignificant in comparison with the improvement effected by adopting One's method, which was effective with all on cotton.3. A single treatment by Olie's method preserved trawl twines of Benares sann hemp, New Zealand Phormium fibre and of sisal (E. African) for 34, 34 and more than 48 months respectively under conditions such that the untreated twines perished in less than five months.4. Cotton treated with cutch alone is but little improved by a dip in crude phenols, but a neutral tar oil obtained from the “Coalite” low temperature distillation process was found useful.

The Preservation of Fishing Nets by Treatment with Copper Soaps and Other Substances

1. Under the conditions of the tests cotton and hemp nets became rotten in Aquarium tank water in two months or less in summer, in 4½–5½ months in winter.2. A mixed copper soap, containing oleate, stearate, and palmitate, is as good, probably rather better, than is copper oleate as a net preservative.3. “Cuprinol,” a petroleum acid copper soap, is better than the fatty acid soaps, both in fresh and in salt water. It is more than three times as expensive, however.