| BackgroundsThe flies can carry many kinds of pathogens, and spread many kinds of diseases. According to the statistics, it can spread dozens of serious diseases, such as cholera, typhoid fever, dysentery, the tuberculosis and so on. The larva of the flies can also directly enter each part of bodies of human and livestock, and cause myiasis, which is harmful to human. The density and extinguishing situation of flies can directly reflect the civilized hygienic degree of some region, therefore massive insecticides have been widely used in each place along with the launching of the patriotic health campaign. However, it led to flies' increasing of resistance to commonly used insecticide in each place, and rose year by year. Therefore, it is urgent to find out the situation, take countermeasure to depress and postpone the flies' insecticide resistance to insecticide and reduce the environment pollution caused by the chemistry insecticide.Shaoxing urban district is located north Zhejiang plain, the east longitude 120 degree, the north latitude 30 degree, year to year climate temperate is moist. With the densely population, it is developed in restaurant industry, and its nature, humanities and geographic condition are extremely suitable for flies to perch and reproduction. Along with the urban construction development and the change of life style and the behavior of the people, taking powerful measures to extinguish the flies in the campain of constructing national health city, and the warming change of climate in recent years, tremendous changes have taken place in flies species reproduction and breed environment compared with the past, which caused the change of flies'population distribution and rule of seasonal variation. At present, there is rare systemic study on flies in Shaoxing. Therefore, this investigation of flies from 2003 to 2004 in Shaoxing urban district was carried out, to find out the flies' population distribution, seasonal variation and housefly's insecticide resistance and its density and relation with intestinal infectious disease, and to provide scientific reference for the control of flies and the prevention of intestinal infectious disease .MethodsInvestigation spots were established in new urban district and old one respectively in Shaoxing city. Each investigation spot was composed of waste transfer site, inhabited area, agricultural market fair, restaurant industry, greenbelt and so on. It had 5 kinds of habitat, total 11 surveillance spots. The cage-fly-trap method was used to survey the flies every ten day and identified species of captured flies. Topical application was used to determine the houseflies' insecticide resistance nature to 6 kinds of chemical insecticide such as dichlorvos (DDVP) etc. The intestinal infectious disease epidemic material was acquired from infectious disease epidemic statistics report in YueCheng CDC.Round distribution method was used to carry on the analysis of flies' seasonal variation, while linear regression analysis method were applied to analyze the relation between intestinal infectious disease morbidity and flies' density and temperature, and weighted linear regression method to compute houseflies' insecticide resistance LD50.The data reorganization as well as all statistical analysis were processed and completed in Excel 2003 and SPSS13.0.Results1. Species population distributes and the seasonal variation of flies in Shaoxing urban districtAfter classified and identified, in Shaoxing urban district flies could be divided into 5 families 10 genuses,16 species, in which Chrysomyia megacephala, Musca domestica, Lucilia sericata the housefly were dominant species, and ALdrichina grahami, Lucilia illustris, Sarcophaga peregrine, Musca sorbens, Cryptolucilia caesarion ,Muscina stabulans were common species, others were rare species.Species number, sequence of composition and density of flies varied in differentyear and different investigation spot. Species population density of investigation spot in new city was significantly higher than in old one. And the average density of flies in 2004 was higher than that in 2003.The flies' species composition and density varied in different habitat. The average densities of flies in breed and move and inhabit place of greenbelt was the highest in two years, reached 320.38 per cage per day, and the second was agricultural market fair, 187.91 per cage per day. Waste transfer site and inhabited area were basically close, 127.58 per cage per day and 127.44 per cage per day respectively. The restaurant industry was the lowest, 116.14 per cage per day. The density of Chrysomyia was the highest in each place.The flies' seasonal variation showed obvious seasonal characteristic. In Shaoxing urban district, from 2003 to 2004 the flies' average density peak date was on Aug. 4, the peak time interval was from June 8 to Sep. 30; on Aug. 11, from June 17 to Oct. 5 in 2003; on July 29, from June 1 to Sep. 26 in 2004.2. The influence of ambient temperature to seasonal variationThrough regression analysis the relation between flies' average density of each month and average temperature of each month, the research indicated that temperature and flies' density presented correlation dependence. When temperature rose, fly density increased along with, which prompted that we should adjust fly control strategy and reasonably arrange the flies killing work according to the situation of the year temperature change and fly density variation.3. Relation between flies' density and intestinal infectious diseaseMusca class density was an important factor which affected the morbidity of intestinal infectious disease. Through correlation analysis the relation between the morbidity of intestinal infectious disease and seasonal variation of flies' density in two years, the research showed that in 2003 and 2004 the correlation coefficient r of the flies' density and the morbidity of intestinal infectious disease were 0.846 and 0.612 respectively, which demonstrated the flies' density was an important influence factor of incidence of intestinal infectious disease.4. Insecticide resistance of houseflyIn Shaoxing urban district housefly presented different insecticide resistancelevel to Decamethrim, Beta-cypermethrin, Permethrin, Tetramethrin, Dichlorvos(DDVP) , Fendona(alphacypermethrin). And it had achieved the maximum resistantlevel to DDVP and Decamethrim, and higher anti-level to Permethrin ,and lower anti-level to Tetramethrin. Compared with the CDC of Zhejiang Province 1981-1983 examination data, the determination result of Shaoxing urban district showed that the insecticide resistance of housefly to Decamethrim grew most quickly and during 23 years grew 50 times, next, the insecticide resistance of housefly to Fendona(alphacypermethrin), grew 32 times, and above 10 times to Dichlorvos (DDVP) and Tetramethrin.ConclusionsFrom this research, we can draw the conclusion: In Shaoxing urban district species population distribution of flies is different with other areas. Different month and different habitat could cause different species population composition and different density. The flies' seasonal fluctuation presents obvious seasonal characteristic. The relation between environment temperature and flies' density shows correlation dependence, and the flies' density increases in certain scope along with the temperature rises. The flies' density is an important factor to influence the morbidity of intestinal infectious disease. While the former rises, the latter increases. In Shaoxing urban district, housefly has very high level of insecticide resistance to Dichlorvos, Decamethrim, Alphacypermethrin , which develop relatively slow to Dichlorvos and Permithrin, and implementation of comprehensive treatment and reasonable use of insecticide may suppress and delay the resistance development.
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