Study On Ecological Habit And Flight Range Of Anopheles Sinensis In Yongcheng City, Henan Province, China

Objective (1) To determine the breeding site characteristics of An. sinensis and its related environmental and physicochemical parameters in Yongcheng city by integrated application of field investigation and laboratory test, and to determine whether the breeding habit of An. sinensis has changed or not.(2) To determine the blood sucking habit of An. sinensis by comparing the relative attractiveness of different animal baits versus human bait to An. sinensis.(3) To make a clear understanding of the resting habit of An. sinensis so as to provide scientific evidence for controlling the vector of P. vivx malaria.(4) To study the dispersal range of An. sinensis and provide evidence for the development of effective control measures for malaria elimination in China.Methods (1) Random repeated cross sectional study was undertaken in six villages of Yongcheng city characterized by different levels of the historical incidence of P. vivax malaria. The potential breeding sites of An. sinensis larvae in each village were examined twice per month both in the household courtyards and the village surroundings. The larval sampling was done by the standard dipping method. The anopheline mosquito larvae and emerged adults were identified to the species level by the rDNA PCR technique. Chi-square analysis and Logistic regression analysis were applied to determine the importance of factors for explaining the presence of An. sinensis larvae.(2) Three villages were randomly selected from the six villages mentioned above, and the blood-sucking habit of An. sinensis was studied by integrated application of Latin square design and multiplex PCR method.(3) The resting habit of An. sinensis was investigated by cross sectional study in three villages of Yongcheng city. The"black box" and "manual searching" were used in Zenglou village in2010;"window trap" was used in Renhu village and Chentulou village in2011.(4) The mark-release-recapture technique was conducted in which3000wild^n. sinensis and3000newly emergent An. sinensis were collected and reared in two villages of Yongcheng City in2010and2011, respectively. Marked An. sinensis was daily recaptured for ten successive days using light traps.Results (1) According to the rDNA PCR assay, all sampled anopheline mosquito larvae and emerged adults belonged to An. sinensis. Only three containers sampled from the household courtyards were found to contain An. sinensis larvae. There were no differences in the species composition of mosquito larvae among containers that contained water in the household courtyards (P>0.05). An. sinensis larvae were shown to be present in a total of60breeding sites in the village surroundings; this included8(13.3%) river fringes,26(43.3%) ponds,23(38.3%) puddles, and3(5.0%) irrigation/drainage ditches. Logistic regression analysis revealed that the breeding site type, water depth, chemical oxygen demand (COD), ammonia nitrogen, and sulphate were found to be the key factors determining the presence of An. sinensis larvae. Approximately94.9%of An. sinensis larvae inhabited relatively large and medium-sized water bodies, with depths between0.5m and1.0m (73.3%), COD lower than2mg/L (75%), ammonia nitrogen lower than0.4mg/L (86.7%), and sulphate lower than150mg/L (58.3%), respectively.(2) Culex tritaeniorhynchus was the most prevalent mosquito species and An. sinensis was the sole vector of P. vivax malaria in Yongcheng city. There was significant differences (P<0.01) in the abundance of An. sinensis collected in distinct baited traps. The ranking derived from the mean number of mosquitoes per bait indicated that pigs, goats and calves frequently attracted more mosquitoes than others tested hosts (dogs, humans, and chickens). These trends were similar across all capture nights in three distinct villages. The human blood index (HBI) of female An. sinensis was2.94%when computed with mixed meals.19:00-21:00was the primary peak of host-seeking female An. sinensis while4:00-5:00was the smaller peak at night. There was significant correlation between the density of female An. sinensis and the average relative humidity (P<0.05) in Wangshanzhuang village.(3) In2010, results of "manual searching " and "black box" method demonstrated that cowshed, sheep pen, pig sty were the main resting sites of An. sinensis in the household courtyard; bridge hole, toilet, grass, haystack also found a small amount of An. sinensis and probably the main resting sites in the village surroundings. In2011, based on the results of Chentulou, only five An. sinensis were collected in window trap. In Renhu village,26An. sinensis were collected in window trap, mainly in18:00-19:00(11An. sinensis).(4) The overall recapture rates were0.83%(95%CI,0.50%～1.16%),1.33%(95%CI,0.92%～1.74%) in2010and2011, respectively. Over eighty percent of marked An. sinensis was recaptured within a radius of100m from the release point with a maximum dispersal range of400m. There was no significant differences in the recapture rates (x2=3.499, P>0.05) in different years, but significant differences in dispersal ranges (Fisher’s Exact Test x2=16.237, P＜0.01) and dispersal directions (x2=30.016, P<0.01) in different years.Conclusion (1) These results indicate that the majority of An. sinensis larval breeding sites were relatively large and medium-sized water bodies with depths between0.5m and1.0m, and containing low levels of COD, ammonia nitrogen, and sulphate, respectively. For effective An. sinensis larval control, the type of breeding site, water depth, COD, ammonia nitrogen, and sulphate should be given higher priority over other factors in areas where it is the primary vector.(2) Pigs, goats and calves were more attractive to An. sinensis than dogs, humans, and chickens. Female An. sinensis blood sucking activity mainly occurred from19:00to21:00. Thus, we propose that future vector control against An. sinensis in the areas along the Huang-Huai River of central China should target the interface of human activity with domestic animals and adopt before human hosts go to bed at night.(3) An. sinensis tend to rest in indoor habitats during the study period. The main resting sites in household courtyard were cowshed, sheep pen, and pigsty. Bridge hole, the top of toilet, grass, and haystack are resting places of outdoor circumstances.(4) The present study is the first application of mark-release-recapture method to the study of An. sinensis flight distance. Our results indicate that local An. sinensis had limited flight ranges. Therefore, control efforts should target breeding sites and resting places in proximity of the villages.