Breeding Site Characterization of Anopheles Sinensis Larvae in Chinese Villages

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Characterizing the breeding site of Anopheles sinensis is of major importance for the transition from malaria control to elimination in China. However, little information is available especially regarding the characteristics and influencing factors of breeding sites of An. sinensis in Yongcheng City, a representative region of unstable malaria transmission in the Huang-Huai River region of central China.

The aims of this study were to determine the breeding site characteristics of An. sinensis and related environmental and physicochemical parameters, to find out which breeding site characteristics could best explain the presence of An. sinensis larvae, and to determine whether the breeding habit of An. sinensis has changed or not.

Methods

Random repeated cross sectional study was undertaken in six villages of the 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. Some important breeding site characterizations were recorded and characterized. The anopheline mosquito larvae and emerged adults were identified to the species level morphologically and to sub-species by the ribosomal DNA PCR technique. Chi-square analysis and logistic regression analysis were applied to determine the importance of factors for explaining the presence or absence of An. sinensis larvae.

Results

According to the ribosomal DNA PCR assay, all sampled anopheline mosquito larvae and emerged adults belonged to An. sinensis. Only 3 containers that were 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 of 60 breeding sites in the village surroundings, this included 8 (13.3%) river fringes, 26 (43.3%) ponds, 23 (38.3%) puddles, and 3 (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. Approximately 94.9% of An. sinensis larvae inhabited relatively large and medium-sized water bodies, with depths between 0.5 m and 1.0 m (73.3%), COD lower than 2 mg/L (75%), ammonia nitrogen lower than 0.4 mg/L (86.7%), and sulphate lower than 150 mg/L (58.3%), respectively.

Conclusion

These results indicate that the majority of An. sinensis larval breeding sites were relatively large and medium-sized water bodies with depths between 0.5 m and 1.0 m, 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.

Authors: Xiao-Bo Liu, Qi-Yong Liu, Yu-Hong Guo, Jing-Yi Jiang, Dong-Sheng Ren, Guang-Chao Zhou, Can-Jun Zheng, Jing-Li Liu, Yun Chen, Hong-Sheng Li, Hua-Zhong Li and Qun Li

Full Article: Random repeated cross sectional study on breeding site characterization of Anopheles sinensis larvae in distinct villages of Yongcheng City, People’s Republic of China (PDF)

Source: Parasites & Vectors 2012, 5:58 doi:10.1186/1756-3305-5-58

Published: 23 March 2012

Copyright: © 2012 Xiao-Bo Liu et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

 

Characteristics of Adult Mosquitoes

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QUESTION:

What are the characteristics of adult anophelines and culicines?

ANSWER:

I am assuming your question relates to how adult anopheline and culicine mosquitoes can be differentiated from each other. There are a number of main characters that can be used for identification to genus level, namely in the resting position of the body (and the resultant angle of the proboscis to the ground), the pattern and colour of the wing veins and the relative length of the palps (these are sensory organs located on either side of the proboscis).

Specifically, adult anophelines tend to rest with their bodies at an angle to the ground (head down, body up), whereas culicines tend to rest roughly parallel to the ground. The colouration of the wing veins of anophelines is usually arranged in “blocks” of pale and dark scales, whereas culicines tend to have all-dark scales, or a scattered mixture of pale and dark scales. Finally, if you compare the adult females (all female mosquitoes have non-plumed antennae which contrast very obviously with the males’ plumed antennae, allowing the sexes to be easily differentiated), the palps of the female anophelines are almost as long as the proboscis, whereas they are relatively much shorter in culicines. Both sets of males have palps almost as long as the proboscis, but the tips are swollen in male anophelines whereas male culicines are not, but may have some distal hairs.