Occurrence and Population Dynamics of Chironomids in Early-Season Rice Fields

The chironomid is one of the world wide distributed insects and normally occurs in a great abundance among many kinds of water bodies. Currently, our knowledge about the chironomid in rice fields is limited to the species survey, and it is considered as a group insect at the family level, termed as a kind of the neutral insects. By using the specially designed emergence traps, the species richness and the occurrence of the chironomid in rice fields were studied throughout the early season in Fuyang City, Zhejiang Province, China. There were four species, namely, Tanytarsus formosanus, Chironomus sinicus, Polypedilum nubifer and Tanypus punctipennis of chironomids collected from rice fields. All of them are widely distributed species. T. formosanus and C. sinicus were the most dominant species in rice fields. The succession of chironomids in the early season could be divided into two phases, the early and the late phases. The abundance of the chironomid was higher in the early phase than that in the late phase. It was estimated that there were around 3 million individuals of chironomids emerged from 667 m(2) rice field throughout the early season. It was also found that the sex ratio of T. formosanus was female-biased during the early phase, whereas male-biased during the late phase. In contrast, the sex ratio of C. sinicus was male-biased throughout the early season.