| Chironomids are important aquatic insects, with complete metamorphosis, and the benthic larval stages are distributed in various water. The larvae are diets for fish with high nutritional value, and not easy to pollute the water. Now, it has been the development of large-scale farming, and as a commodity to as some rare ornamental fish food organisms on the market.At present, the large-scale cultivation of chironomid larvae are in nature, easy to get the influence of the temperature, high winds, hail and other natural weather. Chironomus kiiensis Tokunaga is the dominant species in Guangdong province. In this paper, the developmental duration of different stages of Chironomus kiiensis were studied, then the developmental threshold temperature and effective accumulated temperature were calculated. In order to further the occurrence regularily of Chironomus kiiiensis, and to provide scientific basis for the forcast, actual production of the insect in Guangzhou province and the low temperature are to keep the larvae alive. In addition, with the rapid development of chironomid morphology, the morphology of the research method is becoming more and more efficient, so in this paper, the larval instars and stadia of Chironomus dorsalis Anderson were determined, in order to distinguish and judge the larva of the best morphological characteristic and indicators, which has certain significance for the classification and identification of larvae as well as populations age, but also provides an effective method for the later research of orther types of larval instar. To this end, we begin to study the chironomid, mainly include the following aspects:1. Identification of Chironomid speciesAt present, the most common way is to collecte larvae in the field, saved and lead back to the laboratory for identification according to the traditional method. The author collected a midge in a chironomid breeding field in Huizhou City of Guangdong Province at 2013 November,which was identified as Chironomus kiiensis Tokunaga; In 2014 June, the author collected a midga in an aquaculture farm in the coastal town of Pudong New Area in Shanghai, which was identified as Chironomus dorsalis Anderson. Taking the two chironomid larvae as experimental materiais to carry out the following research.2. Determination of larval lnstars and stadia of Chironomus dorsalis AndersonThe most widely used structures in identification of larval instars is the size that ventral view, head capsule width and length. In addition to these two common measurement indexes, this paper also studied the other six morphological index, which was also used to determine the age and the number of the larvae of Chironomus dorsalis. The number of larval instars and stadia of each instar of the Chironomus dorsalis(Diptera: Chiromomidae) were determined by artificial rearing and sampling periodically. The head capsule length, length between top of the median teeth of mentum and leading coronoid, head capsule width, mentum width, median teeth width of mentum, antenna length, antennal basipodite length, antennal ratio(the ratio between antennal basipodite length and the length of rest sections) were examined for choosing the optimal morphological characterristics or index to distinguish the larval instars. According to the frequency distribution, deviation analysis and regression analysis, results show that the larvae of Chironomus dorsalis have 4 instars. The antenna length can be the best characteristic and variable for the distinguishment of larval instars, and the second was the length between top of the median teeth of mentum and leading coronoid, and mentum width. The average stadia of 1-4 based on the method of median population were 1.32 d, 2.00 d, 7.51 d and 8.39 d, respectively. The total larval stage duration was 19.22 d.3. Study on the developmental durations of different stages of ChironomuskiinensisIn this study, developmental durations of different stages of Chironomus kiinensis Tokunaga(Huizhou) were studied in the laboratary under the conditions of a range of constant temperatures(16, 20, 24, 28, 32 ℃)、75±5 % RH and a photoperiod of L: D=14: 10(Light: Dark). Developmental threshold temperature and effective accumulative temperature were calculated with linear models. The results showed that Chironomus kiinensis Tokunaga could grow normally within a range of 16-32℃, the ralationship between developmental durations, developmental rate and temperatures were significantly related. The developmental threshold temperatures for egg, larvae, pupa, adult and whole generation were 6.5±0.41 ℃, 0.4±0.82 ℃, 14.4±0.47 ℃, 9.4±0.76 ℃, 3.6±1.04 ℃, respectively. The effective accumulative temperatures for egg, larvae, pupa, adult and whole generation were 8.1±1.17d·℃, 289.9±0.10d·℃, 6.3±6.01d·℃, 51.0±1.04d·℃, 371.2±0.08d·℃, respectively. According to the effective accumulative temperature law, we predict that this pest will have about 19 generations annually in Huizhou. |
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