| For the phenomenon that chironomid breed on a large-scale in Baota district of Yan'an,and adults swarming seriously affect residents'outing activities.In October,November,2016,and May and June of 2017,the chironomid adults of swarming were screened and sampled.Taking the distribution range and quantity as the criterion of selecting the dominant species,the dominant species of chironomid in Baota district of Yan'an were determined.The surface water quality of Baota district of Yan'an was preliminarily assessed by using the species distribution of adults.On this basis,the experimental population of dominant species was established,combined with the results of field surveys,the biological characteristics of dominant species and the annual life history in Baota district were studied.In addition,the dynamic life table of the experimental populations of dominant species was constructed and analyzed,which is of great significance for exploring the causes of the large number of chironomid and how to prevent and control them ecologically.The main findings are as follows:A total of 2 subfamily 10 genera of chironomid adult were collected in t Baota district of Yan'an,which belong to Rheopelopia,Trissopelopia,Macropelopia,Procladius,Tanypus of Tanypodinae and Polypedilum,Chironomus,Microchironomus,Paratendipes,Glyptotendipes of Chironominae.Among them,Tanypus punctipennis of Tanypus is the dominant species in Baota district of Yan'an,which distributes most widely and accounts for more than 90%of the survey results.Using the species distribution of chironomid adult as indicator species,a preliminary assessment of surface water quality in Baota district of Yan'an was carried out.The mass propagation of Tanypus punctipennis,which shows that the surface water environment in Baota district belongs to the moderate degree of pollution,and the increasingly eutrophic water quality environment provides a good basic condition for the large-scale breeding of chironomid.Tanypus punctipennis a completely metamorphosis,the larval period can be divided into four instars.After the third instar,the larvae have the corresponding morphological structure to maintain their genus and species.The eggs are long oval,brownish yellow,and multiple eggs are encased in the egg membrane to form a spherical structure.The larvae are long cylindrical worms,the length of the head of the larvae is about 2 times the width of the head,the antenna can be freely extended into the antenna sheath.the length of the procercus are generally about 5 times than width,with a highly developed anterior parapods and posterior parapods.The pupa period was significantly shorter than the larval period,the characteristics deepened,did not eat,the swimming speed became slower,the pupa period was shorter,and the gender can be judged initially by body width at the pupa period.In addition to body width,the biggest difference in shape between male and female chironomid is antenna.Male antenna long,dense distribution of multiple fluffy wheel hairs,far from the feather shape,and female antenna are moniliform with distinct segmentations and only a small amount of bristles scattered on the base.In terms of life habits,larvae are predatory,and larval period does not nest,From the second instar,they enter sediment,preferring clay soil.Adults must lay eggs after mating.Marriage flying places are often chosen in areas close to water sources and rich in vegetation.Adults must lay eggs after swarming and mating,swarming places are often located in areas close to water sources and rich in vegetation.Tanypus punctipennis occur in the Yan'an area for two generations a year.The generations do not overlap.When the temperature is higher than 20°C,the larvae develop pupae.In winter,the mature larvae overwinter,the peak period of Tanypus punctipennis activity is from May to October.The larval period of Tanypus punctipennis can obviously be divided into four ages by head shell width,the range of the width of the head shell of each age was calculated.The first instar larvae:98.92±8.33 um,the second instar larvae:193.33±16.67 um,the third instar larvae and the fourth instar larvae were 321.69±24.07 um and 470.43±32.36um.In the dynamic life table of the experimental population of Tanypus punctipennis,which was formed at the day age as a time interval,the whole generation experienced about 49.45±2.14 d,and the average developmental duration of the larval period was the longest,including the shortest first instar period and the longest in the fourth instar,which were 1.05±0.50 d and 15.62±1.05 d.The egg period and the pupa period were relatively short,which were 1.91±0.82 d and 1.58±0.74 d,the adult period is second,for3.45±2.14 d.In the dynamic life table of the experimental population of Tanypus punctipennis,which was formed at the insect age as a time interval.In the adult period,a total of 2 egg pieces were collected,counting 821 eggs,the average surviving individual has a spawning number of 22.81.The fecundity mx of the experimental population was 22.81,and the net reproduction rate of the population was R0=2.31>1.The population gradually became larger,the next generation population was 2.31 times of the current generation,the instrinsic growth rate of the population was rm=0.02>0,and the intrinsic growth rate of the population was positive,indicating that the experimental population of the Tanypus punctipenni has a tendency to grow under the condition that the feeding conditions are not changed.By comparing the population survival of different instars,it was found that the killing power of larvae and eggs was higher,and the killing power of the first-instar larvae was the highest.The survival curve of the population is concave curve,the mortality rate of larvae is higher,but the survival rate to the third and fourth age is lower,which requires higher birth rate to compensate.In the selection of reproductive strategies,r-selection is more preferred,with more and smaller offspring,adopting a once lifetime or explosive reproductive mode. |
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