| Seabuckthorn is playing a special important role in the ecological construction in Three North area. In recent years, the leaf-eating pest Trabala vishnou gigantina Yang has broken out in Wuqi county of Shaanxi, and has seriously affected the ecological stability of seabuckthorn plantations. There are few scientific researches being published on this moth in China or abroad. The bio-ecology, sex attractant effect, host selection behavior, and two color morph phenomenon of the larvae have been investigated for the first time in this research, which would provide a scientific basis for integrated management. The main results and conclusions are as follows:(1) The research results of biological characteristics through field survey and laboratory breeding and observation indicated that a generation takes one year in Wuqi of Shaanxi. The eggs were found to overwinter on cocoon、branch and litter. Eggs begin to hatch in the mid or late May. Larvae begin to pupate in late July, with the average pupal stage lasting24.5±3.1d. Adults emerge from late August to late September, with the peak of eclosion in early September. The longevity of adults is6-13days. Female adults start oviposition on2d after the emergence, and the average fecundity is about297per female.(2) The spatial distribution of larvae of T.vishnou gigantina were analyzed using the aggregation indices and the regression model. The results showed that the spatial pattern of larvae was aggregation distribution. The basic componernt of distribution was individual colony. The aggregation increased generally with the increasing density. The reason for aggregatied may be its bionomics and other environmental factors. Based on the distribution pattern, the optimal sampling number and sequential sampling table were calculated.(3) The developmental period, developmental threshold temperature and effective accumulated temperature of different life stages of T.vishnou gigantina were determined in the laboratory. The results indicated that the developmental periods of life stages decreased in length with increasing temperature. The developmental threshold temperature of eggs, larvae and pupae were9.24±0.45,10.85±0.87and14.56±0.85respectively, and their effective accumulative temperatures were341.22±9.54,1285.64±17.65and445.35±8.65degree day respectively. The numbers of larval instars were determined using coefficient of variation and Crosby ratio through field sample. Larval stage comprised seven instars and the head capsule width was the best instar-dividing structure. Three variables including distance between simple eyes, cranial width and mandible width could be used for the separation of larval instars for the sclerotized structures.(4) The eclosion, mating and oviposition were studied through field survey and laboratory breeding and observation. The results showed that the emergence period of the pest lasted for40days. The daily emergence peak occurred from17:00to23:00, and counted82.46%to the number of daily emergence. The ratio of female to male was1:1.41. The lifespan of the unmated female and male were averagely11.05days and9.85days respectively, whereas that of the copulated female and male were8.05days and7.35days on average respectively, indicating that mating shorten the lifespan of male. In the field tests, the highest percentage of the male moths was trapped during3:00-5:00, and more males were trapped by2-day-old virgin female moths than by female moths of other ages. The mating rate on the second night was the highest (45.6%) and then decreased gradually. The mating peak took place from3:00to4:00. Females normally copulated only once in their whole life span, with several times for males. For most of the adults, the duration of mating was14～16hours. Approximately82.40%of eggs were laid during night time. The unmated female could lay eggs, but those unfertilized eggs couldn’t hatch. The emergence activity, the mating activity and the oviposition activity were synchronized at different ages and time of the scotophase.(5) Results of the feeding and oviposition preference of T. vishnou gigantina showed that the feeding amount on H. rhamnoides were the biggest while just a few moths emerged from Prunus armeniaca. No moth was found on other plant species in the field. The feeding preference tests in the laboratory showed that the moths could feed on all plant species, and young larvae had more stronger selective than old ones. Results of the field survey indicated that the amount of eggs on different species ranked as:cocoon shell> H.rhamnoides> Robinia pseudoacacia> Caragana Korshinskii> weeds. The oviposition preference tests in the laboratory showed that the number of eggs on H.rhamnoides was the maximum, and the minimum was on Populus davidiana.(6) The differentiation of the larval color morph of T. vishnou gigantina was studied through laboratory breeding and observation. The results showed that the larvae had a distinct two color morph phenomenon, but there was no larval sexual dimorphism. The larvae began to differentiate into white morph and yellow morph at the4th instar. Color of the white morph larvae kept white and unchanged, while yellow morph larvae changed to white after molting, and then graded gradually from white to yellow in three or four days. The white morph larvae had the characteristics of greater food consumption, faster body growth and stronger reproductive capacity, while yellow morph larvae had the characteristics of higher survival rate and stronger starvation resistance. In a certain range, numbers of white morph larvae increased with the increasing of temperature and population density. It was not related with humidity and light. |
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