Study On The Biological And Ecological Characteristics Of Megastigmus Likiangensis Roques And Sun

Megastigmus likiangensis Roques and Sun belongs to Megastigmus Dalman, Megastigminae,Torymidae,Hymenoptera. It is a main pest which larvae damage endosperm in seeds of spruce trees and the damaged seeds cannot germinating. Larval and pupal development occurs entirely within a single seed, with a winter diapause that may extend to several additional years. Therefore, the development of seed trading carries the risk of introduction of this seed chalcids with seed lots. In order to provide a theory foundation for preventing against the the seed chalcid, systematical research has been carried out for the first time on the geographical distribution, damage percent, biological characteristics, the relationship between the damage and the entironment, spatial distribution of the larva of M. likiangensis in this paper. Whats more, the volatile materials from conifers cones were analyze and determine.The investigation from 2004 to 2007 indicate that M. likiangensis only damage seeds of Picea likiangensis (Franch.) Pritz.. It mostly distributes Lijiang and Diqing, Yunnan province. 5.2~22.0 percent of the spruce seeds and 41.4~81.3 percent of the spruce cones were damaged by M. likiangensis.The life history and biological characteristics of every stage of M. likiangensis are studied based on the observation in the field and observation to captive pests bred in the lab. M. likiangensis has one generation each year in Lijiang, Yunnan province. It overwinters in the seeds with larva. The adult begins to emerge in the middle ten days of June and the flourishing period appears from the late June to the early July. The amount of adult emergence is affected by air temperature and rainfall. The adult selects the oviposition site and lays eggs mainly in the basilar seeds of spruce cones. The eggs begin to hatch in the last ten days of June and pupa begin to emerge in the middle ten days of May of the followed year, the flourishing period appears from the last ten days of May to the first ten days of June. The period of larva is 10.5 month and the period of pupa is 1 month.A study was conducted on the relationships between the total number of seeds in cones of Picea likiangensis (Franch.) Pritz. and the number of seeds that were viable, infertile, infested with the larvae of M. likiangensis. Moreover, the relationship between the length of cones and its infestation with M. likiangensis was studied. Distribution percents of length of Picea likiangensis cones are consistent with the length of damaged cones by this pest. It can be supposed that cones size does not affect its infestation with M. likiangensis. The Spearman rank correlation coefficient indicated that there was a significant correlation between the total number of seeds in Picea likiangensis (Franch.) Pritz. cones and the number of viable seeds and the number of seeds infested with M. likiangensis. No correlation was found between the total numbers of seeds in cones and the number of infertile seeds.The investigation of the cone and seed in different growth periods matching with the survey of damage of M. likiangensis at the same time indicated that the damage of M. likiangensis is synchro with the growth of the cone and seed. The spruce trees in the mature stands and in the open woodland and the edge of stand were damaged more several than that in the middle-aged stands and pure stands by M. likiangensis. The damage percent of M. likiangensis to the spruce trees in different side of the hill are similar. The spruce trees at low altitude stands were damaged more several than that at high altitude stands.By investigating 5 sampling plots in the spruce forest in Lijiang, the spatial distribution patterns of larvae are determined, and the equations of optimal sampling are set up based on the regression models. Aggregated indices and regression analyses of Taylor,s Iwao,s and LAN Xingping,s methods show that the spatial distribution patterns of larvae of M. likiangensis is aggregated distribution. Among the 4 regression models, the La-m model is the best one. The aggregate result results from the environment. The equations of optimal sampling is d(n)= 2n±24.797 n .XAD2 adsorption and GC/MS were used to analyze and determine the volatile materials from the cones and bast of Picea likiangensis (Franch.) Pritz. and the cones of its sympatries, Abies georgei var.smithii and Pinus armandii. By comparing with the volatile constituent and content of Picea likiangensis, Abies georgei var.smithii and Pinus armandii cone and the bast of Picea likiangensis, found that the volatile compounds is similar but the relative content is evident difference between the cone and bast of Picea likiangensis. The volatile compounds and the relative content are evident difference among cones of Picea likiangensis, Abies georgei var.smithii and Pinus armandii. The volatile compounds and the relative content of spruce cone is correlative with the damage of the seed chalcid. This pest search hosts by distinguish- ing the difference of volatile compounds of plants. When it arrive to hosts, this pest can find ovipositing site accurately by distinguishing the difference of volatile relative content of hosts.