Studies On The Population Dynamics Of Aphis Glycines (Homoptera: Aphididae) And Its Natural Enemies Control

Through studying on the population dynamics of the soybean aphid and function of natural enemies controlling soybean aphid, certain scientific basis for the prediction of soybean aphid occurring and the theoretical foundation for utilizing natural enemies rationally to manage the soybean aphid could be offered. The dominant species of natural enemies were also confirmed. It has an important guided significance for us to artificially breed some kinds of natural enemies to control soybean aphid, and it offers the theoretical foundation for its use too. At the same time, it has important actual meanings to the integrated management of the soybean aphid.In the experiment used the method of fixed spot to systematically, the soybean aphid and the natural enemy' population dynamics in the field and combined with method of directly observation to identify the natural enemies of soybean aphid were surveyed. At the same time, population dynamics of soybean aphid and its natural enemies on the uncaged plants and caged plants in the field were also surveyed. Natural enemies were excluded by insecticide on caged experiment and analyzed changes of soybean aphid population dynamics in the condition with and without natural enemies.The main results of study as follows:1 Population dynamics of the soybean aphidThrough field survey in 2003 ~ 2004, the soybean aphid colonized the soybean field in the mid-June in Heilongjiang Province were found; and it began to disappear in the first ten days of September. There were three peaks of soybean aphid occurring in Heilongjiang Province, the first peak appeared in the middle ten days to the last ten days of June; the second peak appeared in the mid-July; the third peak appeared in the first ten days of August.Alate aphids occurred on a small quantity in mid-June in Heilongjiang Province and began to disappear in the last ten days of August. There were three big moving peaks of the aphids during the whole growth season of the soybean. One occurred in the end of June, one occurred in the first ten days August, the other occurred in the middle ten days to the last ten days August.2 Population dynamics and species of the natural enemiesSurveys in the field in 2003~2004 indicated that there were a large number of natural enemies of soybean aphid .It consisted of 5 orders, 12 families and 21 species. There were a large number of predatory spiders in addition in the field in Heilongjiang Province.The dominant species of soybean aphid natural enemies in the soybean field of Heilongjiang Province were mainly as follows: Propylaea japonica (Thunberg), Leis axyridis (Pallas), Chrysopa sinica (Tjeder), Chrysopa phyllochroma (Wesmael), Orius minutus (Linnaeus), Deraeocoris punctulatus (Fall), Epistrophe balteata (De Geer), Aphidencertus sp...3 Function of natural enemies controlling soybean aphidNatural enemies had a very good control function on the soybean aphid, and had certain actual using value in managing soybean aphid too.Hemiptera natural enemies appeared relatively early in the field, and they were one of the main controlling factors at the beginning of the soybean aphid occurring. There was an obvious following phenomenon between Hemiptera natural enemies and soybean aphid; in the later stage of soybean aphid occurring, and bacame the main factor of controlling the soybean aphid in the later stage.There were a lot of Goleoptera natural enemies in the middle period and later stage of soybean aphid occurring, and they were main controlling strength of soybean aphid in this period. But itsdominant species--Propylaea japonica (Thunberg) adult appeared relatively early in the field,and it was one of the main controlling factors of the soybean aphid at the beginning of soybean aphid occurring and reduced initial number of soybean aphids.The number of Hymenoptera and Diptera natural enemy were great in the middle period of soybean aphid occurring; the period of their peaks appeared earlier than that of soybean aphid peak, and it had an important controlling function on soybean aphid.With increasing number of soybean aphids, offered a large number of hosts for Hymeno -ptera natural enemy, the natural enemies increased sharply after soybean aphid heavy occurring, and became one of the main control factors in the later stage of soybean aphid occurring.As can be seen from the population dynamics of soybean aphid and natural enemies with appearing of soybean aphid peaks, natural enemies of each order appeared a peak immediately too, and there was a relatively obvious following phenomenon, which means that natural enemies had a better control function on the soybean aphid.4 Exclosure ExperimentThe population dynamics of soybean aphid and its natural enemies in different mesh-cages were analyzed, and the results indicated that the number of natural enemies on uncaged plants was more than that in cages, and the number of natural enemies in large-mesh cages was more than that in small-mesh cages. It correlated to the number of soybean aphid. The number of soybean aphid was the greatest in small-mesh cage, and followings were the number of soybean aphid in large-mesh cages and on uncaged plants when plants were infected artificially with soybean aphids.Each treatment was similar at the number of aphid, growing state and age of soybean. It indicated that natural enemies had an obvious control on the soybean aphid.