The Control Of Aphidius Gifuensis Ashmead To Myzus Persicae(Sulzer) In The Tobacco Fields

Myzus persicae(Sulzer)is a world pest and one of the major pests on tobacco leaves.The tobacco leaves are seriously endangered and occur throughout the growth period of the tobacco.The pricked smoking tobacco juice leads to the reduction of the quality of the tobacco leaves,and the secreted honeydew can induce the coal loss resulting in the production of tobacco leaves.M.persicae have occurred in all tobacco-planting areas in China,occurring in more than 20 generations in Jiangxi Province.Aphidius gifuensis Ashmead,a dominant parasitoid of M.persicae,has a parasitism of 20%?60%and a maximum of 90%in the field,which is significant in the biological control of persicae significant effect.Although has achieved remarkable results in Yunnan and other places,it still has some limitations in its production,which are mainly manifested in its slow control effection,instability of control effection,climate and regional ecological environment However,it is still impossible to fully,timely and effectively meet the current needs of pest control in tobacco intensive production in various regions.This paper explored the population dynamics of M.persicae and its major natural enemies in main planting areas of Jiangxi Province,the plant-mediated support system of natural enemies,diapause rate under different temperature and light conditions,toxicity and field control of insecticides commonly used in fields to M.persicae.2015-2017 field survey results showed that the population dynamics of M.persicae in the field showing a clear bimodal curve.The first peak of M.persicae occurred in late April and early May,with an average of about 1000 aphids per 100 plants.The second peak occurred in late May.There was a clear follow-up relationship between M.persicae and A.gifuensis with two peak periods,which were basically consistent with the peak period of M.persicae in the field.There was only one peak period for the natural enemies of spider mites,including the grasshopper,the ladybug,the hoverfly.The number of other natural enemies is not obvious.After releasing A.gifuensis in the field,the parasitism rate reached the highest after 15 days,the average parasitism rate was above 50%,and the parasitism rate decreased after 21 days.The number of M.persicae decreased,and the rate of decline in the population of insects increased 21 d after putting the A.gifuensis in the field was between 74%?90%.In this study,the population dynamics of M.persicae and A.gifuensis and the parasitic rate in tobacco field and other crops were studied.The results showed that the number of aphids in rapeseed was the most,while the number of aphids in pepper and cabbage was relatively less.It is obvious bimodal.The number of natural enemies in rapeseed was the highest,the highest number of A.gifuensis was 62 per 100.The highest number of other natural enemies such as hoverflies,weeds and spiders was 70/100.Enemies on the pepper,cabbage around the tobacco fields are relatively small.The number of parasitoids and other natural enemies and the parasitism rate of M.persicae in the tobacco fields near rapeseed field were higher than those in the common tobacco fields.Therefore,the rape can be used as the banker plant of the natural enemies,while the pepper,cabbage can be used as the habitat plant.Diapause changes of A.gifuensis were examined under variable temperatures,photoperiods and their combinations.The results show that at the temperature was 0?,5?,10? under the short day length(L:D = 8:16),the diapause rate of the wasps was 71.12%,55.50%and 45.71%,respectively,while the rate decreased to 44.53%?24.18%and 0 at the same temperature under the long day length(L:D=14:10).However,the parasitoid wasp was not induced into diapause when they stored at 25 ? and 30? under either long day length or short day length.The present study indicates that the interaction of low temperatures and short day length could induce more individuals A.gifuensis into diapause,while long day length and high temperatures inhibit the wasps' diapause occurring.The days of cold storage were 5d,10d,20d,25d,30d,40d,50d and 60d respectively.The results showed that with the prolongation of the cold storage time,the emergence rate,longevity and parasitism rate of the A.gifuensis were gradually decreased and the diapause rate increased gradually.When the cold storage time reached 60 days,the emergence rate was only 30.21 d;the average life span was 2.97 d;the parasitic rate decreased to 39.46%;the diapause rate was 39.85%.Therefore,the experimental results showed that the best frigeration preservation time of the A.gifuensis which development for three days should be within 30d.Long-term use of chemical insecticides not only increases the resistance of aphids,but also can damage the M.persicae.In order to choose the best insecticide to control the M.persicae,but less toxic to the A.gifuensis,we studied the effects of 6 insecticides commonly used in the field on the insecticides M.persicae and A.gifuensis.The virulence of braconidae was measured and its control efficacy against M.persicae was determined.The results showed that the insecticides were toxic to M.persicae in the following order:dinotefuran>acetamiprid>pymetrozine>nitenpyram>imidacloprid>avermectin;The insecticides were toxic to A.gifuensis in the following order:acetamiprid>nitenpyram>dinotefuran>avermectin>pymetrozine>imidacloprid.Seven days after spraying,the antifungal efficacy of all the pesticides was above 90%,of which 25%pymetrozine water dispersible granules had the highest efficacy(98.40%)against M.persicae.Based on the above indoor and outdoor test results,pymetrozine can be used as a selective insecticide in the chemical control of aphids,while insecticides such as nitenpyram and dinotefuran can be avoided as far as possible.Effective control of aphids can protect A.gifuensis such as the role of callus.