Study On The Effect Of Different Field Treatments On The Population Dynamics Of The Hippodamia Variegata(Goeze) And The Control Of Aphis Gossypii

Aphis gossypii is the main injurious insect to the Xinjiang Cotton and Hippodamia variegate is the natural enemy of A.gossypii.In order to study the control effects of H.variegate on cotton aphid,the paper explored the dynamics of H variegate and suppression on A.gossypii under various field management measures.The main achievements are as follows:1.H.variegate and their population structure under artificial migration were studied for the control effects on A.gossypii.Results show that: in the boll period of the cotton,the amount of A.gossypii was significantly reduced compared with CK when a ratio of H variegate vs A.gossypii is 1:1000.15 d after artificial migration,the amount of A.gossypii got close to that of the chemical prevention field(TCPF).The control efficiency of TCPF and biological prevention field(TBPF)were 82.22% and 83.81%,respectively.The amount of H variegate in each worm form reached the maximum in the peak period.Changes of the amount of larva and imago of H variegate in TBPF were proportional to the control efficiency,and the amount of pupa was in inverse proportion to the control efficiency.In TCPF,changes of the amount of pupa and larva were proportional to the control efficiency,but their quantity was significantly lower than that in TBPF.Results show that H variegate under artificial migration with a H variegate/A.gossypii ratio of1:1000 can well control the A.gossypii,and the control effects were stable and durable.2.Difference of the occurrence quantity of the injurious insect and their natural enemy in four cotton fields were measured.Results show that the amount of A.gossypii and ant in the fields from high to low were: natural cotton field(NCF)>cotton field with unilateral chemical prevention(CFWUCP)>cotton field with bilateral chemical prevention(CFWBCP)>cotton field chemical prevention(CFCP)..The amount of metabolous insects including H variegate from high to low were: CFWBCP>NCF>CFWUCP>CFCP.Various metabolous insects all have migration to some degree.Therefore,CFWBCP is recommended to prevent A.gossypii.3.Difference of the quantity changes of A.gossypii and H variegate from the artificial topping field(TATF)and the chemical topping field(TCTF)was measured.Results show that in the same period the amount of A.gossypii was the largest in the field without topping(TFWT),and the reduction ratio of A.gossypii was slow relative to the topping field.7 days after chemical topping,the proliferation ratio of natural enemy was significantly higher than that of TATF,indicating a potential of biological prevention.In the early stage of topping,TCTF showed the lower prevention efficiency than TATF,but the inflexion of increasing of TCTF was 3 days earlier than that of TATF.Therefore,putting H variegate in TCTF is recommended for a higher prevention efficiency.