| Aphis gossypii and Acyrthosiphon gossypii are two coexisting aphid species on cotton,showing seasonal differences in abundance in Xinjiang,China.Acgossypii does not affect cotton with non-aggregating habit and has more competitive advantage because of occurring early consequently in the season before A.gossypii in the field.In the pest management practices,Ac.gossypii could attract and cultivate a large number of natural enemies in favour of reducing greatly the outbreak and heavily infests of cotton aphids in the later period of cotton.In recent years,there are significant changes of the new pattern of relationship between A.gossypii and Ac.gossypii,and A.gossypii damages increasingly with changing into dominant species pests in Southern Xinjiang transgenic Bt cotton-growing region.Based on the new pattern of relationship between A.gossypii and Ac.gossypii in Southern Xinjiang transgenic Bt cotton-growing region,the driving mechanism of competitive displacement between A.gossypii and Ac.gossypii were investigated in this study.It is important to study direct and indirect impact of transgenic Bt cotton on interspecific competition relations and the difference of sensitivity to pesticides of two aphids.The results of this research program are not only helpful for exploring the rules of competitive displacement reactions between secondary pests and the main pests,but also helpful for understanding the deep impact of transgenic Bt cotton on community of non-target pests.Summarizing all the results we got following conclusions:(1)The investigation of the marketing of cotton seeds showed that the proportion of transgenic Bt cotton seeds were increased in 2014-2016 in Southern Xinjiang.The proportion of transgenic Bt cotton seeds has accounted for 79.69%in 2016,which significantly higher than 2013.These results demonstrated that the growing of transgenic Bt cotton in Southern Xinjiang was expanding in these years.The field surveys in the Southern Xinjiang showed that A.gossypii was the dominant pest species in the early growth period of cotton,and the population of Ac.gossypii declined significantly.Besides,the densities of the field population of A.gossypii and Ac.gossypii showed a negative correlation.However,when pesticides were applied the population density of A.gossypii increased 19.37%,14.07%and 9.67%in transgenic Bt cotton,non-transgenic cotton and Xinluzhong 54,respectively.(2)The results of feeding selection and competing relationship between A.gossypii and Ac.gossypii showed that the selection rate,the fecundity of aphids and the interspecific competition have no significant difference between different cotton cultivars.The environmental capacity and intrinsic rate of increase(rm)of A.gossypii in three cotton cultivars were 2138 aphids/plant,2243 aphids/plant and 2310 aphids/plant,and 8.65 times,8.38 times and 8.85 times significantly higher than the highest density of Ac.gossypii.Further,we found that rm of these two species was higher when they occurred separately in cotton plant.The impacts were asymmetric between interspecific competition and intraspecific competition for Ac.Gossypii in the crowded conditions.(3)The life table parameters showed that the developmental duration and survivorship rate of Ac.Gossypii and A.gossypii were 7.42 d,8.42 d,8.22 d and 5.68 d,6.27 d,6.39 d;84.29%,81.31%,82.88%and 83.07%,80.52%82.29%on three cotton varieties(CCRI41,CCRI23,XLZ54)respectively.There were no significant differences on different cotton varieties.The developmental duration and time of double population of Ac.gossypii were greater compared to A.gossypii on different varieties,but net reproductive rate(R0)and intrinsic rate of increase(rm)were lower than A.gossypii.A.gossypii had greater potential fecundity compared to Ac.gossypii.(4)Coccinella undecimpunctata is one of the natural enemies of A.gossypii and Ac.gossypii,and the results of a/Th of 1st-4th instar larvae and adult analysis demonstrated were 1.21?53.65?71.75?148.30?143.33 to A.gossypii,and 2.08?46.83?46.07?36.59?112.01 to Ac.Gossypii respectively.C.undecimpunctata had greater control ability to A.gossypii than to Ac.gossypii.Prey selection index of C.undecimpunctata to A.gossypii was increased as the increasing of selection effect,and the adults exhibited higher selection effect than nymphs.When A.gossypii and Ac.gossypii coexist on cotton plant,C.undecimpunctata preferred to prey A.gossypii,and as the ratio of the density of A.gossypii to Ac.gossypii decreasing the control ability of C.undecimpunctata to aphids enhanced significantly.(5)The results showed that the aphid population density were 52600 aphids/100 plants and 53333 aphids/100 plants on Bt cotton varieties(CCRI41)and parent cotton varieties(CCRI23)and 30.06 times,and 23.95 times significantly higher compared with total elimination of natural enemies.The dominant natural enemies and the assemblage of other arthropod natural enemies were similarly abundant in transgenic Bt cotton and non-transgenic cotton fields,the top-down forces were equally strong in both plots.(6)The results showed that A.gossypii field populations collected from three cotton regions exhibit higher LC50 values to imidacloprid and acetamiprid than the field populations of Ac.Gossypii in Southern Xinjiang.The LC50 values of A.gossypii to imidacloprid were 22.31,20.42 and 15.53 mg/L,respectively,which were 3.1,3.0 and 2.9 times higher than the LC50 values of Ac.gossypii.Similarly,the LC50 values of A.gossypii to acetamiprid were higher than Ac.gossypii populations,which were 42.35,45.63 and 30.27 mg/L in three field populations.Besides,the results demonstrated that the average development duration,intrinsic rate of increase(rm)and population double time of F1 generation were deceased significantly in the treatments of imidacloprid and acetamiprid in comparison with control.However,the intrinsic rate of increase of F1 generation was increased following the treatment of these two pesticides in both aphid species. |
PDF Full Text Request