Study On The Fitness Of Aphids On Mythimna Separata-infested Bt And Non-Bt Corn Plants

In the natural ecosystem,there are close interspecific relationships among plant-mediated herbivores,such as competiton,mutualism and altruism.In this way,when the population of a herbivore changes,it will inevitably affect the population dynamics of other related insects.Because insect-resistant genetically engineering plants that express insecticidal Cry proteins derived from Bacillus thuringiensis(Bt)have better control effects on target pests,the cultivation of Bt crops will significantly reduce the population of target pests,which will affect the population dynamics of non-target insects that are closely related to target pests.For example,previous studies have shown that the reduction of target pest pests on Bt cotton resulted in a higher density of non-target pest cotton aphid.Similarly,the study also found that the long-term cultivation of Bt corn could also lead to an increase in the population of non-target pests such as aphids.But whether this is related to the reduction of target pest damage on Bt corn has not been reported.So,we chose Bt corn and non-Bt cron,the target insect Mythimna separata and the non-target insect aphid Rhopalosiphum maidis,carried out laboratory biometric test,greenhouse experiment and field experiment,and explored the fitness and the population dynamics of aphids on M.separata-infested or uninfested corn,to analyze the impact of large-scale long-term planting of Bt corn on the population dynamics of aphids.The mianly results were following:1)The life history and population dynamics of R.maidis on M.separata-infested and uninfested corn in the laboratory experiments research showed that: compared with the healthy maize plants,for the aphids feeding on M.separata-infested corn,the nymph development period is extended,the adult development period is shortened,the total development period is longer,the survival rate is reduced and the number of offspring is reduced.The diffierences are significantly.We also analyzed the population parameters of corn aphid and found that instrinsic rate of increase,net reproductive rate,and finite rate of increase of aphids population by fed on M.separata-infested corn were also significantly lower than fed on the healthy corn,while the mean generation time was significantly longer too.2)The population dynamics of R.maidis on Bt and non-Bt corn under the condition of the presence or absence of M.separata were studied by greenhouse experiment.The results showed that there was no difference in the growth,development and fecundity of aphids on uninfested Bt and non-Bt corn.However,in the presence of armyworm,compared with non-Bt corn,M.separata caused very little harm to Bt corn,so the population growth rate of aphid on Bt corn was significantly higher than that on non-Bt corn.3)The population of aphids on Bt and non-Bt corn was investigated by field experiment.The results showed that under natural conditions,although lepidoptera insects were found to be harmful on non-Bt corn,but the degree of harm was low.As a result,the population density of aphids on Bt corn was significantly higher than that on non-Bt corn,but the difference was not significant.However,when we put the M.separate on the Bt and non-Bt corn,the damage caused by M.separate to Bt corn was significantly lower than that to non-Bt corn,so the number of aphids population on Bt corn was significantly higher than that on non-Bt corn.This study showed that Bt corn had no negative effect on aphid development and population growth.However,whether Bt corn or non-Bt corn,M.separata infestation could induce corn defense response and improve corn resistance to aphid.Due to the resistance Bt corn to M.separata,the damage degree of Bt corn is significantly reduced.Compared with non-Bt corn,which is seriously damaged by M.separata,Bt corn is more conducive to aphid development and population growth.This study showed that the reduction of target pest infestation on Bt corn may lead to the growth of non-target pest populations,and elucidated the potential ecological mechanisms underlying the effect of Bt crops on non-target herbivore species,which provides a scientific basis for the comprehensive prevention and control of field pests in the future after commercial planting of Bt corn in China.