| The oriental armyworm Mythimna separate(Walker),a major migrant pest of grain in China,shows a typical density-dependent phase polymorphism.In recent years,the investigation of the nationwide found that the different degree of black larvae had become a typical disaster warning of the population,and the gregarious insects resistance to natural parasitism and pathogen infection is significantly increased,some biological agents also have no obvious control effect.Therefore,this experiment is based on systematically investigation of density-dependent melanization and the corresponding defense capacity in this species,and then determine the changes of hemolymph related immune indexes after exposure to the pathogen,which benefits to unveil the triple organic connections among density-dependent melanization,defense capacity and immunity.Furthermore,we discussed the effects of dopamine(DA)and 5-hydroxytryptamine(5-HT)on the defense ability and immune index in this species.Finally,survival larval feeding and emergenced adults flight and reproduction performance after infection with pathogen will be comprehensively identified.This project will illustrate density-dependent defense response mechanism and provide theoretical and experimental support for disclosing the gregarious form disaster cause and guilding field biological control in Mythimna separate.The results were summarized as follows:Difference of immunity response between gregarious and solitary phases of the oriental armyworm,Mythimna separate(Walker).The results showed that the hemolymph protein content of gregarious larval is significantly higher than the control after 6h infected by Metarrhizium anisopliae,while the solitary larval is significantly reduced;and the PO activity of gregarious larval is significantly enhanced than solitary larval.Meanwhile,gregarious larval immune response is rapid and sustained.The lysozyme activity of gregarious larval has significantly enhanced after 6h infection,while the solitary type increased significantly until infected 48 h.Study on antibacterial activity showed that it can induce the activity elevation in the early stage of infection and later decreased in gregarious larval;While the solitary larval has a serious of similar changes with gregarious larval in the early stage of infection,it is significantly higher at 72 h and then decline.Study on cellular immunity showed that the total number of blood cells in gregarious larval increased significantly at 6h and 24 h after infection,while the solitary larvae just significantly increased in 48 h.Futher analysis about the percentage of plasmatocyte and granulocyte found that after 6h,24 h,72h infection,the percentage of plasmatocyte increased significantly in gregarious larval;while in the solitary larval,two types of haemocytes have significantly increased only at 24 h.Therefore,we speculate that the gregarious larval may have a more active immune system,it has a greater advantage on immune activation and the maintenance of immune energy,mainly reflected in the rise of major immune index and the sustained of immune response.Difference of immune neuroregulation between gregarious and solitary phases of the oriental armyworm Mythimna separate(Walker).Study on neurotransmitter DA found that the content and changes of hemolymph DA have a obvious differences between the gregarious and solitary larval.The content of hemolymph DA in gregarious larval were higher than the control at each time after infection,while the solitary larval is only at 6h was significantly higher than the control.Study on neurotransmitter 5-HT found that the content of hemolymph 5-HT in gregarious larval were significantly increased at each time except 72 h after infection,while the solitary type only at 6h increased significantly,it is decreased at the other time.Further research effect of neurotransmitter DA and 5-HT injection on the immune system of the gregarious larvae,the results showed that the immune factors of gregarious larval have different response of two types of neurotransmitter.After injection with biological amine hydrochloride,the PO activity,antibacterial activity in the gregarious larval were significantly higher than control group,while although the protein content and lysozyme activity also increased,but compared to the control group it has no significant difference.Meanwhile,injection of biogenic amine neurotransmitter also has a significant impact on defense capability of gregarious larval.DA injection can significantly improve the gregarious larval resistance of Metarhizium anisopliae,its pupa weight also increased correspondingly.These results suggest that biogenic amines can cause the activation and release of armyworm immune system,resulting in changes of immune factor,this is a kind of immunological stress on insect,which is instead of immune response caused by pathogens invasion.Effect of larval defense response on flight and reproduction capacity of adult oriental armyworm Mythimna separate(Walker).The results of the study showed that the Metarhizium anisopliae infection have a significantly influence on flying ability,the adult flight ability were all enhanced,and the ratio of strong flight individual increased,but the adult of gregarious larval to enhance the ability of flight more obvious,the flight time and flight distance were significantly higher than control,while the reproduction and longevity of adult of solitary and gregarious larve after infection did not change significantly.These results indicate that Metarhizium anisopliae infection against flying ability had a greater effects than the reproductive ability,and flight capacity enhancement may be a kind of adaptive behavior on armyworm to avoid adverse environment.the variances of immune ability and behavior pattern between solitary and gregarious larval result in differences in behavior and development direction after infection. |
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