Octopamine Mediate Lavae Density-dependent Diseases Resistance In Mythimna Separate

Immune system plays an important role in the insect prophylaxis to pathogens.However,the regulatory mechanism of immune response underlying high-density prophylaxis is not very clear.Prelimitary results showed that a density-dependent prophelaxis was existed in the larvae M.sepatrata.In this paper,the mechanism of density-dependent prophylaxis in the lavae M.separate we investigated from the perspective of neurohormone in order to provide theoretical basis for density-dependent prophylaxis in insect.The main results are as follows:The variation of phenoloxidase(PO),the number of total hemocyte and antibacterial activity of haemolymph and resistance to Bacillus thuringiensis(Bt)and Beauveria bassiana(Bb)were investigated in the larvae M.separate reared at different larval density(1?2?5?10?30 larvae/jar)under labratory conditions(23± 1?,RH 70%±5%,photoperiod 16L:8D).The results showed the larval resistance to Bt and Bb were significantly different among five larval density treatment.The survival of larvae infected by Bt was the highest at the density of 10 larvae per jar,which was significantly higher than that of 1,2,and 5 larvae per jar.The survival of larvae infected by Bb was the highest at the density of 30 larvae per jar,and significantly higher than that of 1 and 2 larvae per jar.The variation of the number of total hemocyte and PO activity were consistent with the resistance to disease of larvae among five larval density treatment.PO activity of larvae from the 10 larvae per jar was highest,which was significantly higher than that of larvae from 1 and 2 larvae per jar.The total haemocyte count of larvae from 5,10 and 30 larvae/jar was significantly higher than of larvae from 1 and 2 larvae per jar.These results suggested that,the larval PO activitiy and total hemocyte counts of larval haemolymph were the major cause of the variation of larval resistance to disease.The levels of octopamine,5-hydroxytryptamine and dopamine of hemolymph were tested in the lavae M.Separata reared at different larval density(1?2?5?10?30 larvae per jar)by Insect Biogenic Amine ELISA Kit.The results showed larval density significantly affected octopamine and dopamine levels in the hemolymph.Octopamine level of larvae at the density of 5,10,30 larvae per jar was significantly higher than that of 1 and 2 larvae per jar.Dopamine level of larvae at the density of 1 and 2 larvae per jar was significantly higher than that of 5,10,30 larvae per jar.PO activity and the number of total hemocyte were investigated in the lavae M.separate injected with different concentrations of exogenous octopamine,dopamine and octopamine receptors antagonist/epinastine solutions.The results showed PO activity and total haemocyte count were significantly enhanced and reduced by octopamine and epinastine,respectively.And which was not significantly influenced by dopamine,.The survival rate of lavae M.separate infected by Bb and injected with octopamine was significantly higher than that of infected by Bb and injected with saline solution.Therefore,the octopamine level was the major cause of the variation of the immune and disease resistance in the larvae M.separate.The activities of tyrosine decarboxylase(Tdc)and tyramine-? hydroxylase(Tph)of head and abdomen were tested in the lavae M.Separata reared at different larval density(1?2?5?10?30 larvae per jar)using Insect Tdc and T?h ELISA Kit.The results showed larval density had a significant effect on the Tph activity,but Tdc activity was not significantly affected.T?h activity in the head and abdomen of lavae reared at the density of 10 and 30 larval per jar was significantly higher than that of at the density of 1,2 and 5 larval per jar.However,there was no significant difference on Tdc activity in head and abdomen of larvae reared among different densities.The T?h gene segment of M.Separata was obtained and its size was 811bp.The qRT-PCR results showed that the expression level of Tph gene was highest at the density of 10 larval per jar.The expression level of T?h gene of larvae reard at 10 and 30 larval per jar larvae was significantly higher than that of larvae reared at the density of 1,2 and 5 larvae per jar.Therefore,we assumed the T?h activity and its gene transcriptional level was the major cause of the variation of octopamine level in the larvae M.separate.