Immune Response Induced By Beauveria Bassiana And Its Interaction With Flight Of The Oriental Armyworm,Mythimna Separata (Lepioptera: Noctuidae)

Migration and immunity are the behavioral and physiological countermeasures against different selective pressures or invasion of foreign substances formed in the process of insect long-term adaptation to environmental changes.It is of great theoretical and practical significance to study the interaction between migration and immunity,to elucidate the interaction between the two,to understand the adaptive significance of migratory flight in insect evolution,and to analyze the disaster mechanism of migration.This experiment by Mythimna separata this major agricultural pests as the object,Beauveria bassiana infection in injection and set different concentration as a means of processing,research on the growth and development,reproductive ability,the ability to fly,and the effects of parental flight treatment on the development and immune ability of the offspring,systematically to study the interaction relationship between immunity and migration.1.The effects of Beauveria bassiana infection on the growth,development and immune responses of migratory and resident M.separata and their differences were studied.The migratory M.separata larvae under high density had stronger immune reaction than the resident larvae,which led to their resistance to Beauveria bassiana infection was significantly higher than that of the resident larvae.The results showed that the corrected mortality of migratory（10 heads/bottle）and resident（1 head/bottle）larvae in different densities increased with the increase of concentration after injected with different concentrations of Beauveria bassiana.Among them,the adjusted mortality of resident M.separata increased significantly with the concentration of 5×10⁵spores/ml,while that of migratory M.separata larvae increased significantly with the concentration of 5×10⁶spores/ml.Moreover,migratory M.separata larvae were more resistant to Beauveria bassiana infection than the resident type.The corrected mortality of migratory larvae at high concentrations（10⁶,5×10⁶and 10⁷spores/ml）was significantly lower than that of resident larvae.LC₅₀（8.03×10⁶spores/ml）of migratory M.separata was 3 times higher than that of resident M.separata.In addition,Beauveria bassiana injection had a significant effect on pupa weight,emergency rate and developmental period of migratory and resident M.separata.The pupa weight of resident M.separata decreased significantly at 5×10⁵,10⁶and 5×10⁶spores/ml,while the pupa weight of migratory type decreased significantly at 10⁶,5×10⁶spores/ml.Meanwhile,the emergency rate of migratory and resident adults decreased significantly with the increase of treatment concentration,and the influence of concentration on the emergency rate of resident adults was more significant.The emergency rate of resident adult significantly decreased from 10⁵spores/ml,while that of migratory adult significantly decreased when treated with a higher concentration（5×10⁵spores/ml）.The developmental duration from the 6th instar larva to adult emergency rate of resident M.separata was significantly longer than the control group from 4×10⁵spores/ml and migratory M.separata’s from 10⁵spores/ml.In addition,the infection of Beauveria bassiana can induce the immune nodule of M.separata,and the migratory M.separata larvae have stronger immunity against Beauveria bassiana infection than the resident type.Within 84h of injection,the number of nodule increased with time,but did not increase significantly thereafter.In addition,the number of nodule of migratory and resident M.separata larvae increased significantly with the increase of concentration.In addition,at high concentrations（10⁶,5×10⁶spores/ml）,migratory M.separata had a strong nodule reaction,and the number of nodule was significantly higher than that of the resident type.2.The study clarified the influence of Beauveria bassiana infection on the reproduction and flight of M.separata:the reproductive cost of the migratory type with high concentration of Beauveria bassiana infection was lower than that of the resident type;However,the low concentration of Beauveria bassiana infection does not sacrifice the flying ability of M.separata,and the enhancement of the flying ability of resident type is greater than that of migratory type.It was found that the high concentration of Beauveria bassiana infection had a negative effect on the reproduction of migratory species and resident species,but the negative effect on resident species was stronger.The total spawning capacity of the migratory type was significantly lower than that of the control type under 5×10⁵and 10⁶spore/ml treatment,while that of the resident type was significantly lower under 10⁵/ml,5×10⁵and 10⁶spore/ml treatment.At the same time,Beauveria bassiana infection had no significant effect on the preoviposition of migratory type,but the preoviposition of resident type treated with 5×10⁵and 10⁶spores/ml was significantly prolonged.In addition,the5×10⁵spore/ml treatment significantly shortened the oviposition period of the migratory type,while the resident type significantly shortened the oviposition period of the 5×10⁵and10⁶spore/ml treatment.However,the influence of high concentration of Beauveria bassiana infection on the life span,mating frequency and mating rate of migratory and resident males was the same,which led to the significant shortening of both species.The low concentration of Beauveria bassiana infection in the larval stage had a significant effect on the flight ability of both migratory and resident M.separata adults,but the effect was higher in the resident than in the migratory type.Among them,although the flight ability of adult migratory M.separata increased to a certain extent after the infection of Beauveria bassiana at low concentration in the larval stage,the flight time of female only increased significantly under the treatment of 5×10⁴spores/ml.The flying distance of the resident female was significantly increased under the concentrations of 10⁴and 5×10⁴spores/ml and the flying distance was significantly increased under the concentrations of 10⁴,5×10⁴and 10⁵spores/ml.In addition,the flight time and distance of resident males were significantly increased under treatment of 10⁴and 5×10⁴spores/ml.Moreover,although the flying ability of the uninfected resident M.separata was significantly lower than that of the migratory type,there was no significant difference between the flying ability of the resident adults infected with medium and low concentrations of Beauveria bassiana in the larval stage and that of the migratory type treated with the same concentration.The results showed that the low concentration of Beauveria bassiana infection significantly enhanced the flight ability of migratory and resident M.separata,and enhanced their tendency of escaping from the bad environment.3.The effects of Beauveria bassiana infection and flight stimulation on the its reproduction,development and immune defense ability of the offspring of adults were determined.The 2-nights flight did not sacrifice the reproductive ability of parents and the immune defense ability of progeny.On a 5-nights flight,the opposite is true.The infection of Beauveria bassiana at larval stage had no significant effect on reproduction and development and survival of progeny,and did not change the effect of flight on reproduction and immune ability of progeny.It was found that the effects of different flight treatments on the reproduction of parents and the development of offspring larvae were also significantly different:After two consecutive nights of flight stimulation,the fecundity increased,the preoviposition shortened,and the oviposition synchronicity increased.Compared with the control group,the hatching rate,mortality rate and emergency rate of the offspring larvae of the migratory parental adults had no significant changes.However,after 5-nights of sling treatment,the fecundity decreased and the preoviposition prolonged,which had a significant negative effect on the development of offspring.For resident parents,flight stimulation for 2 nights did not promote reproduction and had no significant effect on the growth and development of offspring,while flight stimulation for 5 nights inhibited reproduction and development of offspring in the same way as migratory parents.However,the low concentration of5×10⁴spores/ml at the sixth instar larval stage did not significantly affect the reproduction of the adults and progeny growth,nor did it change the effect of flight on the reproduction and progeny growth.In addition,the effects of different flight treatments on the immune resistance of offspring larvae to Beauveria bassiana infection were also significantly different.When parental adults were exposed to flight stimulation that promoted or did not affect their reproduction（corresponding to migratory type and residence type）,flight had no negative effect on their immune defense ability.The number of nodules and PO content of offspring larvae infected with 5×10⁶spores/ml Beauveria bassiana had no significant change compared with the control.The corrected mortality of its offspring larvae was not significantly different from that of the control.However,when the parents were subjected to flight treatment to inhibit reproduction,flight significantly reduced the immune defense ability of their offspring,which showed that the adjusted mortality rate of Beauveria bassiana larvae was significantly increased,and the number of nodules and the content of PO were significantly decreased.However,expect the low concentration of 5×10⁴spores/ml of Beauveria bassiana at the 6^thinstar larval stage increased the PO content compared with that of the non-flying resident parents,and the parental larval stage immune stimulation did not reduce or enhance the immune cost of the offspring caused by flight.