Study On Adaptability Of Spodoptera Frugiperda On Different Host Plants

Spodoptera frugiperda is a migratory pest in the world,since the invasion of China in early 2019,it has been successfully colonized in many areas,bring great hazard to many different crops.Host selection of S.frugiperda plays an important role in the number of population,occurrence dynamics and damage status.Relevant studies suggest that prior experience of insects results in innate preference for specific plants,which can accelerate its adaptability to experienced plant.In our study,we study biological characteristics,larvae and adults of S.frugiperda in feeding and oviposition behavior selection,the activity of protective enzymes changes and the gut microbiota species,abundance and dominance by using four plants,maize Zea mays,wheat Triticum aestivum,rice Oryza sativa and Setaira viridis to feed S.frugiperda four generations.Adaptability of S.frugiperda was made clear,The result provides a certain theoretical basis for the host range and prediction of S.frugiperda,and provide references for the prevention of S.frugiperda.The main results were as follows:1.Multi-generation feeding experience of S.frugiperda on the same host plant can shorten the developmental period significantly.The result shows that S.frugiperda feeding wheat continuously to the 4th generation,it takes only 23 d for the larvae to develop into adults,which was 5.47 d shorter than feeding wheat of the 1st generation and 1.08 d shorter than feeding corn.The developmental period of larvae fed on rice and S.viridis to the 4th generation was about 2d shorter than that of the 1st generation.The pupae weight,survival rates and number of S.frugiperda eggs increase along with the feeding generation increases.The pupae weight of the 4th generation of S.frugiperda feeding on wheat was163.13 mg,which was significantly higher than that of feeding corn(132.65mg).The survival rates(88.67%)and eggs(916.60)of S.frugiperda feeding on wheat were similar to those feeding on corn.The pupae weight,survival rate and eggs of S.frugiperda fed on rice and S.viridis showed an uptrend with the feeding generations increases,but were lower than those fed on corn.The hatching rate of S.frugiperda reared on different host plans remained high level,up to 90%.There was no significant difference in sex ratio on different host plans,which was close to 1:1.2.There is learning behavior in S.frugiperda,which is induciton of preference,in other words,the feeding and oviposition behaviors of S.frugiperda has prior host experience prefer to the previously experienced host plants,and the degree of preference was related to the time of experience and the species of host plants.After experiencing wheat,they showed a strong preference for wheat from the 1st generation.The innate feeding preference didn’t change until the 3rd generation of S.frugiperda feeding on rice.Larvae continuously fed on S.viridis to the 4th generation still prefer maize plants.In addition,it was found that the young larvae showed stronger host specificity than old larvae,the number of 2nd and 3rd instar larvae selecting preferred host up to 16,which is2-3 times that of the control plants;the preference of old larvae for the host was weakened,and the feeding options of the 4th and 5th instar larvae for different hosts were close to 1:1,there was no significant difference..The oviposition selection of adults fed on multiple generations for the same host is similar with the feeding preference of larvae,suggest that feeding experience of larvae could affect the host selection of adults.3.Feeding on different host plants had significant effects on the activities of protective enzymes.The activities of catalase(CAT),peroxidase(POD)and superoxide dismutase(SOD)in the 1st–3rd generations of S.frugiperda fed on wheat,rice and S.viridis respectively were higher than those fed on corn.The results show that feeding on unsuitable host plants could induce the activity of protective enzymes.The activity changes of three protective enzymes of S.frugiperda fed on wheat,rice and setaria were not consistent.CAT,POD and SOD activities of S.frugiperda larvae fed wheat decreased from the 2nd generation.The activities of CAT and POD of S.frugiperda larvae fed rice continued to rise in the 2nd generation,and decreased until the 3rd generation;SOD activity decreased along with the feeding generation increases.The activities of CAT,POD and SOD of the 1st to the 3rd generation of S.frugiperda larvae fed on S.viridis remained high.It is concluded that feeding on wheat was more beneficial to the development of S.frugiperda,the protective enzyme system in S.frugiperda fed wheat could be adjusted to the normal level quickly.S.viridis is the least suitable for S.frugiperda,maintaining high protective enzyme activity for multiple generations requires a large amount of energy consumption of larvae,which is not conducive to population growth.4.The gut microbiota of the 5th instar larvae of S.frugiperda feeding on artificial diet,corn,wheat and S.viridis was analyzed.The results showed that gut microbiota belonged to 28 phylums,6 classes,159 orders,284 families,595 genera and 660 species.The species of gut microbiota of S.frugiperda feeding different hosts almost the same,but dominant phylum and microbial abundance was different.The dominant phylum of S.frugiperda larvae feeding artificial diet was Proteobacteria(40.97%),and the major phylum of the 1st generation of S.frugiperda larvae transferred to corn,rice and wheat was Firmicutes,relative abundance is 35.98%,32.92% and 36.43%,respectively.Compared with the 1st generation,there was not significantly different change in the gut microbial diversity of S.frugiperda larvae fed the same plant until the 3rd generation,but only the relative abundance of microbia changed,at the genus level,compared with the 1st generation,the Enterococcus genus of the 3rd generation larvae feeding wheat and rice decreased by 9.22% and 5.34%,respectively,and the Enterococcus genus of the 3rd generation larvae that feeding S.viridis increased by 18% compared with the 1st generation,becoming the predominant bacterial genus of the 3rd generation.These results indicated that S.frugiperda adapted to food changes as soon as possible through adjusting the relative abundance of different microbial communities,and the mechanism of this effect needs further study.