| Serangium japonicum is an important predator of Bemisia tabaci in China and has great potential to be developed as a biocontrol agent.The search for suitable alternative prey will promote the mass rearing of this predator.However,there are few relevant studies.In the present study,we examined the development and reproduction of S.japonicum,and evaluated the ovarian phenotype and analyzed transcriptome sequencing data between S.japonicum feeding on Bemisia tabaci eggs and nymphs and feeding on Ephestia kuehniella eggs.The main findings are as follows:（1）Serangium japonicum feeding on E.kuehniella eggs grow well but lay very few eggs.Comparing with S.japonicum feeding on B.tabaci eggs and nymphs,S.japonicum feeding on E.kuehniella eggs significantly prolonged the development duration from 1st instar larvae to adult emergence for about 1 d,sharply decreased the weight of 4th instar larvae（24 h old）,and increased the weight of adult males（24 h old）,but did not significantly change the survival rate from 1st instar larvae to adult emergence,sex ratio,and the weight of adult females（24 h old）.Comparing with S.japonicum feeding on B.tabaci eggs and nymphs,S.japonicum feeding on E.kuehniella eggs during the adult stage significantly increased the longevity of both adult males and females,but greatly reduced the oviposition day and fecundity,and markedly decreased population parameters such as the net reproductive rate（R0）,the finite rate of increase（λ）,and the intrinsic rate of increase（r）.（2）The structure of the female inner reproductive organs is intact,but the ovarian development is obviously delayed by feeding on E.kuehniella eggs.The deposition rate of egg yolk in the ovary was much slower when feeding on E.kuehniella eggs than on B.tabaci eggs and nymphs,and the day for the appearance of egg yolk deposition and mature oocytes was significantly prolonged for about 1 d and 20 d,respectively.The number of oocytes in the ovary was reduced.The length of ovariole increased slowly as well;it was about 40%shorter when feeding on E.kuehniella eggs than feeding on B.tabaci eggs and nymphs.（3）When transferred from feeding on B.tabaci to feeding on E.kuehniella eggs during the adult stage,S.japonicum stopped laying eggs,and vice versa.Therefore,the RNA of 14 day-old adult females feeding on B.tabaci only and 14 day-old adult females feeding on B.tabaci first for seven days and then transfer to E.kuehniella eggs for another seven days were extracted and sequenced for transcriptome analysis.The results revealed that there are 1,229 differential expression genes between those two treatments,with 267 and 962 genes significantly increased and decreased in expression after feeding on E.kuehniella eggs,respectively.Five important genes that are differentially expressed in the nutrient and juvenile hormone signaling pathways,such as TOR,PI3K,S6K,ALDH,and JHAMT,were screened out.In addition,we found two largely and differentially expressed vitellogenin genes,Vg1 and Vg2.Overall,E.kuehniella eggs are beneficial to the development of S.japonicum from neolarvae to adult emergence but detrimental to reproduction because ovary development and oocyte maturation are inhibited,and the expression of important genes in nutrient and insect hormone signaling pathways is significantly reduced.Ephestia kuehniella eggs can only be used as an alternative prey for mass rearing S.japonicum larvae. |
