Larval development and voracity of Eupeodes americanus (Diptera: Syrphidae): comparison of the focal prey Aphis gossypi (Hemiptera: Aphididae) and the banker prey Rhopalosiphum padi (Hemiptera: Aphididae)

Unlike European species,the potential of Nearctic syrphids as biological control agents is still poorly studied.However,the American hoverfly,Eupeodes americanus(Wiedemann),has recently demonstrated promising traits as a biocontrol agent,notably against the foxglove aphid,Aulacorthum solani Kaltenbach,on pepper.The present study aims to extend our knowledge of the American hoverfly by evaluating its potential as a biocontrol agent in a banker plant system against the melon aphid,Aphis gossypi Glover,in a greenhouse cucumber crop.The preimaginal development and voracity of E.americanus were compared when preying upon the focal prey/pest(A.gossypi)or the banker prey(bird cherry-oat aphid,Rhopalosiphum padi L.)by daily observations of larvae from egg to adult.Preimaginal development time,survival rate,and occurrence of deformation were similar on both prey species.The weight of third instar and pupae,however,was higher for larvae that fed on the banker prey.The ad libitum voracity of the syrphid larvae was generally very high and did not significantly differ between prey species,except for the third-instar larvae which consumed more focal prey.Results suggest that a banker plant system involving the bird cherry-oat aphid may be a promising tactic for utilizing E.americanus for melon aphid biocontrol.

RpUGT344J7 is involved in the reproduction switch of Rhopalosiphum padi with holocyclic life cycle

Many aphid species exhibit both cyclical parthenogenesis(CP)and the obligate parthenogenesis(OP)life history,which are genetically determined.In CP aphid lineages,the parthenogenetic individuals can switch from asexual to sexual reproduction quickly in response to environmental factors such as changes in photoperiod and temperature.However,the OP aphid lineages do not undergo sexual reproduction under any conditions.So far,mechanisms underlying the reproduction switch in CP aphids have not been fully elucidated.Rhopalosiphum padi,a serious worldwide insect pest of wheat,has both CP and OP lineages.Uridine diphosphate-glycosyltransferases(UGTs)are enzymes that participate in the metabolic detoxification of xenobiotics.Here,we identified 43 RpUGT genes from R.padi genome and transcriptome sequences,and found that:(1)the UGT content of the CP lineage was significantly higher than that in the OP lineage at the key time points when CP lineage mainly produce virginoparae,gynoparae,and males under inducing condition,while there were no significant difference under normal conditions;(2)RpUGT344J7 gene was highly expressed during the time points when CP lineages produce gynopara and males;(3)the critical time points for CP lineages to produce virginoparaee,gynoparae,and males were affected when the CP lineages were injected with dsRpUGT344J7;(4)the knockdown of RpUGT344J7 caused a significant reduction in the total number of virginoparae,gynoparae,and males in the offspring under inducing condition.The findings contribute to our understanding of the molecular mechanisms underlying the quick shift from asexual to sexual reproduction in aphid species.

Diurnal feeding as a potential mechanism of osmoregulation in aphids

Diurnal variation in phloem sap composition has a strong infuence on aphid performance.The sugar-rich phloem sap serves as the sole diet for aphids and a suite of physiological mechanisms and behaviors allowv them to tolerate the high osmotic stress.Here,we tested the hypothesis that night-time feeding by aphids is a behavior that takes advantage of the low sugar diet in the night to compensate for osmotic stress incurred while feeding on high sugar diet during the day.Using the electrical penetration graph(EPG)technique.we examined the eiects of diurmal rhythm on feeding behaviors of bird cherry-oat aphid(Rhopalosiphurm padi L.)on wheat.A strong diurmal rhythm in aphids as indicated by the presence of a cyclical pattern of expression in a core clock gene did not impact aphid feeding and similar feeding behaviors were observed during day and night.The major difference observed between day and night feeding was that aphids spent significantly longer time in phloem salivation during the night compared to the day.In contrast,aphid hydration was reduced at the end of the day-time feeding compared to end of the night-time fepding.Gene expression analysis of R.padi osmoregulatory genes indicated that sugar break down and water transport into the aphid gut was reduced at night.These data suggest that while diumal variation occurs in phloem sap composition,aphids use night time feeding to overcome the high osmotic stress incurred while feeding on sugar-rich phloem sap during the day.