Effects of mummy consumption on fitness and oviposition site selection on Harmonia axyridis

Intraguild predation(IGP)has been commonly reported between predators and parasitoids used as biological control agents as predators consuming parasitoids within their hosts.However,the effect of parasitoid-mummy consumption on the fitness of the predator and subsequent oviposition site selection have not been well studied.In our study,we conducted two laboratory experiments to examine the influence of Aphidius gifuen-sis Ashmead(Hymenoptera:Braconidae)mummies as prey on fitness and subsequently oviposition site selection of Harmonia axyridis(Pallas)(Coleoptera:Coccnellidae).Re-sults indicate that when H.aryridis was reared on A.gifiuensis mummies only,its larval development was prolonged,and body weight of the 4th instar larvae and newly emerged adults,and fecundity decreased.Moreover,H.axyridis did not exhibit oviposition pref-erence on plants infested with unparasitized aphids or aphids parasitized for shorter than 9 days.However,compared with plants with mummies(parasitized≥9 days),H.axryridis laid more eggs on plants with unparasitized aphids.In contrast,H.axryridis previously fed with A.gifuensis mummies did not show a significant oviposition preference between plants with unparasitized aphids and those with mummies(parasitized≥9 days).Overall,our results suggest that mummy consumption reduced the fitness of H.axyridis.Although H.axyridis avoided laying eggs on plants with A.gifuensis mummies,prior feeding ex-perience on A.gifuensis mummies could alter the oviposition site preference.Thus,in biological control practice,prior feeding experience of H.axyridis should be carflly considered for reduction of IGP and increase of fitness of H.axyridis on A.gifuensis.

Aspartate-β-alanine-NBAD pathway regulates pupal melanin pigmentation plasticity of ladybird Harmonia axyridis

Phenotypic plasticity is observed in many animal species and it is effective for them to cope with many types of environmental threats.The multicolored Asian ladybird Harmonia axyridis shows a cuticular pigmentation plasticity that can be rapidly induced by temperature changes,and in the form of changeable melanin spot patterns to adjust heat-absorbing.Here,H.axyridis with thermal stimulation were selected for determining the molecular regulations behind it.First,we confirmed the melanin level changes of H.axyridis pupa could be induced by temperature,and then screened the efficient time window for thermal sensing of H.axyridis pre-pupa;it is suggested that the late stage of pre-pupa(late stage of 4th instar larva)is the critical period to sense thermal signals and adjust its pupal melanin spot area size to adapt to upcoming thermal conditions.The Ha-ADC(aspartate decarboxylase)and Ha-ebony(NBAD synthase)of aspartate-β-alanine-NBAD pathway were then proved in regulation of cuticular melanization for pupa through RNA interference experiments;knockdown of these two genes enlarged the melanin spot size.Finally,we designed a random injection of Ha-ADC at different pre-pupal stages,to further study the regulation window during this process.Combined with all evidence observed,we suggested the spot size determination can be regulated very close to the time point of pupation,and genes of the aspartate-β-alanine-NBAD pathway play an important role at the molecular level.In brief,H.axyridis exhibits a flexible active physiological regulation through transcriptional modification to thermal changes.

Abdominal-B regulates structure and development of the Harmonia axyridis cremaster

The ladybird Harmonia axyridis is an insect that exhibits pupal attachment to plants,which facilitates development and environmental adaptation.The cremaster is highly specialized for this behavior.However,the underlying molecular regulation of the cremaster remains unclear;therefore,we performed experiments to investigate the transcriptional regulation of cremaster development.First,we examined the morphological structure of the cremaster to reveal its function in pupal attachment of H.axyridis.Next,we analyzed the Hox gene Ha-Abd-B using RNA interference(RNAi)to determine its function in regulating cremaster formation;Ha-Abd-B up-regulation promoted effective pupal attachment,whereas successful RNAi caused severe down-regulation of this gene,and pupae were unable to attach.Furthermore,successful RNAi and subsequent Ha-Abd-B down-regulation caused phenotypic changes in cremaster structure,including its complete disappearance from some individuals.Finally,we observed unique development of the cremaster and dynamic expression of Ha-Abd-B during pre-pupal development;consequently,we hypothesized that there was specific pre-pupal development of the cremaster.Overall,based on these results,the specialized cremasteric structure located on the posterior side of H.axyridis was determined to be a key organ for pupal attachment.Cremaster identification in H.axyridis is regulated by Ha-Abd-B and exhibits preferential development.Pupal attachment of H.axyridis reveals an environmental adaptation of this species;thus,this study and future molecular studies will help determine the role of Hox genes in regulation of insect attachment and further our understanding of the multiple functions of Hox genes.