Effects Of Parental Experience On Diapause Incidence Of Offspring In Microplitis Mediator (Haliday) (Hymenoptera: Braconidae)

The solitary larval endoparasitoid Microplitis mediator is a Palaearctic species widelydistributed in Europe and Asia, which parasitizes larvae of about 40 different lepidopteranspecies and is the dominant parasitoid of Helicoverpa armigera (Hübner) in China. Previousstudies suggested that M. mediator exhibited a facultative diapause and entered diapauseduring the pupae stage when the average temperature was below 20°C and the day length wasshorter than 12 h. A naturally occurring pupal diapause in M. mediator may be useful tosynchronize large-scale production of the parasitoid if the onset and termination of diapausecan be controlled through rearing conditions.In many insects, diapause is influenced by the environmental conditions experienced bythe parental generation. Female that experience short-day conditions, low temperatures tendto produce a high proportion diapause offspring. However, the parental effects of photoperiodand temperature have not yet been examined in M. mediator. In the present study, the effectsof four different parental experiences on diapause incidence of offspring were examined in M.mediator.1. The diapause incidence of offspring in M.mediator was evaluated in the laboratory byexposing mother generation to different conditions including 7 different photoperiods ( 0h∶24 h, 4 h∶20 h, 8 h∶16 h, 12 h∶12 h, 16 h∶8 h, 20 h∶4 h, 24 h∶0 h ) at 23℃,Theoffspring were exposed to 3 photoperiods (10 h∶14 h, 12 h∶12 h, 14 h∶10 h) at 3temperatures (16℃, 20℃, 24℃). The results indicated that the different experiencedphotoperiod on the parental generation of the M. mediator had significant influence ondiapause incidence of the offspring; the interaction of temperature and photoperiod couldaffect the occurrence of the diapause and the parental photoperiod and temperature experiencehad significant influence on diapause incidence of the offspring.2. The diapause incidence of offspring in M. mediator was evaluated in the laboratory byexposing M. mediator to different conditions including 3 photoperiods (10 h∶14 h, 12 h∶12h, 14 h∶10 h) crossed 3 temperatures (16℃, 20℃, 24℃), The offspring were exposed to 3photoperiods (10 h∶14 h, 12 h∶12 h, 14 h∶10 h) at 3 temperatures (16℃, 20℃, 24℃). Theresults indicated that the interaction of temperature and photoperiod could affect theoccurrence of the diapause and the parental photoperiod and temperature experience hadsignificant influence on diapause incidence of the offspring. 3. The diapause incidence of offspring in M. mediator was evaluated in the laboratory byusing the different day-old mated adults emerged from the diapause cocoons and thedeveloping cocoons, The offspring were exposed to 3 photoperiods (10 h∶14 h, 12 h∶12 h,14 h∶10 h) at 3 temperatures (16℃, 20℃, 24℃). The results indicated that the differentday-old mated adults had no significant effect on the diapause incidence of their offspring.4. The diapause incidence of offspring in M. mediator was evaluated in the laboratory byusing the reciprocal hybridizations were made with the adults which emergence from thediapause cocoons and the adults which emergence from the developing cocoons. Thereafter,exposing their offspring to 3 photoperiod regimes (10L:14D,12L:12D,14L:10D) with 3temperatures (16,20,24℃). The results indicated that the hybridization of the parents caneffect the diapause rate of their offspring significantly and the interaction of the temperatureand the photoperiod can effect the incidence of the diapauses; the diapause incidence of the M.mediator may be related to the maternal gene, but the offspring whether enter diapause or nostill rely on the effects of the photoperiod and temperature conditions.Our results suggest that the parental experience may play an important role in thediapause induction of their progeny, but the interaction of multiple factors, including geneticand environmental factors might also control the incidence of diapause.