Wing Dimorphism And Parasitic Fitness Of Sclerodermus Pupariae(Hymenoptera: Bethylidae)

The gregarious idiobiont ectoprarasitoid,Sclerodermus pupariae Yang et Yao?Hymenoptera:Bethylidae?,is a newly described species from Tianjin,China,parasitizing emerald ash borer?EAB?,Agrilus planipennis Fairmaire?Coleoptera:Buprestidae?.Laboratory studies indicate that this parasitoid can also paralyze and kill larvae of many species of Cerambycidae and Buprestidae.It has been widely used as an effective biological control agent against wood-boring forest pests.Both winged and wingless female morphs of S.pupariae can find and parasitize hosts;however,winged parasitoids can disperse faster and further to new habitats and thus are more adaptive to spatial and temporal changes in host densities than wingless morphs.In order to increase the efficacy of biological control programs and supplement current protocols for mass-rearing of S.pupariae,the effects of environmental factors on the wing dimorphism and parasitism fitness were determined,as well as the difference of gene expression between winged and wingless female adults of S.pupariae.The results were showed as follows:1.Rearing temperature could realize regulation of wing morphs and affect progeny fitness significantly.Winged female proportions of S.pupariae reared under 27°C and 30°C reached62%and 68%respectively and were significantly higher than other temperatures.The lowest was only 0.97%under 24°C and it was regareded as the wingless temperature?Twl?.The parasitism rate and successful parasitism rate increased with the rise of temperature.Sclerodermus pupariae maintained the highest parasitism rate of 100%at 30°C and the highest successful parasitism rate of 93.3%at 27°C and 30°C,and both decreased to 73.3%and 60%respectively when temperature was over 30°C.The brood size significantly increased from 58at 21°C to 91.1 at 30°C and declined sharply to 52.5 in average when the temperature was over30°C.The pre-oviposition duration shortened while the developmental rate of larva,pupa and the entire immature stages of S.pupariae increased with the rise of temperature from 21°C to33°C,but the highest developmental rate of egg was at 27°C.The suitable temperature for artificial rearing of S.pupariae ranges from 27°C to 30°C.2.Significantly more winged female parasitoid progeny were produced with long-day photoperiods?16h?and high light intensity compared to short day-photoperiods?8h?and low light intensity treatments.Photoperiod alone?regardless of light intensity?has significant impact on developmental time of parasitoid progeny.Light intensity,interacted with photoperiod,significantly affected the degree of phenotypic partitioning and development time,but light intensity and photoperiod did not significantly influence the parasitoid fecundity and sex ratio.3.Sclerodermus pupariae maintained high fitness after cold storage under 8°C,and the winged female proportion decreased as the storage time.The parasitic fitness of parasitoid decreased after cold storage for 2 months.When the storage time was 1 month,pre-oviposition period and immature period extended,although there was no significant difference in progeny number,winged female proportion and sex ratio.When the storage time increased to 2 months,progeny number significantly decreased and pre-oviposition period increased further which delayed about 5 days compared to the control.In addition,the winged female proportion decreased significantly while sex ratio increased.In general,parasitism rates and successful parasitism rates of female parasitoid both were high after cold storage for 2 months.It suggests that cold storage for less than 2 months is acceptable before field release for the parasitoid in biological control programs.4.Exogenous precocene II could increase winged female proportion of S.pupariae,however ecdyterone had no effects on development of wing morphs of this parasitoid.PII treated hosts under Twl could increase winged female proportion,significantly higher than control?2.6%?.Wing dimorphism differed among different ages of parasitoid larvae.Winged female proportion of larvae parasitoid on the 3^rd,5^th and 7^th day treated by PII were significantly higher than the control,whereas on the 1^st day did not significantly changed.We proved that the sensitive period for wing dimorphism was in the late larval development stage of parasitoid.5.Wing polyphenism in various sister broods of S.pupariae may reflect adaptive reproductive strategy.The parasitism ability on host larvae and brood sizes reduced gradually.The percentage of winged females decreased with the number of produced sister broods,along with the most dramatic decrease in the third sister brood.The sex ratio of progeny showed a parabolic trend at various successive sister broods and it was close to 1:1 for the third sister brood.The growth and development of progeny has significant difference in various successive sister broods of Spupariae.The population type of S.pupariae progeny completes the transition from dispersal-reproduction to reproduction only as a result of decreasing in percentage of winged female at sister broods of this parasitoid.The production of the third sister brood might be a key point for regulating wing morph and sex ratio of progeny to maximize the fitness of the population in the lifetime in S.pupariae.6.The transcriptomic differences between winged and wingless of female adults of S.pupariae indicated that there were 12 different expression genes in the two morphs of this parasitoid.Those genes related to muscle and energy were highly expressed in winged female,which resulted from the demand to disperse to seek hosts and synthesis of flight muscle was closely related to the flight ability.In addition,the high expression of genes related to energy metabolism suggested that winged female allocate more energy for flight.Troponin was the most highly expression genes among the 12 up-regulated genes.These genes might play an important role in the formation of flight muscle,which suggested the flight traits in S.pupariae on the other side.In the present study,the effect of environmental factors including temperature,light condition and cold storage on the wing dimorphism were investigated and the parasitism fitness of parasitoid under different environments were explored.These results provide theoretical basis for improving the efficiency of biological control by increasing the winged female proportion of S.pupariae.