Influencing Factors For Parasitism And Reproduction Of Sclerodermus Alternatusi Yang

Sclerodermus alternatusi is an ectoparasitoid of the larvae of Monochamus alternatus.The parasitoid has a strong control effect on hosts and broad application prospects in biological control.In order to improve the control efficiency of S.alternatusi,in this experiment,the larvae of Thyestilla gebleri were used as the alternative host,mainly studied that how the foundress number,temperature,cold storage time and host size affect performance of S.alternatusi and its progeny.Some parasitism parameters were compared,and the developmental threshold temperature and effective accumulated temperature were also calculated.So that we can clarify the influence of the above four factors on the performance of S.alternatusi,and provide theoretical supports for artificial rearing of parasitoid and biological control utilization in practice.The main results of this study are as follows:1.The foundresses number can affect the performance of S.alternatusi and its progenies.In present study,every group alternative hosts were inoculated with one to six foundresses per host,respectively,then placed them in an artificial climate box.The results showed that for the maternal parasitoids,the time to first attack,paralysis time,and pre-oviposition period were shortened as the foundresses number increased.For the progenies,the larval stage shortened with the increase of the foundresses number,but did not affect the egg stage and the pupal stage.The number of progenies increased firstly and then decreased as the foundresses number increased.When the density was 5 parasitoids per host,the number of progenies was the largest.The sex ratio of offspring was a bias-female ratio and had positive correlation with the foundresses number.What's more,the percentage of winged females decreased with the increase of the foundresses number.2.The proper rearing temperature can improve the reproduction and development of S.alternatusi.However,once the temperature is over the optimum threshold,parasitism of maternal parasitoids and development of progenies will be adversely affected.Parasitoids were artificially reared artificially at different constant temperatures(21,24,27,30,33 ?)under laboratory conditions.Developmental duration of each stage and the progeny number were recorded.The developmental threshold temperature and effective accumulated temperature were also calculated by using the least squares method.The results showed that the developmental durations of S.alternatusi were negative relation with temperature.The developmental threshold temperatures for egg,larva,pupa were 6.99 ± 2.12,10.67 ± 3.43 and 13.5 ± 2.71 ?,while the effective accumulated temperatures were 49.28 ± 5.08,166.67 ± 34.02 and 225±43.30 degreeday respectively.The temperature also showed significant effects on the number and sex ratio of the progenies.As the rearing temperature exceeded 30 °C,the number and male proportion of the progenies decreased significantly.3.The performance of S.alternatusi decreased with the increase of cold storge duration.In this experiment,the newly emerged parasitoids were placed in an artificial climate chamber at 8 °C,and stored for 30,60,90,and 120 d,respectively,and some parasitism fitness parameters of S.alternatusin were analyzed.,such as the survival rate,parasitism rate.The results showed that the time that parasitoids were exposured in the low temperature environment was longer,the lower the survival rate of S.alternatusin,the smaller the number of progenies,and the higher the proportion of male in the offspring.4.The host size can affect the oviposition decision of S.alternatusi,and the parasitoids can adjust the fitness according to the host quality.Parasitoids were artificially reared at different host size(0.10?0.15 g,0.15?0.20 g,0.20?0.25 g,0.25?0.30 g,0.30?0.35 g)of T.gebleri under laboratory conditions.The parasitism and oviposition behaviors were observed and the progeny number and sex ratio were recorded.The results showed that host size did not affect the parasitism rate of S.alternatusi.And the progeny fitness was affected by host size,as follows: host size had no effect on the parasitism rate,the progeny number were positive relation with host size,the male proportion of progeny declined as the increased of host size.