Studies On The Rearing Technique And Host Selection Behaviors Of Spathius Agrili Yang

Spathius agrili Yang(Hymenoptera:Braconidae) is an important ectoparasitic wasp of the Agrilus planipennis Fairmaire(Coleoptera:Buprestidae) larvae.This parasitoid has the potential to use as an excellent biological control agent for suppressing populations of its host. In order to utilize this natural enemy,the mass rearing techniques,Effects of temperature on development and reproduction ofS.agrili,Sphenoptera sp.was used as a host for rearing of S. agrili and the inundative release experiments were conducted in field were mainly studied. This article studied the responses of S.agrili to volatiles by chemical ecology and behavior ecology to find the role of phytochemicals in host-finding of S.agrili.The main results are summarized as follows.The study on the growth,development and reproduction of S.agrili at 6 differernt temperatures(22℃,24℃,26℃,28℃,30℃,32℃).The results showed that the developmental rate of egg,pupa and the whole generation of Spathius agrili yang increased with the rise of temperature from 22℃to 32℃,but the developmental rate of larva was highest at 26℃.The developmental threshold temperature required for egg,larva,pupa and whole generation was 14.34℃,16.89℃,14.16℃and 13.84℃,while the effective accumulated temperature was 24.59,61.16,166.27 and 276.80 degree_day,respectively.Temperature had different level effects on parasitic rate,the rate of successful parasitism,egg number,number of generations and sex ratio of S.agrili.The results showed that the temperature from 26℃to 28℃was suitable for the development and reproduction of S.agrili.This experiment designed five inoculating ways to mass rearing with stem-way,timber-way and wraped paper-way successfully reproducing the wasp.The parasitic rate was the largest when employing timber-way,reaching up to 87.50%and the average egg number was 6.14.The advantage of this way was less work;the parasitic rate was much lower in wraped paper-way which could not meet the requirement for reproducing parasitoids.After comparing these ways,the operation of stem-way was more simple and less labourious which was fit for mass rearing but the parasitic rate was relatively lower,in comparision with timber-way,and needed more improvement.Screening substitute hosts was a key factor in the process of mass rearing.This experiment has selected some larvaes of wood borers from parasitoid's natural surroundings and the larvae of Bupresidae to mass rearing.The rescult shows that Sphenoptera sp.could be successfully parasitized by S.agrili.To explore the possibility for S.agrili manage the A.planipennis,the field release was conducted.The parasitic rate was 15.38%before releasing parasitoid in the field.The parasitic rate was 53.85%next April which witnessed a remarkable increase in parasitic rate while the parasitic rate maintained above 46.15%,showing a huge effect.The female's behaviour was investigated by Y-tube olfactometer.The results indicated different volatile had such attraction to wasp that the leaves attracted by host＞healthy leaves= the bark attracted by host＞healthy bark＞host larvae＞frass,and the parasitoid showed preferences to the leaves attracted by host(p＜0.05) while there was no preferences to healthy leaves(p＞0.05),this indicated that the choice for hosts' residents of S.agrili mainly depended on the information given out by the leaves attracted by host.This information might come from plants' volatiles induced by pests and have something to with the cooperative effect between host plants and pest injury.EAG was used to test the S.agrili's antenna EAG response to four kinds source of volatiles and the results showed the relative value of EAG response to four kinds source was as follows:the leaves attracted by host＞frass＞the bark attracted by host＞host larvae.The rescults also showed the significant EAG responses difference between the leaves attracted by host and blank,while between leaves attracted by host and host larvae(P＜0.05).These results in this experiment were coherent with the results of Y-tube olfactometer.Antennae and their sensilla of S.agrili were observed using scanning electron microscopy. Both sexes of antenae were threadlike.Five types of sensilla were found on the antennae of female.They are sensilla trichodea,sensilla chaetica,sensilla placodea,sensilla basiconca and sensilla campaniformia,respectively.But only there types of sensilla were found on the antennae of male.The difference between sexes mainly related to the unique behaviour of females and males,so it could be presumed that sensilla basiconca and sensilla campaniformia play a greatly important role in host location.