The Determination Of Effective Accumulatied Temperature And Bio-control Of Semanotus Bifasciatus

Platycdus orientalis,one of the city trees in Beijing,has been demaged by Semanotus bifasciatus. Biocontrol is one of the most important control measures for Semanotus bifasciatus,but there are some problems in biocontrol.For example,Scleroderma guani,an important enemy of many boring pests, whose adults can not survive in winter,must be used every year,so the cost of control is very high. Scleroderma guani prefer to parasite the older hosts and it is hard to determine the appropriate control time;there were a few researches in new enemy pyemotes sp.,we don't know the mechanism of its parastism.Biological missile technology inspired us to use Scleroderma guani which may take Beauveria to control boring pests.In the research,the effective accumulated temperature and developmental threshold temperature were determined.In biological control area,we used Pyemotes as objective to study the mechanism during its parasitism,using Scleroderma guani which can bring the Beauveria to control Semanotus bifasciatus.The main results were as follows.1.Under constant temperatures the value of Ct which is the conmunicated temperature has a range of 8.90±1.77℃and the value of K which is the threshold temperature lies between 95.19±13.14 degree-days for eggs;the values for larvae are Ct=13.26±3.06℃and the number of degree-days K=2,885.07±187.87 degree-days;for pupae the ranges are Ct=17.33±1.24℃and K=131.203±25.634 degree-days.Under the condition of ambient temperatures,the values for eggs are Ct=8.928±2.486℃and K=70.79±8.99 degree-days.It is suggested that S.bifasciatus adults overwinter in a state of dormancy,not at a diapause.It is different with the past reports.2.In the study of the parasitic chracteristics of Pyemotes sp.,the result showed that the parastic time is long when Pyemotes sp.bite the host which has strong reaction affecting the paratism of pyemotes, otherwise,the parasitic time is short.If the young Pyemotes slide from the host,they will have no chance to reparasite.The body size of the hosts had effect on parasitism.In the study,the phenomenon can be found that the body wall of the host can affect the parasitism of the Pyemotes.The harder the body wall is,the weaker the parasitic ability is.3.Under the conditions of the indoor and outdoor experiment,we used Pyemotes sp.to control Semanotus bifasciatus,the results showed that the appropriate control time is from April to May,it can parasite young hosts very easily,average corrected mortality is above 80%;the result of variance analysis shows that there is no significant differences among the released quantities of Pyemotes sp.to control Semanotus bifasciatus.Test for Pyemotes sp.to control different age of hosts,the results showed that there is time-delayed effect for Pyemotes to parasite the host.The Pyemotes is prior to parasite the young hosts,their morality can be 100%in 5 days.For middle larvae,mortality was 95.5%in 8 days. For old age larvae,the mortality was 41.8%.Pyemotes sp.has no selectivity to different instar of hosts, but the older host can affect its parasitism.4.Using Scleroderma guani to control Semanotus bifasciatus,the main results showed that Scleroderma guani tent to parasite middle and older host which have enough nutrition to be used.The appropriate controling time is from Mid-May to early June,the approptiate temperature is about 24℃and the approptiate huminity is 60-70%.Study on behavior of Scleroderma guani showed that it has selectivity to host.5.Using Scleroderma guani carrying Beauveria bassiana to control Semanotus bifasciatus,the main results were as follows:(1) Strains 1-BbFD and strains 2-BtYR were selected from four strains of Beauveria bassiana and they had high toxicity for Semanotus bifasciatus,but they had low toxicity for Scleroderma guani;Strains 2-BtYR had higher toxicity than strain 1-BbFD.(2) There are positive relationship between pathogenicity of Beauveria bassiana and bacilli concentration.(3) Scleroderma guani carries certain concentration of Beauveria to control larvae of Semanotus bifasciatus,the pests mortality increased when increasing the ratio of Scleroderma guani vs insects,the pests have highest mortality in ratio 3:1(4) Considering the duoble factors,the ratio of Scleroderma guani vs hosts and the different concentration of Beauveria,high ratio of Scleroderma guani vs hosts and intermediate-state concentration of bacteria can cause the highest fatality rate of the pests.