Investigation Of Phytoseiid Mites In Beijing And An Evaluation Of The Control Ability Of Neoseiulus Barkeri On Western Flower Thrips

Frankliniella occidentalis(Pergande),western flower thrips(WFT),originating from the Rocky Mountains of western United States had spread throughout the North America in the 1970s and 1980s.WFT was firstly considered to be a greenhouse pest in Alberta of Canada in 1983 and up to now it has distributed in more than 69 countries or regions.It was defined as a quarantine pest in 1996 in China.Not long it was discovered in greenhouses of a suburb of Beijing in 2003 and caused serious symptoms,additionally,it was also discovered in Yunnan and Guizhou provinces.WFT is highly possible to outbreak in wider areas.As it is strongly resistance to pesticides and often hidden in the crevice and folds of plant organs,the chemical control measures have poor effect with high costs.Therefore,alternative methods such as using natural enemies to control the WFT have been drawing more and more attention of agricultural scientists.Predatory mites are important natural enemies of thrips,among which Neoseiulus barkeri and N.cucumeris have been applied in large scales in developed nations.The former species was widely distributed in China and the second one was introduced from England to China in 1997,and both have been commercialized for spider mites control,however,the researches on the usage of N.barkeri on the control of thrips have rarely been reported.In order to understanding the resources of predatory mites and find potential natural enemies of WFT,we conducted a survey on the Phytoseiidae species in Beijing and carried out experiments on life table of N.barkeri feed on WFT.Numerical response and functional response of N.barkeri to WFT were studied and the control ability of N.barkeri fed on WFT was compared with N. cucumeris.The results are as follows:(1)Twenty eight species belonging to 9 genera and 3 subfamilies of Phytoseiidae were collected and identified--Amblyseiinae:5 genera,17 species;Typhlodrominae: 3 genera,7 species;Phytoseiiane:1 genera 4 species.(2)The average durations of egg,larva,pronymph and deunymph of N.barkeri preying on WFT were 1.93±0.27,0.63±0.25,1.80±0.63 and 1.37±0.56 days, respectively.The intrinsic rate of pupolation increase(r_m)was 0.15 and the net reproductive rates(R₀)was 27.37.The generation time(T),innate capacity for increase(λ)and the doubling time(t)were 22.17 days,1.16 and 4.64 days, respectively.(3)The development and the reproduction of N.barkeri were both affected by the number of the 1^stinstar larvae of WFT.The reproduction and longevity of females increased when the number of prey added.Larvae of N.barkeri could successively developed to adults on a density of 1,3,5,7 and 9 WFT.The life expectancy and reproduction of N.barkeri reached the standards when prey density was higher than 7.(4)The functional equations of N.barkeri and N.cucumeris preying on WFT were Na = 0.5391×N₀ /(1×N₀ +0.0437)and Na = 1.0799×N₀ /(1×N₀ +0.1069) and the largest prey number consumed was 12 and 10,respectively.The predation of the two predators were significantly different under the prey densities of 5,10,20 and 30,however,it was not the case when the density increased to 40 and 50.The high intrinsic rate of pupolation increase and the short population doubling time of N.barkeri indicates that N.barkeri is an efficient predator of WFT.To establish a stable population of N.barkeri a release rate of 1 predator to 7 WFT should be considered.Both N.barkeri and N.cucumeris provided a sound control result on the WFT when the density of the thrips was high.The WFT population was obviously suppressed when the reproduction of N.barkeri was increased.