The Interspecific Competition Between Frankliniella Occidentalis (Perganda) And Megalurothrips Usitatus (Bagrall) Under Laboratory Conditions

The western flower thrips Frankliniella occidentalis（Pergande）,has spread to many provinces and areas in China since it invaded into our country in 2003.It not only has caused major economic losses to China’s agriculture,but also it might cause serious threats to biodiversity due to its strong competitiveness in China.Megalurothrips usitatus（Bagrall）is the dominant pest on leguminous crops in China,and it has caused serious damage to the cowpea industry in Hainan Province.In recent years,both species have been found to be harmful to leguminous plants in the suburbs of Guiyang.In order to clarify the interspecific competition between the invasive thrips and native thrips,the competition and displacement between F.occidentalis and M.usitatus on kidney bean and cowpea were studied with or without the stress of abamectin.The reproductive competition of the two thrips were also studied.Besides,the prey preferences and the functional predatory response of Amblyseius swirskii to nymphs of F.occidentalis and M.usitatus was evaluated.The results were as follows:1.Interspecific competition between Frankliniella occidentalis and Megalurothrips usitatus on kidney bean and cowpea podsThe interspecies competitions between F.occidentalis and M.usitatus on kidney bean and cowpea pods with different population ratios were studied.The results showed that M.usitatus population growth was faster than F.occidentalis in the single population at the initial population of 40 thrips.for three consecutive generations on kidney bean pods.When F.occidentalis and M.usitatus coexisted at the initial population rates of 25:15 and 20:20 on kidney bean pods,F.occidentalis displaced M.usitatus after one and two generations,respectively.When F.occidentalis and M.usitatus coexisted at the initial population rates of 15:20 on kidney bean pods,M.usitatus displaced F.occidentalis after three generations.When F.occidentalis and M.usitatus were reared separately on cowpea pods,the population of F.occidentalis could not establish and was almost extinct in the second generation.No matter what ratio of the two thrips coexisted with competiton,M.usitatus replaced F.occidentalis in the first generation.The results of the competition showed that F.occidentalis was more dominant,while M.usitatus was dominant on cowpea pod.The competition between the two thrips indicated that the result of competition was related to the initial population,the species of thrips and host.2.Interspecific competition between Frankliniella occidentalis and Megalurothrips usitatus on kidney bean pods under the stress of abamectinThe interspecific competition between F.occidentalis and M.usitatus on kidney bean pods was studied under avermectin stress.When both species coexisted at the initial population rates of 20:20 on kidney bean pods treated by pesticide.F.occidentalis displaced M.usitatus after one generation,while F.occidentalis need two generations to displace M.usitatus without pesticide treatment.The activities of P450in F.occidentalis was significantly higher than that of the control at all time points.The activities of P450 in M.usitatus was significantly higher than the control at 24 h,48 h,and 72 h,but the enzyme activity in F₁ generation was lower than the control.c DNA fragments of CYP6-3 in M.usitatus were cloned by RT-PCR.The m RNA expression of CYP6-3 in 2nd instar nymphs of two thrips were determined by real-time q PCR at 24h,48 h,72 h and F₁ generation.The m RNA expression of F.occidentalis was significantly down-regulated at 24 h,48 h,and F₁ generation under avermectin stress,while it was significantly up-regulated at 72 h.The m RNA expression of M.usitatus was significantly down-regulated at 24 h,48 h,and 72 h,while it was significantly up-regulated at F₁ generation.The results showed that F.occidentalis might have stronger metabolic resistance under avermectin stress,which accelerated the replacement to M.usitatus.3.The reproductive competition between Frankliniella occidentalis and Megalurothrips usitatusThe changes of fecundity of one thrip at parthenogenetic and bisexual reproduction under the interference of F.occidentalis or M.usitatus were studied by leaf disc tests method.The results showed that the amounts of daily and total fecundity of the two thrips decreased significantly with the increase of female and male adults of the different species at two reproductive modes.And there were significant differences among different treatments.The daily fecundities of M.usitatu at parthenogenetic and bisexual reproduction decreased significantly under the interference of 1 female adult of F.occidentalis,from 8.8 eggs and 6.6 eggs to 4.7 eggs and 2.8 eggs,respectively.The daily fecundities of F.occidentalis at two reproductive modes also decreased significantly under the interference of 1 female adult of M.usitatu,from 6.8 eggs and6.1 eggs to 3.2 eggs and 1.6 eggs,respectively.The daily fecundity of M.usitatu at parthenogenetic decreased significantly under the interference of 2 male adults of F.occidentalis.The daily fecundity of F.occidentalis at bisexual reproduction decreased significantly under the interference of 2 male adults of M.usitatu.The effect of the same number of female adults on fecundity were greater than that of the same number of male adults.The daily and total fecundities of M.usitatus at two reproductive modes were higher than that of the F.occidentalis no matter interfered or not.The results indicated that M.usitatu had a dominant position because of its high fecundity in the reproductive competition with F.occidentalis.4.The prey preferences and the Predation differences of Amblyseius swirskii to Frankliniella occidentalis and Megalurothrips usitatus nymphsThe prey preferences and functional and interference responses of A.swirskii to nymphs of F.occidentalis and M.usitatus were measured at 25℃and 75%RH under laboratory conditions.A.swirskii preferred 1st instar nymphs of both F.occidentalis or M.usitatus to 2nd instar nymphs of these species.There was no difference in its predatory capacity or preference for 1st instar nymphs of either species.However,A.swirskii preferred 2nd instar nymphs of F.occidentalis to those of M.usitatus.The functional responses were good fit to the HollingⅡequations.The predation rate of A.swirskii on 1st instar nymphs decreased with predator densities.The predatory capacities of A.swirskii were affected by the species,developmental stage of its prey and predator density.