A Study On The Interspecific Competition Between Brassica Tabaci And Brassica Napus

Myzus persicae（Sulzer）is one of the top ten pests in China,which has the characteristics of short life cycle,large reproduction,long damage time and wide host range.It can harm more than 400 species of plants in more than 50 families and spread115 plant viruses.In nature,parasitic wasps play an important role in controlling the population of M.persicae,in which Aphidius gifuensis Ashmaed and Diaeretiella rapae（M’Intosh）are important unisexual internal parasites of tobacco aphids.When these two kinds of bees are used for compound control at the same time,whether the interspecific competition will occur because they are in the same habitat,so this paper takes A.gifuensis and D.rapae as the research object.the age-stage bisexual life table was used to evaluate the effect of two kinds of parasitoids on the prevention and control of M.persicae,and then clarify the recognition ability and interspecific competition interaction of the two species of parasitoids.The main results and conclusions are as follows:1 Using life table to evaluate the control potential of parasitoid to M.persicae.Taking M.persicae as the host,the population life tables of two kinds of parasitoid and M.persicae were established.Through comparison,the damage control potential of A.gifuensis and D.rapae to M.persicae was further clarified.The results of population parameters were as follows:intrinsic rate of increase（r_m）,net reproduction rate（R₀）and finite rate of increase（λ）of parasitoid were significantly higher than those of M.persicae.The generation time（T）of A.gifuensis（12.60 d）was significantly longer than that of D.rapae（12.12 d）and M.persicae（11.53 d）,but there was no significant difference between the latter two.There was no significant difference among the other parameters,and the net reproduction rate of D.rapae（R₀=93.30）was slightly higher than that of A.gifuensis（R₀=79.38）.It shows that both kinds of parasitoid can effectively control the population growth of M.persicae.2 External competition between A.gifuensis and D.rapae.The external competition mainly occurs in the host search and location and host quality identification by parasitoid.In this experiment,the external competition of the two kinds of parasitoid was studied from the host identification of A.gifuensis and D.rapae.the results showed that the hyperparasitism rate of A.gifuensis self-recognition interval of 0 h,24 h,48 h and 72 h was 66%,52%,14%and 6%,respectively.The longer the interval,the lower the overparasitism.D.rapae self-identification interval 0h,24 h,48 h,72 h hyperparasitism rate of 32%,34%,12%,12%,there is a tendency to avoid overparasitism.The results of intraspecific recognition showed that the hyperparasitism rates of A.gifuensis with spawning interval of 0 h,24 h,48 h and 72 h were 68%,58%,12%and0%,respectively.The hyperparasitism rates of zero spawning interval 0 h,24 h,48 h and 72 h were 68%,60%,18%and 0%,respectively.The parasitic strategies of A.gifuensis without spawning experience were not significantly different,and the parasitic trend was similar to that of spawning experience,and the longer the time interval was,the parasitic phenomenon could be avoided.The hyperparasitism rates of D.rapae with spawning interval of 0 h,24 h,48 h and 72 h were 32%,28%,20%and 0,respectively.The hyperparasitism rates of zero spawning interval 0 h,24 h,48 h and 72 h were 32%,30%,16%and 0%,respectively.At different intervals,D.rapae avoided parasitism,and spawning experience had no significant effect on parasitoid parasitic strategy.The results of conspecific recognition showed that the overparasitism rates of A.gifuensis with spawning intervals of 0 h,24 h,48 h and 72 h were 56%,42%,4%and0%,respectively.The hyperparasitism rates of zero spawning interval 0 h,24 h,48 h and 72 h were 62%,32%,20%and 0%,respectively.The hyperparasitism rates of spawning experiences of D.rapae at intervals of 0 h,24 h,48 h and 72 h were 46%,22%,0%and 0%,respectively.The hyperparasitism rates of zero spawning interval 0h,24 h,48 h and 72 h were 54%,14%,20%and 0%,respectively.The spawning experience had no significant effect on the recognition of A.gifuensis and D.rapae,but was significantly affected by the interval time.A.gifuensis has a certain host recognition effect on parasitic 48 h and 72 h,and the longer the interval is,the stronger the recognition ability is.With regard to D.rapae,except for 0h interspecific recognition,other self-recognition,conspecific recognition and interspecific recognition all showed the phenomenon of avoiding spawning,and the longer the time interval,the more obvious the recognition ability.3 Internal competition between A.gifuensis and D.rapae.The internal competition is mainly manifested in the phenomenon that multiple larvae of parasitoids compete for resources in the same host when there is a lack of host resources.The results showed that when the two parasitoids were treated at the same time,the parasitism rate and emergence rate had no significant change compared with those treated alone,and the numbers of A.gifuensis and D.rapae accounted for half of each other.Under the combined treatment of different parasitic sequence and time interval,the first parasitic parasitoid was dominant,and the number of offspring was significantly higher than that of the latter parasitoid.With the increase of time interval,the effect on the first parasitoid was not obvious,but the effect on the latter parasitoid showed that the number of offspring decreased significantly,and the parasitic rate and emergence rate showed a downward trend.The mortality of parasitoid in different treatments was compared.the results showed that the mortality of parasitoid increased significantly in the interval of 48 h and 72 h,and the offspring of parasitoid were greatly affected.