Competitive Displacement Between The B Biotype And ZHJ2 Biotype Of The Whitefly Bemisia Tabaci On Kidneybean

The B biotype of the whitefly Bemisia tabaci(Gennadius)(Hemiptera:Aleyrodidae) is a major pest of both greenhouse and open-field crops worldwide.It has caused extensive ciop damage and economic loss through phloem feeding,excretion of honeydew,induction of phytotoxic disorders,and transmission of plant viruses since it invaded into China in late 1990s.Extensive field data showed that the B biotype has gradually displaced some indigenous biotypes of this species complex in many regions of invasion.In addition, laboratory studies have shown that the B biotype has the capacity to replace the native biotypes(ZHJ1 and ZHJ2 biotypes) in Zhejiang province in a short period of time.The B biotype of B.tabaci has a much wider range of host plants than that of many indigenous biotypes,and the suitability of the same plant to the whitefly may also differ between the B biotype and indigenous biotypes.In previous studies,only host plants that showed similar levels of suitability to both the B biotype and the indigenous biotypes or relatively higher levels of suitability to the B biotype were used in various competition experiemtns.It is not known whether the B biotype can displace an indigenious biotype when they co-occur on a host plant that is relatively more suitable to the indigenious biotype.Therefore,in this study,we used kidneybean,a host plant that showed a relatively higher level of suitability to the ZHJ2 biotype than to the B biotype,to initiate mixed populations of these two biotypes and follow up the changes of relative proportion of the two biotypes.Our objective was to further investigate the potential capacity of the B biotype to displace indigenious biotypes of the whitefly.The results are summarized as follows:(1) Comparison of performance of the B biotype and ZHJ2 biotype on two host paintsThe adult longevity,fecundity,survival rate of immature stages and development time of the B biotype and ZHJ2 biotype were compared on cotton and kidneybean.The results showed that cotton was a suitable host plant for both biotypes,while kidneybean showed a significantly higher level of suitability to the ZHJ2 biotype than to the B biotype.(2) Competitive displacement between the B biotype and ZHJ2 biotype on kidneybeanThe mixed cohorts began competition with 50%B and 50%ZHJ2.Every 25 days adults were collected from the mix population for sex determination and biotyping.The results showed that,although the proportion of the B biotype in the first three generations was lower than the initial ratio of this biotype(50%),it began to rise thereafter and reached to 58.7%at the 4^th generation and 98.2%at 8^th generation.By the 10^th generation,the ZHJ2 biotype was completely displaced by the B biotype.These results demonstrate for the first time that the B biotype of B.tabaci can displace indigenous B.tabaci through competition even on a host plant that is less suitable to the B biotype.Major new findings of this study:We found that under laboratory caged conditions the B biotype of B.tabaci had the capacity to displace the indigenous ZHJ2 biotype in a short period of time on a host plant that is less suitable to the B than to the indigenous biotype.