Crossing experiments and behavioural observations reveal reproductive isolation in two invasive whitefly species

【摘要】：The 'B biotype' and 'Q biotype' of the whitefly Bemisia tabaci(Gennadius)(Hemiptera: Aleyrodidae) have been invading many parts of the world and causing severe damage to a range of crops.Recent phylogenetic analyses suggest that B.tabaci is a species complex containing at least 28 cryptic species,of which the B and Q biotypes belong to the Middle East-Asia Minor 1(hereon MEAM1) and Mediterranean(hereon MED) putative species.Although various attempts have been made to examine the reproductive compatibility between MEAM1 and MED,most of the reports did not present the detailed experimental data,and few studies have tested the fertility of the F1 females,so the extent of possible gene flow between the two genetic groups remains unclear.In this study,we conducted two sets of crossing experiments using populations of MEAM1 and MED collected from different locations in Zhejiang,China,a region recently invaded by these whiteflies.Crossing experiments between the two putative species using either single-pairs or small groups demonstrated that proportions of females in the F1 progeny were only 0-2%in the inter-species crosses compared to 58-68%in the intra-species treatments.Furthermore,all inter-species F1 females were sterile. Meanwhile,we conducted observations on mating behaviour.Continuous video monitoring and recording showed that the adults of different sex from the two putative species very rarely copulated, and copulation occurred only when adults of opposite sex from different putative species were enclosed in dense cohorts for a relatively long period of time.During the behavioural observations,we also compared the mating behaviour of the whitefly on various leaf substrates and found that frequency of mating events on undetached leaves were substantially higher than that on detached leaves, demonstrating the necessity of observing mating behaviour on undetached leaves.Our data show that the populations of MEAM1and MED examined in this study are completely isolated in reproduction and offer new evidence that MEAM1and MED are two well-defined cryptic species.Further,our data indicate that the isolation is due to mainly a copulation barrier,but post-copulation barriers may also be involved.