Behavioural Mechanisms Underlying The Displacement Of Indigenous Biotypes By The Invasive B Biotype Of Bemisia Tabaci

The B biotype of Bemisia tabaci has spread to much of the rest of the world from its presumed origin in the Mediterranean-Asia Minor-North Africa in the past 20 years and has displaced some indigenous biotypes of this species in the regions of invasion. During the processes of invasion and displacement,the B biotype has caused considerable damage to a range of crops.Revealing the mechanisms underlying the displacement of indigenous biotypes by the B biotype will contribute to explain why the B biotype has such a strong capacity to invade and displace indigenous biotypes, which can provide us with critical theoretical bases to predict whether the B biotype can spread further and displace other indigenous biotypes.This research is aimed to find out the potential of the B biotype to displace the indigenous ZHJ2 biotype and its underlying behavioural mechanisms,and in addition,to study the behavioural mechanisms underlying the displacement of indigenous biotypes ZHJ1 and AN by the B biotype,based on the previous findings from our laboratory that the B biotype could displace indigenous biotypes ZHJ1 and AN.The results are summarized as follows:(1) Observing and recording copulation events of whiteflies on plants using a video cameraA cost-effective,efficient,and reliable video recording system for observing and recording the mating behaviour of whitefly on live plants was developed.With this novel method,a large number of accurate and continuous recordings of courting and mating behaviour of this insect on live plants could be made under more natural condition,and the mating interactions between biotypes of B.tabaci could be observed in detail.(2) Diurnal patterns of adult emergence,pre-copulation intervals and copulation frequencies of biotypes B,ZHJ1 and ZHJ2In biotypes B and ZHJ1,the peak of emergence occurred during the first 2 h of the photophase and in biotype ZHJ2,it occurred during the first 4 h of the photophase. The percentage of females remained 50-60%during the peaks of emergence.In these three biotypes,over 90%of the adults emerged during the first 6 h of the photophase, throughout which the percentage of females remained approximately 60%,and only small proportions of the adults emerged during the scotophase. Continuous observations using the video recording system showed that in the three biotypes,the earliest copulation events occurred 2-6 h after emergence and 56-73%of females copulated at least once by 12 h after emergence.Both females and males copulated multiple times over the first three days.Most of the copulation events occurred during the photophase,while approximately one-fifth of the events occurred during the scotophase.(3) Reproductive compatibility between biotypes B and ZHJ2When adults of biotypes B and ZHJ2 were placed in one arena,mating could occur between the two biotypes.However,the number of events and frequency of copulation between the biotype B and ZHJ2 decreased significantly compared with those between females and males of a given biotype being placed in one arena, demonstrating a degree of pre-mating partial reproductive isolation between these two biotypes.Although some of the adults of the biotype B and ZHJ2 copulated with each other,mated females produced only male progeny,demonstrating a post-mating complete isolation in reproduction between the two biotypes in cases where copulation has happened.Thus,both pre-mating partial reproductive isolation and post-mating complete reproductive isolation existed between these two biotypes.(4) Competitive displacement between biotypes B and ZHJ2 on cottonThe mixed cohorts began with 13%B and 87%ZHJ2,and 50%females.In the treatment without insecticide application,the B biotype had totally displaced ZHJ2 by the sixth generation.During the process of competition and displacement,the female ratio of B increased,while that of ZHJ2 decreased with time.In the treatment where the insecticide imidacloprid was applied after the second generation,the B biotype had totally displaced ZHJ2 by the fifth generation,and during the process of competition and displacement,the female ratio of B increased,while that of ZHJ2 decreased.In cohorts with ZHJ2 only,the female ratio remained at 50%or so throughout.(5) Behavirouai mechanisms underlying the displacement of the indigenous biotype ZHJ2 by the B biotypeDetailed analysis of mating behaviour revealed asymmetric mating interactions between biotypes B and ZHJ2.The B biotype had higher sexual activity than the ZHJ2 biotype in that B females were more receptive to males,and B males more frequently and efficiently courted female of B or ZHJ2.Besides,B males interfered more intensely with courtship initiated by rival males of another biotype than did ZHJ2.B males interfered more successfully with courtships initiated by rival males of ZHJ2 than by males of the same biotype.In contrast,ZHJ2 males interfered more successfully with courtships initiated by males of the same biotype than those initiated by B males.B males could guard females post copulation,and more effectively inhibited courtships from a ZHJ2 male than from a B male during guarding.However, ZHJ2 males separated from females post copulation so that another male had access to court the female.All these behavioural differences between the two biotypes had the consequences that copulation events between B males and females increased in the presence of ZHJ2,while copulation events between ZHJ2 males and females decreased in the presence of B.Also,in the presence of rival males of another biotype, female ratio in the offspring of the B biotype increased while female ratio in the offspring of the ZHJ2 biotype decreased.Copulation duration within the biotype B or ZHJ2 was not influenced by the presence of another male of either biotype,and reproduction of females was not affected by mating between the two biotypes when males of the two biotypes were available.Therefore,we can conclude that as the consequence of asymmetric mating interactions between biotypes B and ZHJ2, asymmetric change of copulation events resulted in the increase of female offspring of the B biotype and decrease of female production of the ZHJ2 biotype.Our data demonstrated that the B biotype had the potential to displace the ZHJ2 biotype under laboratory caged conditions and revealed that asymmetric mating interactions between the two biotypes were the major behavioural mechanism underlying the displacement.(6) Behaviroual mechanisms underlying the displacement of indigenous biotypes ZHJ1 and AN by the B biotypeDetailed analysis of mating behaviour revealed asymmetric mating interactions between biotypes B and ZHJ1,or B and AN.The B biotype had higher sexual activity than the two indigenous biotypes in that B females were more receptive to males,and B males more frequently and efficiently courted female of the B biotype or another biotype.Besides,B males interfered more intensely with courtships initiated by rival males of another biotype than did indigenous biotypes.The B males interfered more successfully with courtships initiated by rival males of another biotype than by males of the same biotype,while indigenous males interfered more successfully with courtships initiated by males of the same biotype than by rival males of the B biotype. B males from both China and Australia could guard females post copulation,and more effectively inhibited courtships from indigenous males than from B males during guarding.However,indigenous males separated from females post copulation so that another male had access to court the females.All these behavioural differences between the biotypes had the consequences that copulation events between B males and females increased in the presence of indigenous males,while copulation events between the indigenous males and females decreased in the presence of B males.Also, in the presence of rival males of another biotype,female ratio in the offspring of B increased while female ratio in the offspring of the indigenous biotypes decreased. Copulation duration within each of the three biotypes was not influenced by the presence of another male,thus,we can conclude that as the consequence of asymmetric mating interactions between biotypes B and ZHJ1 or between B and AN, asymmetric change of copulation events resulted in the increase of female offspring of B biotype and decrease of female production of biotypes ZHJ1 and AN.These observations revealed the behavioural mechanisms underlying the widespread invasion and displacement of indigenous biotypes ZHJ1 and AN by the B biotype.Major new findings of this study:(1) We developed a cost-effective,efficient,and reliable video recording system for observing and recording the mating behaviour of whitefly on live plants.With this novel system,a large number of accurate and continuous recordings of courting and mating behaviour of this insect can be made on live plants under more natural condition.(2) We demonstrated that both pre-mating partial reproductive isolation and post-mating complete reproductive isolation between biotypes B and ZHJ2 of B. tabaci.(3) We found that under laboratory caged conditions the B biotype had the capacity to displace the indigenous biotype ZHJ2 in a short period of time and that the asymmetric mating interactions between the two biotypes were the behavioural mechanism underlying the displacement.(4) We revealed that the asymmetric mating interactions between biotypes B and ZHJ1,or between biotypes B and AN were the behavioural mechanisms underlying the displacement of the indigenous biotypes ZHJ1 and AN by the B biotype in China and Australia.