Feeding Behavioral Mechanisms Of Competitive Displacement Between Bemisia Tabaci Biotypes B And Q

The whitefly Bemisia tabaci (Gennadius)(Hemiptera: Aleyrodidae) is a complex speciescomposed of at least24morphologically indistinguishable biotypes. Among them, biotypes B and Q areregarded as the two most invasive and destructive whiteflies. In China, B biotype was first detected inthe mid-1990s. Since then, B has gradually replaced the indigenous species, and has been the majorwhitefly pest till2007. The situation started to change in2003when Q arrived in Yunnan Province,China. In the following years, biotype Q has rapidly displaced B in most part of China and has becomethe most dominant whitefly. In recent years, B. tabaci causes excessive crop losses through directfeeding and transmission of plant viruses. For example, Tomato yellow leaf curl virus (TYLCV),transmitted by B. tabaci in a circulative manner, caused disease epidemics in many regions of China. Inthis study, we used the electrical penetration graph (EPG) toolkit to look at elements from both theinsect (feeding behavior) and plant (host suitability) perspective to better understand the factorsinvolved in the competitive displacement of B. tabaci biotype B by Q. The main findings are listed asfollows.(1) Pair-wise comparisons of B. tabaci biotypes B and Q feeding on each of the five host plantsindicates that Q feeds better on tomato, cotton, and poinsettia, while B thrives on cabbage and cucumber.Our current results suggest that tomato, cotton and poinsettia are more suited for Q, while cabbage andcucumber are more suited for B. combined results from both insect and host plants suggest that hostsuitability and feeding behaviors displayed by adult whiteflies can affect their interaction and maycontribute to the rapid competitive displacement observed in China over the past6years.(2) The indirect (plant infection) and direct (whitefly infection) effects of TYLCV on the feedingbehaviors of B. tabaci biotypes B and Q were evaluated using EPG technique. When non-viruliferouswhiteflies fed on healthy and TYLCV-infected plants, respectively, B. tabaci Q engaged in more phloemsalivation and phloem sap ingestion than B. Plant infection by virus significantly affected10of24feeding behavior parameters. When non-viruliferous and viruliferous whiteflies infested healthy plants,B. tabaci Q fed more readily than B on tomatoes, regardless of the infection status of whitefly. Whiteflyinfection significantly affected9of24feeding parameters. Viruliferous whiteflies engaged insignificantly more phloem salivation, which associated with inoculation of TYLCV. These combinedresults support the hypothesis that B. tabaci Q is a more efficient vector than B, and that whiteflyinfection by the virus directly modifies the vector's feeding behavior in a manner which enhances viraltransmission.(3) Pair-wise comparisons of the feeding behaviors between B. tabaci biotypes B and Q onthiamethoxam treated and untreated TYLCV-infected tomatoes were carried out. The results showedthat biotype B probed more rapidly, while biotype Q fed more continuously and secreted more saliva on thiamethoxam treated tomatoes than on control ones. This indicated that thiamethoxam brought aboutgreater modification on the feeding behaviors for biotype Q than B, and biotype Q has more suitabilityto thiamethoxam treatment. The whitefly salivation is closely associated with TYLCV transmission.Thus the thiamethoxam treatment improved the TYLCV transmission in this study.(4) To evaluate the effects of endosymbiont, Hamiltonella, on feeding behaviors of B. tabaci, twoB. tabaci biotype Q colonies with the same genetic background, Hamiltonella-infeced (H+) anduninfected (H-), were established by antibiotic treatments and introgression. Comparisons of the feedingbehaviors on cucumber between the two colonies revealed that the Hamiltonella-infeced biotype Q(H+Q) reach the phloem phase more rapidly and easily than Hamiltonella-uninfeced biotype Q (H-Q).Obviously, the infection of Hamiltonella improved the fitness of whitefly. Meanwhile, the H+Q havehigher salivation frequency than H-Q, which indicated that the Hamiltonella is likely to improve theTYLCV transmission.(5) Feeding behavioral characters of long-term host isolated B. tabaci were examined. Three hostpopulations of B. tabaci biotype B with the same genetic background were established through rearingthe whiteflies segregated on cabbage, tomato, and cucumber for6years (hereafter referred to asCa-population, To-population, and Cu-population, respectively). Feeding behavior comparisons amongthe three host populations were carried out on each of the cabbage, tomato and cucumber plant,respectively. The results showed that Ca-population reached to the phloem phase more readily, secretemore saliva, and feed better than the other two host populations on any of the3host plants. Evidently,the feeding behaviors of B biotype were domesticated by adaptation for a long time on a specific hostplant, and the domestication degree varied with the host plants species.(6) Understanding the feeding behavior differences of the host specific B. tabaci biotype Bpopulations, the genetic differentiations of the3B biotype populations above and1additional Q biotypepopulation were further studied through AFLP and ISSR markers. The results indicated that thelong-term isolation of host plants induced a significant genetic differentiation for B biotype. However,the genetic distances among the three B biotype host populations were all lower than that between Band Q biotypes.In conclusion, B. tabaci biotype Q exhibited stronger host suitability, higher virus transmissionefficiency, and more adaption to the pesticide than B biotype. These factors may contribute to thecompetitive displacement of biotype B by Q.