The Virus Transmission Efficiency Of Four Thrips And The Relationship Between The Occurrences Of Thrips And Virus

Thrips have the characteristics of small size, wide hosts, fast-breeding and strong adaptations. Except for harming crops by directly feeding scars, they can also transmit different virus of Tospovirus indirectly, which causes serious harm of host pants. To be a tipical virus of Tospoviruses, Tomato spotted wilt virus (TSWV) is distributing widely and harmed seriously in domestic. And which one is the prepondant transmission vector and the relationship between outbreaks of TSWV and thrips haven’t considered deeply yet. Therefore choosing four major thrips (Frankliniella occidentalis, Franlliniella intonsa, Thrips palmi, Thrips tabaci) that familiar and important to vegetables and horticultural plants, and Tomato spotted wilt virus as objectives, we have studied the acquiring and transmitting efficiency by these four thrips, and the relationships between the occurence of optimum vectors and TSWV, following are the results:1 Four thrips transmitted TSWV:Through hatching first-instar nymphs feeded on TSWV-infected stramonium leaves with a high acquisition efficiency, four thrips transmitted TSWV has found out:(Ⅰ) F.occidentalis adults have the highest acquiring and transmitting rates that finally up to 29.8%, which makes it become the best medium of TSWV that consistent with foreign researches. Meanwhile, F.intonsa takes the second place and T.palmi has a much lower efficiency only with 7.5%. (Ⅱ) Adults of T.tabaci can’t transmit TSWV successfully. (Ⅲ) Having a high virus acquiring rates doesn’t mean it can transmit highly at the same time. For example, F.intonsa and T.palmi both have the same acquiring rates at second-instar nymphs, but the final transmitting efficiency are far more than twice, which indicates TSWV particles needed to reach vectors’ salivary gland and accumulated to a certain threshold value.2 Researches about the optimum development of F.occidentalis by using Kerbs value analysis:Compared with pepper leaves, TSWV-infected and healthy stramonium leaves are both suiting for its growth and development. At the same time, the overall development trends of F.occidentalis (from first-instar nymphs to adults oviposition) are very consistant with contrasted healthy broad beans. Moreover, the total K-values’ tendency demonstrates that healthy mandala leaves being the best one for K-value analysis. However, the effect of both treated pepper leaves are relatively poor. In a word, all these illustrate that stramoniums are still very appropriate to be host plants for F.occidentalis and TSWV virus.3 The relationship study between numbers of F.occidentalis and TSWVdisease popularity in two mediated methods:(Ⅰ) Compared with TSWV-infected stramonium directly mediated, releasing TSWV-acquired F.occidentalis has a higher spreading transmission efficiency. (Ⅱ) The more numbers of F.occidentalis, the more mean numbers of virus acquiring plants and feeding scars in surrounding healthy stramonium, which indicates vectors’ numbers can exactly influence TSWV virus outburst and epidemiology. (Ⅲ) The plant TSWV infection rates of transmission by TSWV infectious vector F. occidentalis mediated (2%-10%) were evidently higher than that of transmission by infectious host plant mediated (0) after two weeks post treatment. It was not detected TSWV particles on host plant until three weeks, and the plant TSWV infection rates were less than 10% that transmitted by infectious host plant mediated. After six weeks, the plant TSWV infection rate reached 83.3% as transmission by TSWV infectious vector F. occidentalis mediated, and it was only 40% as transmission by infectious host plant mediated. (Ⅳ) Correlation exists between the mean numbers of virus acquiring plants and feeding scars in successive six weeks, it’s the premise for successfully acquiring virus to have feeding scars. Nevertheless, the final numbers of F.occidentalis haven’t shown the relevance, just as the vectors’ numbers don’t mean the high acquiring rates. In the end, the TSWV vector F. occidentalis obviously accelerates the speed of TSWV infection, and makes it more serious, which is important for making strategies of TSWV prevention and control.