Development of a bioassay system for monitoring susceptibility in Thrips tabaci

A system is described for collecting adult and larva of Thrips tabaci from onion foliage into insecticide-treated vials to evaluate susceptibility to insecticides. The thrips insecticide bioassay system (TIBS) allows one to treat vials and store them for 3 weeks before thrips are collected. Depending on the population density in the field, collection of the insects for the test required from 3-6 h for one person. Assays are read after 24h. This system was used in 1997 and 1998 in commercial onion fields in Honduras and Nicaragua, and TIBS was sensitive enough to detect differences to the insecticides tested, to thrips life stages and to different generations within an onion-growing season. Data collected suggest that there were not serious problems with thrips insecticide resistance, with the possible exception of cypermethrin in Nicaragua which had a resistance ratio (RR) value of 26.9 for adult thrips. The largest RR values were observed at the end of the growing season, and this may be caused by the season-long selection by insecticide sprays. The mortality of adults and larvae followed the same general pattern, but the ratio between larvae and adults differed for each chemical group.     

Analysis of Iris yellow spot virus replication in vector and non‐vector thrips species

Iris yellow spot virus (IYSV, genus Tospovirus) is a viral disease of bulb and seed onion crops and is transmitted by Thrips tabaci. Foliage damage of up to 75% has been reported in Kenya and Uganda. In this study, the rate of IYSV replication in the larva, pupa and adult stages of T. tabaci and other non‐vector thrips species and colour forms such as Frankliniella occidentalis, F. schultzei (dark) and F. schultzei (pale) was evaluated by monitoring relative levels of nucleocapsid (N) and non‐structural (NSs) proteins using N‐ and NSs‐specific antibodies. The effect of IYSV replication on mortality of thrips was also determined. N protein levels increased in all three stages of IYSV‐fed T. tabaci, indicating replication of IYSV. In IYSV‐fed non‐vector thrips, the increase of N protein levels in the larval stage was lower than IYSV‐fed T. tabaci but higher than their healthy counterparts. The N protein levels did not increase at pupal and adult stages. NSs protein was not detected in first instar of either vector or non‐vector thrips species. After a 4 h post‐acquisition period, a significant increase in NSs proteins was only observed in IYSV‐fed T. tabaci, clearly differentiating vectors and non‐vectors of IYSV. IYSV replication did not influence the survival of the vector thrips species, T. tabaci populations or the non‐vector thrips species. This study indicates the effectiveness of monitoring non‐structural proteins such as NSs, compared to nucleocapsid proteins, for differentiating vectors and non‐vectors of IYSV.     

鸢尾黄斑病毒几种PCR检测方法的建立和比较研究

 以带有鸢尾黄斑病毒的烟草叶片为材料,研究建立了IYSV的普通RT PCR、免疫捕获RT PCR和SYBR Green Ⅰ实时荧光RT PCR方法,并比较了几种检测方法的灵敏度。结果表明,DAS ELISA检测灵敏度较低,为1 mg带毒叶片。而各种PCR方法的灵敏度均高于DAS ELISA 100倍以上,其中SYBR Green Ⅰ实时荧光RT PCR检测灵敏度最高,可从0.4 μg的带毒叶片中检出IYSV,而RT PCR的灵敏度为40 μg带毒叶片,IC RT PCR的检测灵敏度是RT PCR的4倍。鉴于DAS ELISA灵敏度较低,建议在用ELISA初筛时,如样品OD405值与阴性对照OD405值之比在2.0左右时需要再用分子方法加以确证,以防漏检。     

A simple test for evaluation of transmission efficiency of barley yellow dwarf virus by aphids

Barley yellow dwarf virus (BYDV) transmission test systems involve the use of clip-cages or of whole plants in cages, which are both labor-intensive methods and require large controlled environment units. Employing detached leaves for assessment of the inoculation efficiency of aphids proved reliable for assessing transmission of a BYDV PAV-like isolate byRhopalosiphum padi. One use of the system could be for the rapid determination of the infectivity of field-collected aphids, an essential part of any epidemiological study of BYDV. http://www.phytoparasitica.org posting Aug. 14, 2002.     

Arabidopsis thaliana,an experimental host for tomato yellow leaf curl disease‐associated begomoviruses by agroinoculation and whitefly transmission

Tomato yellow leaf curl disease is one of the most devastating viral diseases affecting tomato crops worldwide. This disease is caused by several begomoviruses (genus Begomovirus, family Geminiviridae), such as Tomato yellow leaf curl virus (TYLCV), that are transmitted in nature by the whitefly vector Bemisia tabaci. An efficient control of this vector‐transmitted disease requires a thorough knowledge of the plant–virus–vector triple interaction. The possibility of using Arabidopsis thaliana as an experimental host would provide the opportunity to use a wide variety of genetic resources and tools to understand interactions that are not feasible in agronomically important hosts. In this study, it is demonstrated that isolates of two strains (Israel, IL and Mild, Mld) of TYLCV can replicate and systemically infect A. thaliana ecotype Columbia plants either by Agrobacterium tumefaciens‐mediated inoculation or through the natural vector Bemisia tabaci. The virus can also be acquired from A. thaliana‐infected plants by B. tabaci and transmitted to either A. thaliana or tomato plants. Therefore, A. thaliana is a suitable host for TYLCV–insect vector–plant host interaction studies. Interestingly, an isolate of the Spain (ES) strain of a related begomovirus, Tomato yellow leaf curl Sardinia virus (TYLCSV‐ES), is unable to infect this ecotype of A. thaliana efficiently. Using infectious chimeric viral clones between TYLCV‐Mld and TYLCSV‐ES, candidate viral factors involved in an efficient infection of A. thaliana were identified.